A Short

History

and

Concepts

of

Color

Photography

1950s Photograph by Dennis Hallinan © FPG International

Annette RoulierImaging and Media Lab, 2008

entstanden im Rahmen von

nicephor[e](Programm des Swiss Virtual Campus)

e-learning course in scientific and forensic photography

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Contents

colors appliedby hand

direct colorphotography

indirect colorphotography

Lippmann processMicro-dispersion

AutochromeDufaycolorAgfacolor

Kodacolor

KodachromeAgfacolor NeuKodacolor

Silver dye-bleach Polaroid

color photography

additive processes subtractive processes

screen plateprocesses

lenticularprocesses

CarbroVivexPinatypyDuxochromeDye-TransferDye-Toning

assemblyprocesses

multilayerprocesses

chromogenicprocesses

chromolyticprocess

diffusionprocess

Tree structure of color photography

chromogenic processes: Composition of the colors.chromolytic processes: Destruction of the colors.

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Indirect three-color photography

1. Sensitizing

2. Color cameras

3. Additive color processes

3.1. The trichromatic theory of perception3.2. Screen-plate processes

3.2.1. The Autochrome plates3.2.2. The Dufaycolor process3.2.3. Agfacolor and Agfacolor Ultra

3.3. Lenticular processes4. Subtractive color processes

4.1. Photomechanical process (carbon process)4.2. Assembly processes (tri-pack)

4.2.1. The carbro (carbon-bromide) process4.2.2. The Vivex process4.2.3. The Pinatypy4.2.4. The Duxochrome4.2.5. The Dye-Transfer4.2.6. The Dye-Toning4.2.7. The separable tri-pack

4.3. Multi-layer processes (integral tri-pack)4.3.1. Kodachrome(reversalfilm)4.3.2. AgfacolorNeu(reversalfilm)4.3.3. Kodacolor (negative/positive material) and Ektachrome (slide)4.3.4. Further developments

4.4. Diffusion process4.4.1. The Polaroid process

4.5. Photofinishing4.5.1. Printing from color transparencies4.5.1.1. The silver dye-bleach (SDB) process4.5.2 Printing from color negatives4.5.3. Automatic methods of color printing

5. Coating techniques and drying

6. The introduction of digital cameras

Early color photography

1. Colors applied by hand

1.1. Laterna magica1.2. Hand-tinted photographs

2. Direct color photography

2.1. The Lippmann process2.2. The micro-dispersion process

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‘Color photography covers so many areas of human endeavour that its history is particularly fascinating. A purely physical approach was adopted by Lippmann, who attempted to reproduce the same spectral composition. A physiological approach was adopted by Maxwell, who attempted only to produce color matches to the eye. Subsequent attempts to make Maxwell’s method more convenient led to a wonderful variety of additive systems, some of which are the basis of modern color television. But color photography today is almost entirely carried out by means of the subtractive method in the form of the integral tripack, which is a marvel of sophisticated chemistry and engineering. For the successful application of inventions, timing is the essence. So many modern systems were foreseen by Du Hauron and Fischer decades before the necessary technology was available, and there is a wonderful irony in the fact that two professional musicians, Mannes and Godowsky, who were the first to produce a commercially successful tripack. The early days were dominated by motion picture systems, but the reflection print is now supreme. However, it was Evans, who came from the motion picture industry, who solved the difficult problem of printing from negatives by the ‘integrating to grey’ method’...

Robert W. G. Hunt

Timeline of concepts of color photography

1890

1900

1910

1920

1930

1940

1950

1960

1970

1980

1990

2000

direct color photography

screen plate processes

lenticular processes

assembly processes

chromogenic/chromolytic processes

diffusion processes

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Early color photography

1. Colors applied by hand

1.1. Laterna magica

In 1664, Athanasius Kircher presumably invented the Laterna Magica being inspired by Leonardo da Vinci’s drawings. The Laterna Magica worked like a slide projector with a candle or petroleum lamp and hand painted pictures on glass slides. Thus slide projection existed even before black and white photography was invented. The Laterna Magica was used until the twentieth century.

1.2. Hand-tinted photographs

Sincethefirstphotographicprocesshasbeenintroducedin1839,thesenseofwonder of those who saw the ‘light drawings’ dwindled because the colors of naturewerenotrecorded.Inanattempttocorrectthisdeficiency,itsoonbecamepractice to add color to the monochrome photographs while experimenters were busy seeking a way to record colors directly. Most photographers applied colors by imitating paintings rather than by simulating natural colors.

Talbot’s process used sensitized paper sheets for the positive prints that could easily be colored with water-colors or transparent oil paints.

Figure 1Laterna Magica (~1875) with a round glass panel that contains pictures of the novel of Robinson Crusoe.

Figure 3Hand-colored daguerreotype self-portrait by William Constable (1783-1861).

In 1842, Richard Beard patented methods of coloring Daguerreotypes and many others imitated him. Coloring a Daguerreotype image was difficultbecause the tiny silver particles were easily brushed from the polished non-absorbent metal plate. Beard suggested that: ‘The dry colors are stippled with a camel-hair pencil on to the different parts of the picture, using the colors required for each part. The colors are successively set by breathing over them.’

Figure 2Advertisement for a coloring service for photographers from 1861.

Figure 4Tinted photographic postcard, ~1905.

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2. Direct color photography

Photochromy or Heliochromy

(wavelength-dependent interference of light)

In direct processes, color-dependent structures are generated within the light sensitive layers of the recording material. When viewed in white light, these structures reconstitute the color information of the original subject. No dyes or filtersareinvolved.

In 1810, Johann Thomas Seebeck realized the first reproduction of thespectrum of light. He exposed a plate covered with silver chloride to light, split by a prism. The blackened silver chloride took the color of the spectrum but the impression vanished quickly.

Manyothersrepeatedhisexperimentsbutnoneofthemwereabletofixthecolors.

In 1840, John F. W. Herschel reported that he had been able to reproduce red, green and blue colors on silver chloride paper, which had been exposed to the spectrum. By washing the paper the colors became stable enough to be examined by lamplight.

In 1848, Alexandre Edmond Becquerel used silvered plates of the type of Daguerreotypes to take pictures. He coated them electrochemically with silver chloridetoformaverythinandevenfilmofsilverchloride.Thisfilmrecordedcolors especially pure and shiny forming a pattern of stationary waves. Edmond Becquerel was the son of Antoine Becquerel who constructed batteries and the father of Henry Becquerel who discovered the radioactivity of uranium.

In 1850, Reverend Levi L. Hill announced a method to produce Daguerreo-types in natural color by the action of light, called Hillotype. As he published his process not until the year before his death, he was suspected to be cheating people by using an elaborate technique in hand coloring. The many toxic chemicals involved in his work, some of them later used for chemical warfare in World War I, contributed to his death in 1865.

In 1865, Alphonse Louis Poitevin, a friend of Edmond Becquerel, contact copied glass paintings or fabrics on paper. He applied a solution of potassium dichromate, copper sulphate and potassium chloride to the silver chloride paper.

In 1867, Abel Niépce de Saint Victor,sonof thefirstcousinofNicéphoreNiépce,displayedsomeofhisheliochromesattheWorldExhibitioninParis,although he had to keep them in subdued light and replace them frequently.

Many scientists tried to explain the early direct processes and they found out that the colors are generated by a chemical adaptation (bleaching) of the silver layers that is not light proof. All these early attempts found no practical application.

Figure 5Picture taken in 1859 with the method described by Becquerel. It has to be kept in the dark.

Figure 6Edmond Becquerel (1820-1891).

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2.1. The Lippmann process

In 1891, Gabriel Lippmann developed a method of reproducing colors, based on the interference phenomenon. He introduced it to the Paris Academy of Sciences publishing his invention without patenting it. Lippmann produced the firststablecolorpicturesusingadirectphotographicprocess.In1893hewasable to present to the Academy portraits taken by Auguste and Louis Lumière, in which the colors were produced with perfect ortho-chromatism. For his method he was awarded the Nobel Prize for physics in 1908.

The Lumière brothers fostered Lippmann’s method with enthusiasm before they invented the Autochrome process. They developed special emulsions and produced slides, which they projected with arc light.

Figure 9Section through an exposed and developed emulsion, showing the laminae.

Figure 8Still life 1891-1899.

Figure 7Gabriel Lippmann (1845-1921).

The principles of the process:Thecolorsare formedby interferencease.g. inanoilfilmonwateror inasoap bubble. The panchromatic (sensitive across the whole visible spectrum) emulsion contains extremely fine grains in order to record the interferencepatterns. It is coated on a highly reflective mercury back layer. Duringexposure,theincominglightinterfereswithitsreflectionandstandingwavesare generated with peak intervals according to the color (wavelength). After developmentandfixationtheblackenedsilvergrainsareatruereplicaofthestanding wave pattern. When viewed in white light at normal incidence, the standing waves and thus the colors are reproduced.

The technique was not very practicable for color photography since it was complicated, expensive and required long exposure times. The pictures could not be copied, inhibiting a commercial success. The Lippmann process resemblestoday’sreflectionholography.

2.2. The micro-dispersion process

In 1895, F. Lanchester patented the micro-dispersion process. The object was photographed through a grating consisting of parallel lines of about 300 lines per inch, alternately transparent and opaque. The grating was placed as close to the object as possible. There was a prism in front of the lens with its axis parallel to the bars of the grating, dispersing the light into minute spectra. A positive contact print from the processed negative was placed in exactly the same position as the negative when exposed. Projected back through the system it formed a reconstituted color image. As his method was very unpractical, Lanchester is more likely to be remembered for his motor cars than for his contribution to color photography.

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Indirect three-color photography

1. SensitizingColor photography principally calls for “sensitizers” in order to expand the light sensitivity of the silver halide emulsions to the total visible spectrum. Orthochromaticfilmsaresensitivetoblueandgreenlight,panchromaticfilmsare sensitive to the whole spectrum. However, panchromatic emulsions were available only after the early 1900s.

In 1873, Hermann Wilhelm Vogel discovered by chance that the pink dye “coralline could” be used to extend the sensitivity of silver halides into the green region of the spectrum. He used commercially prepared collodion plates tinted with pink dye to reduce halation and discovered that the plates showed a maximum of sensitivity to green light. Vogel interpreted this maximum as sensitivity to light absorbed by the dye (the dye adsorbs very strongly to the silver halide and makes it sensitive to longer wavelengths). Once his principle hadbeenconfirmed,thediscoveryofnewandmoreeffectivesensitizingdyeswas rapid.

Figure 10Hermann Wilhelm Vogel (1834-1898).

In 1884, Josef Maria Eder, who first questioned Vogel’s discovery, foundthat erythrosine gave excellent sensitivity in the green and yellow part of the spectrum.Thisledtothefirstcommercialorthochromaticplates.

In 1903, Adolf Miethe and Arthur Traube got a patent for the use of the dye ethyl-red that extended the sensitivity of silver halides into the orange-red region of the spectrum. The Perutz Company in Munich used the dye to producethefirstpanchromaticplates.

In 1906, Benno Homolka, a chemist at Farbwerke Worm Meister Lucius und Brüning discovered pinacyanol achieving adequate red sensitivity to produce thefirstaccuratelypanchromaticplate.

2. Color camerasBeforetheinventionofmultilayerfilms,earlymonolayercolorphotographymetthechallengetoconstructcameras,whichallowedtriplefilteredexposureinone shot.

It is necessary to differentiate between early suggestions for single exposure color cameras and proposals for Chromoscopes intended only for the additive viewing or projecting of color separation positives.

At the latter half of the nineteenth century stereoscopic photographs were very popular. They probably inspired du Hauron, Cros, Ives and many others to build viewing instruments, called Chromoscopes, to combine red, green/yellow and blue glass positives made from separation negatives without the need for either projection or printing. At that time it was not sure whether a yellow or greenfiltershouldbeusedtogetherwithanorange-redandablue-violetone.

In 1876, Louis Ducos du Hauron describes a camera, with which three negatives could be exposed simultaneously, realizing that a Chromoscope could easily be adapted to become a color camera.

Figure 11One of du Hauron’s suggestions for a chromoscope, called chromographoscope, invented in 1874. It could be used either as a camera or an additive viewer.

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In 1892, Frederick Eugene Ives devised a camera, with which he could make threeexposuresthroughcolorfiltersonasingleplate,dividingthebeamfroma single lens by a system of mirrors. In the following years he invented several other types of color cameras.

Ives also constructed viewing instruments called Kromskops to optically superimpose the three filtered positive imagesmade from color separationnegatives. There were Kromskops for projection and for direct viewing of monocular or stereo color images. Ives took color negatives, especially in Europe, selling sets of positives to owners of Kromskop viewers. At the turn of the century a Kromoskop cost in Germany 200.- marks and a set of slides cost 6.- marks.

Throughout his live Ives stated that he had no knowledge of Maxwell’s method of color reproduction and he tried to belittle the work of du Hauron and Cros. But in the end Ives was forced to admit: ‘It is true that this is not exactly the kind of color photography that the world has been looking for … because it does not produce fixed color images, which can be framed and hung upon the wall.’

The following inventions were led with the intention of reducing the time required to complete the three exposures.

In 1897, J. W. Benetto patented a camera, with which the three separation negatives were obtained at a single exposure, requiring only two plates (bi-pack and one) being exposed by a split light beam. One of the plates contained oneplateandonefilmwith theiremulsionsides incontact, theplatebeingnotsensitizedandthefilmsensitizedtothegreenspectra.Atthebackofthecamerawasaredfilterinfrontofapanchromaticplate.Exposuretimescouldbe shortened and because any movement of the subject was recorded equally on all three negatives, no color fringing has resulted. The camera could also be used for black and white photography.

Figure 12Camera invented by J. W. Benetto.

Figure 13 (left)‘Miethe three color camera’ built from 1899-1929 by Bermpohl.

In 1899, Adolf Miethe launched a camera, which allowed the making of exposures in succession by means of sliding a triple plate holder (repeating back), that worked with gravity, containing the necessary plates and color filters.

In 1906, J. S. Chenhall patents a camera with a clockwork-driven plateholder, the movements of the plates being synchronized with a lens-mounted shutter.

Atthebeginningoflastcenturyitwasnolongernecessarytousethreefiltersto get the chromatic selections because there were specially sensitized plates available. Despite the fact that time parallax must always result from making a sequence of exposures of a moving subject, many kinds of repeating backs were used until World War II.

In 1910, L. Geisler patented the manufacture and use of a thin membrane stretchedover a flatmetal framebecoming knownas pellicle. Its use as asemi-reflectivesurfaceavoidedalltheshortcomingsoftheglassreflectorsandafter 1930 pellicles were used in most of the color cameras.

Assoonasitbecameclearthatmulti-layercolorfilmslikeKodachromeandAgfacolor could be used in any kind of camera, the era of color cameras came to an end.

Figure 14 (below)In the mid -1930s the Reckmeier camera was intro-duced. It was the first single exposure color camera constructed from a metal body cast in one piece and using pellicle reflectors.

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Figure 16White light split by a prism.

Figure 17James Clerk Maxwell (1831-1879) at a meeting of the Royal Institution on May 17th 1861.

3. Additive color processesFor the additive process, the image is the result of separating white light into blue, green and red, then adding or mixing controlled portions of these colors toformthefinalimage.Theonlypracticalmanifestationsofphotographyusingadditive color were the various screen-filter processes. These processesrequired light transmitted through blue, green and red filters. The image isformed by selectively transmitting or blocking the light by a screen.

In 1611, Marco Antonio de Dominis synthesized all colors of light by mixing just three: red, green and violet.

In 1666, Isaac Newton discovered that sunlight can be split with a prism into itsconstituentcolorsandreunitedtowhitelightagain.Hedefinedsevenbasiccolors: violet, indigo, blue, green, yellow, orange and red.

Figure 15The colors are formed by mixing red, green and blue light.

3.1. The trichromatic theory of perception

In 1801, Thomas Young proposed to the Royal Society of London that our ability to perceive colors depends on three different types of nerve fibersin our eyes, sensitive to reddish, greenish and bluish light respectively and that the variety of sensations we call colors result from the stimulation of the nerves to different extents. His concept was later extended by James Clerk Maxwell and Hermann von Helmholtz. Young became famous with his double slit experiment about interference. He concluded that light is a wave motion whose wavelength determines the color.

In 1861, James Clerk Maxwell gave a lecture to the Royal Institution in London, which can be considered the start of color photography as we know it today. During that lecture he demonstrated the theory of three primary colors as follows:

‘Three photographs of a colored ribbon taken through the three colored solutions respectively, were introduced into the camera, giving images representing the red, the green and the blue parts separately, as they would be seen by each of Young’s three sets of nerves separately. When these were superposed, a colored image was seen, which, if red and green images had been as fully photographed as the blue, would have been a truly-colored image of the ribbons. By finding photographic materials more sensitive to the less refrangible rays, the representation of the colors of objects might be greatly improved.’

Maxwell took three black and white photograps on glass plates of a colored ribbon each through a color filter (blue, green and red). After developmentandfixationheusedlightofcorrespondingcolortosuperimposethesethreeimages with a projector on a screen; the colored ribbon was reproduced.

Figure 18Color print of the positive plates used by Maxwell for his demonstration to

the Royal Institution.

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Maxwell’s demonstration with today’s knowledge leaves a technical question: The wet-collodion plates he used were only sensitive to ultraviolet radiation, blue and very slightly to blue-green light (Hermann Vogel discovered the color sensitization of photographic emulsions only 12 years later). It was not until a hundred years later that Ralph M. Evans of Eastman Kodak revealed that theredfilterusedbyMaxwelltransmittedappreciableamountsofultravioletradiation. Looking at the reflection characteristics of some red fabrics, hefoundthattheyoftenreflectedultravioletraysaswellasredlight.Thustheredphotograph was effectively an ultraviolett photograph. Evans explained:

‘Maxwell’s ingenuity in devising a proof by the new technique of photography for an old theory of Young’s on the three-color nature of vision, …, led to the invention and demonstration of color photography some 20 years before it was possible.’

plate, the glass side of the screen-plate facing the lens of the camera. From the resulting negative a positive was produced by either contact printing or by reversal processing. The positive was then placed in contact with a ‘viewing’ screen-plate bearing exactly the same pattern of lines as the ‘taking’ screen-plate. The dyes for the ‘taking’ screen had to be diluted to provide wider transmission bands because the emulsion of that time required exposure times of at least one second in bright sunlight when used behind the screen-plate. Screen-plateprocessesrequiredpanchromaticemulsionsthatweredifficulttoobtain at the turn of last century.

Figure 19Triple lantern of the 1890s (Lancaster’s Triple) to project separation positives.

1 2 3 Figure 20Schematic illustration of the additive screen-plate process.1) Green light affects only the silver halides behind the green filters.2) Removal of the resulting silver deposits leaves residual silver halide behind the red and the blue filter.3) A second stage of development causes silver deposits behind those filters allowing only transmitting green light. (The scheme can be applied analog for red or blue light).3.2. Screen-plate processes

In 1892, James William McDonough patented a random patterned mosaic filter anticipating the very successfulAutochromeplate.Heuseda layer offinelygroundparticlesofred,greenandbluedyedshellac.

In 1894, John Joly following concepts of Louis Ducos du Hauron (see subtractive color processes) patented a method to achieve Maxwell’s result withafilter ‘all inone’.Hepatentedamachine toapplyparallelblue,greenand red lines onto a gelatin layer on glass plates with a density of 200 lines per inch. These plates were called screen-plates. The development of such an elaboraterulingmachineisthefirstofmanyexamplesofthedependenceofcolor photography on precision engineering.

The process:The ‘taking’ screen-plate was placed in contact with the emulsion of a glass

Figure 21Photomicrographs of a selection of color screen plates.

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Despite their commercial failure the efforts of Joly and McDonough encouraged many others to produce different forms of screen-plates, of which Autochrome and Dufaycolor were the most successful.

3.2.1. The Autochrome plates

In 1904, Auguste and Louis Lumière patented the idea of an additive screen-platefiltermosaiccontainingdyedgrainsofstarchandin1907theAutochromeplates were launched.

The Lumière brothers operated a factory producing black and white photographic glass plates called ‘Etiquette Bleue’, in Lyon (France) and they were the largest photographic manufacturers in Europe. Their company also producedthespecialfinegrainemulsionrequiredfortheplatesusedfortheLippmann interference process.

The Lumières knew du Hauron and his work well and when he was in his last years, they took care of him. Following du Hauron’s subtractive principle Louis Lumière produced a series of prints setting a standard that far exceeded any previous work.

Themosaicfilterwasprotectedbyavarnishandcoveredwiththeemulsion.Sensitizingdyesandfiltershadtobeusedtogetcolorsensitivitythroughoutthevisible spectrum. To obtain the positive after exposure, reversal processing was used: The negative black and white image was developed and the developed silver was bleached with dichromate, which converts silver to relatively soluble silver chromide, which can be washed out. Then the residual sensitive silver halideswereexposedtolightandthepositiveimagewasdevelopedandfixed.Nowthepicturecouldbeviewedthroughitsmosaicfilter.

Autochrome plates were very slow, 30 times slower than a typical black and white emulsion of those days, and a tripod was essential! Estimating exposures musthavebeenverydifficultbecausetherewerenoexposuremetersofthekind we know today and the exposure of any reversal transparency material is far more critical than the exposure of a negative.

The process:The starch grains had to be extremely small in order not to be visible at normal viewing distance and they should not vary much in size. Appropriate grains were selected by elutriation (separating the lighter from the heavier particles of a powder by washing). Three equal quantities of grains were dyed, blue green and red, mixed and evenly distributed over the plates. The dyes were remarkably stable, showing little change after almost a century. In practice some‘clumping’ofgrainsinevitablyoccurred.Thegrainswereflattenedunderpressuretospreadthemandanyremaininggapswerefilledwithcarbonblackpowder.

Figure 22Auguste (1862-1954) and Louis (1864-1948) in their laboratory at Lyon in 1892.

Figure 23Enlarged section of an early Autochrome screen-plate (~3’000 grains/mm2).

Figure 24Reproduction from an Autochrome, probably exposed by Louis Lumière himself.

Figure 25Autochrome plates didn’t transmit more than about 10% of the incident light. To make it easier to view the plates, many people used a diascope, with which light from a window or lamp would illuminate the transparency, the image of which could then be viewed via a mirror.T

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Nevertheless their extremely low speed and the relatively high risk of failure, the Autochrome plates remained popular from 1907 until the mid-1930s and likely some 20’000’000 plates were exposed during this period as the Autochrome process yielded the best color transparencies of that time.

Soonafter theFirstWorldWar(after1918), theuseof roll-films inhandheldcamerasrapidlyincreasedandtheLumièreshadtofindawaytoproducetheAutochromeprocessonafilmbase.In1932theylaunchedLumicolor,thefilmversionoftheAutochromeprocess.Lumicolorwasfasterthantheplatesbecausethegrainscouldbeflattenedandtherewasnomoreneedofgapfillingcarbon. At about the same time Eastman Kodak introduced Kodachrome, the firstmulti-layersubtractivecolorfilm.AlthoughtheLumièresintroducedanewversion in 1952, called Altipan, there remained no future for additive processes.

3.2.2. The Dufaycolor process

In 1908, Louis Dufaypatentedamethodtoproduceageometricfilterscreenforscreen-plates.Themethodwasusedinmodifiedformsandundervariousnames for over forty years, covering much the same period as the Autochrome process.DufaycalledhisfirstplatesDioptichromes.Saleslastedonlyafewyears, possibly because war made it impossible to continue.

Afterthewarherenewedhisprocess,thistimeonfilmbase,nodoubtwiththe rapidly expanding motion picture business in mind. In 1920 the company laSociétéVersicolorwas formed, offering not only films (calledVersicolor-Dufay), but also a negative/positive paper print process that was unsuccessful and soon abandoned. After several sales, Ilford Limited was by the end of 1935 incontrolofthecompanycalledDufayChromexLtd.Atthetime,thefilmwascalled Dufaycolor.The Dioptichrome process was very complicated. Because there were no gaps

tobefilledbetweenthefilterelements,theDioptichromeswerefasterandmoretransparent than the Autochromes. Another advantage of the Dioptichrome was the possibility to use separate taking and viewing screens, which made duplication easy. But the resolution of an Autochrome was far superior to a Dioptichrome.

The Dufaycolor process (the build-up of the screen-plate is explained in the figurebelow):The dyes were protected by a thin layer of varnish and then coated with an emulsion,appliedbyIlford.Exposureandviewingweredonethroughthefilmbase. Even though Ilford used their fastest panchromatic emulsion, the speed ofthefilmwasonly~ISO8.Thereasonforthelowsensitivity,commontoalladditiveprocesses,wasthatmorethan75%ofthelightreachingthefilmwasabsorbedbythefilters,demandingpowerfullightsourcesfortheprojection.

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Figure 271) A thin layer of collodion was applied to the film base and then dyed blue, before being imprinted with a pattern of parallel greasy ink lines.2) The unprotected areas of the collodion were bleached.3) The bleached areas were dyed green.4) The greasy ink lines were removed and another set printed at right angles to the original pattern.5) The areas between the protected lines were bleached.6) The bleached areas were dyed red.Figure 26

Louis Dufay (1874-1936). Figure 28In the 1930s, many amateur photo-graphers were able to take color snapshots for the first time using hand-held roll film cameras and the Dufaycolor process.

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3.2.3. Agfacolor and Agfacolor Ultra

In 1932, I. G. Farbenindustrie (Agfa) introduced a mosaic screen additive processthatwasinsomewayssimilartoAutochrome.TheAgfamosaicfilterlayer was composed of three solutions of dyes in colloidal suspension instead of dyed starch grains. Because the dyed droplets dried in close contact to each othertherewasnoneedforcarbonblacktofillthegapsbetweenthemaswasnecessary with Autochrome plates. Thus Agfacolor and Agfacolor Ultra were faster than Autochromes and have been sold between 1934 and 1938.

Figure 30Agfacolor-Ultra, Hungary 1937.

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Figure 31Schematic illustration of an additive lenticular process. After exposure, the panchromatic emulsion layer is processed by reversal. Without being projected through the corresponding filter, the lenticular film looks like a black and white film.

Figure 29Wrapping of the Agfacolor-Ultra film pointing out the different film type to avoid confusion because the Agfacolor lenticular film was sold at the same time.

Despite all limitations the screen-plate systems were less complex to use than the only alternative substractive systems involving making separation negatives and then producing the positive by using complicated assembly-processes.

In the mid 1930s Kodachrome and Agfacolor (multi-layer processes) replaced all screen plate processes. After World War II (1945) the progress in the development of multi-layer materials was rapid and substantial, so both thetechnicalandthefinancialinterestsinadditiveprocessesquicklydeclined.Today the only use of the additive process is in television and digital imaging. The last additive product was Polachrome CS by Polaroid, an “instant” 35mm

color transparency.3.3. Lenticular processes

In 1896, Raphael Eduard Julius Liesegang outlined the use of a banded tricolorfilteronthecameralenstogetherwithacross-linescreentoactwithamultitude of pinhole lenses.

In 1909, Rodolphe Berthon was the first to patent the method of usinglenticulations in a system of additive color photography. He used a banded tricolor filter inside the lens of the camera together with tiny lenticulationsembossedononesideofthefilmformingcountlesstinyimagesofthatfilteron the sensitive surface. In his patent he showed two forms of lenticulation patterns: a regular pattern of tiny spherical lenses and one of parallel cylindrical lenses. Berthon thought of producing separate embossed sheets that could be laminated to glass because at that time most photographers still used glass plates. After the War he joined forces with Albert Keller-Dorian who patented

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amethodofproducingcontinuouslengthsofembossedfilms(22lenses/mm2).In 1928, Eastman Kodak launched the Kodacolor system after acquiring the rights from the Keller-Dorian Berthon Company. The photographer had tobuyaspecialcamera,acorrectlybandedfilterforeachbatchoffilmandacorrespondingprojectororaconversionkitbeforehecouldusethe16mmfilm.The system was withdrawn in 1937 after limited success.

InEuropeAgfaproducedthelenticularfilmsforbothamateurmoviesandstillphotographstakenwiththeLeicacamera.Thefilmdifferedonlyinresolutionfrom the American equivalent (lenticulations in 0.028mm width against

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Figure 32Agfa lenticular movie film.Top: Lenticular film. Bottom: Lenticular film as viewed through the corresponding filter.

Figure 33Leica, with a stripe color filter on the objective, to take pictures on lenticular films.

0.043mm).In 1936, Perutz Photowerke München showed in Berlin the film “Das Schönheitsfleckchen”, which was produced after the Berthon method. Because the medias showed such a great interest in the product of their competitor, Agfa forced the launching of Agfacolor Neu and the development of the Agfacolor negative/positive print process (see page 24).

Between the 1920s and the 1950s very large sums of money were invested into the lenticular system but with no commercial success. Apart from poor light efficiencyandproblemsmakingcopies, the lenticularprocessalsosufferedfrom degradation of colors resulting from light-scatter. In the early 1950s, soon after the introduction of the Eastmancolor negative/positive process, the

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lenticular process was abandoned.

4. Subtractive color processesFor the subtractive processes, the image is the result of subtracting blue, green and red from white light using superposed layers of yellow (minus blue), magenta (minus green) and cyan (minus red) dye. For all the subtractive

sensitized with bichromate of potash, dried and then exposed. The gelatin layer hardened according to the amount of light it received. The tissue was pressed in contact with a sheet of paper, and immersed in hot water. The unhardened gelatin dissolved, leaving a monochrome relief, the density depending on the thickness of the colored gelatin (there was no silver involved in this process).

Louis Ducos du Hauron and Charles Cross independently described the subtractive process finding technical solutions for Maxwell’s trichromatictheory of perception.

In 1876, Louis Ducos du Hauron got a patent involving his many ideas on color photography. It was already in 1868 that he got a patent entitled ‘Les couleurs en photographie – solution du problème’ but the importance of his

processes, these dye layers are formed in, or deposited on, the emulsion of photographicpaperorfilm.In 1722, Jacques Christophe le Blon, an engraver and painter, devised a method for the subtractive color synthesis and proved later with his practical work that any color as well as black, in paintings or copperplate engravings, can be composed by superimposing red, yellow and blue pigments/inks. His problem was that the proportion of each color could not yet be determined. Le Blon’s theory survived in chromolithography and is the basis of modern color printing.

In 1796, Aloys Senefeldermadethefirstlithographyprints,thebaseforoffsetprinting. Before it was necessary to make a relief from the original (copper plate engraving). Senefelder copied by hand the inverted original with greasy ink or chalk on a plane stone surface (lithos=stone, graphein=write). After watering the surface, the greasy printing ink adhered only to the marked parts but not to the wet surface, owing to the fact that grease and water do not mix. Many prints could then be obtained from the same original.

In 1837, Godefroy Engelmann patented the Chromolithography (lithography with four colors). This method involved reprinting the picture (painted by hand) for each color or combination of colors. Great care had to be taken to align the paper carefully to avoid fuzzy contours. Chromolithography was common for high quality color prints until the thirties of the 20th century.

4.1. Photomechanical process (carbon process)

In 1864, Joseph Wilson Swan patented a ready-made carbon tissue. The tissue was made of a thin sheet of gelatin colored with powdered carbon. It was

Figure 34Overlapping or mixing of dye.

Figure 35Autochrome plate of Louis Ducos du Hauron (1837-1920).

ideas was not recognized as he could offer no proof. His two patents contained the basis of all subsequent subtractive color processes.Du Hauron also patented several devices such as a couple of Chromoscopes and a device for stereoscopic photography called Anaglyph. In addition he patenteda‘mosaic’filteradditivescreenplatepermittingonlyoneexposure,an idea that led to the basics of screen plate processes. Du Hauron never managed to gain money from his inventions. He was made a Chevalier of the French Legion of Honor in 1912, receiving belated recognition.

DuHauronwasfirsttorecognizeanddescribethesubtractivemethodof

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Figure 36The rooster, 1879 by Louis Ducos du Hauronheliochromie au carbon.

color photography abandoning the idea of recording color by direct processes. He can be considered as the “father of color photography”.The process:According to his 1876 patent, du Hauron simultaneously took three pictures with three objectives that were equipped with a violet, a green and an orange filter. Then he contact printed the negatives on tissues, each colored withyellow, red and blue pigment and sensitized with a solution of potassium bichromate (trichrome carbon process). The sheets were immersed in water where the soft (non exposed) gelatin was washed out. Then, the remaining gelatin was transferred by contact onto glass plates. Later, the gelatin layers of the resulting monochrome positives were superimposed onto a paper, creating a full-color photograph. The problem of superimposing the pictures madeitdifficulttocommercializetheprocess.Becausethecolorswereonlycomposed of pigments, they were very stable.

The wet plate emulsions had to be sensitized to green and red light, supplying a linear identity of the three proofs. To solve this problem du Hauron could refer to the discoveries of Vogel and Becquerel but it is likely thatexposuresthroughtheredfilterweresolongthatitwashardlypossible

to record live subjects. The exposure time took several seconds in sunlight asking for a camera that created three pictures simultaneously.In 1869, Charles Crospublishedapaperwiththetitle‘Solutiongénéraleduproblème de la photographie des couleurs’. When he heard of du Hauron’s work, he revealed his work being deposited at the French Academy of Sciences in 1867. Before neither du Hauron nor Cros knew about each other’s work and it is remarkable that they were ready to share reputation without jealousy. Cros

Figure 37Charles Cros (1842-1888).

was also a poet and artist. He didn’t implement his ideas in practice being content with the honor of discovery.The theory:The three color-separated parts of a picture (red, yellow and blue) should be exposed on black and white plates, one after another or simultaneously. Cros also mentioned the possibility to illuminate the subject with red, green and blue light.

Makingseparationnegativesinthe1870swasextremelydifficult,neverthelessDucos du Hauron and Cros discovered the imaginary base for many future techniques.

In 1882, Georg Meisenbachproducedthefirstautotype,aphotomechanicalreproduction method. He managed to transcript the tone gradation of photography to dots of different sizes. Meisenbach placed a screen between objective and emulsion. It consisted of fine parallel diagonal lines on glassplates producing a cross-screen. Then the incremental negative was copied on a plate covered with emulsion. After the development the space between the dots was etched producing a screened relief.

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In 1901, Albert Münch improved Meisenbach’s method by rotating the screen 30°toavoidtheMoiréeffect.4.2. Assembly processes (tripack)

Until 1935 the subtractive assembly process provided the only way of making colorprints.Itwasadifficultandlengthyactionthatveryfewpeoplemastered.Nevertheless there was a latent desire for color photographs on paper. Oneattempt tosimplify theassemblingwas theuseofstrippingfilms.Afterexposing the films, relief images could bedeveloped inwarmwater beforebeing transferred directly and in sequence onto paper.

At the beginning of the twentieth century exposure in the studio took still about ten seconds despite the use of arc lighting, sensitized plates and

the carbro process. The Autotype Company put his process on the market and continued to promote it until after World War II.The monochrome carbro process:A bromide print was put in contact with a sensitized, colored gelatin tissue while wet. The gelatin hardened according to the amount of silver due to chemical reaction between the sensitizer and the silver of the bromide print. The bromide print and the tissue were separated, the carbon tissue was transferred on the finalsupportanddevelopmentproceededasinthecarbonprocess(seepage15).

The trichrome carbro process:Silver bromide paper enlargements were made from the three separation negatives. The process worked in the same way as the carbro process except that pigment tissues of the three colors cyan, magenta and yellow were used. After being squeezeed into contact with the bromide print the tissues were put on temporary supports, developed and assembled on another temporary supportbeforebeingtransferredtothefinalsupport.Sincethefinalprintmusthavethecyanimageontop,adirecttransfertothefinalsupportwouldhave

Figure 38Three color carbon print from sepa-ration negatives (1907).

repeating backs. Therefore not many color prints were free from color fringing, due to movement of the subject, asking for a single exposure camera.4.2.1. The carbro (carbon-bromide) process

In 1905, Thomas Manly patented the Ozobrome process. A silver image was treated with a mixture of ferricyanide and dichromate, and then squeegeed to a pigment tissue. The products of the action on the silver were transferred to the tissue, rendering this insoluble, and the carbon print could be developed in warm water.

In 1919, H. F. Farmer improved the Ozobrome process becoming known as

Figure 39Trichrome carbro print of ‘Camel cigarettes, Girl in pool’ by Nickolas Muray (1936).

meanttofitthemagentaontotherelativelypaleyellowimage,whichwasverydifficult.4.2.2. The Vivex process

In 1928, Colour Photographs Ltd. was formed. Just before World War II ninety percent of the color prints made in the UK were produced by the Vivex process, a derivative of the trichrome carbro process. One of the most important features of this process was the use of waxed cellophane as a

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temporary support for the pigment relief image. This allowed to correct small mis-matchings of the component images, resulting from subject movement, by manually stretching or squeezing the cellophane.The company insisted on measurement and control requesting inclusion of a test chart on the photograph, permitting bromide prints based on density

measurements. The company was only in business for a decade, but they establishedthefirstprofessionalcolorprintingserviceandproducedsomeofthe best prints made by any assembly process.Du Hauron’s concept of a three color carbon printing process was in use almost during a century. At the end of this period, the only difference was that the pigment images were obtained via bromide sheets and waxed celluloid or Perspex sheets were used instead of glass. One of the most important features of the carbon and carbro processes has always been the good permanence of the images.

4.2.3. The Pinatypy

In 1905, Farbwerke Worm Meister Lucius und Brüning (now Farbwerk Hoechst AG) patented the Pinatype process, based on the different staining action of certain dyes for hard (won’t be dyed) and soft (will be dyed) gelatin. Three positives, called printing plates, were made from the separation negatives and developed in a tanning developer to harden the gelatin in proportion to the silver present. The positives were dyed yellow, red and blue and successively put in contact with a blank gelatin coated sheet of paper, which adsorbed the dye of the colored transfer sheets. The colors of these prints were less intense

than those of the carbon printings and the process was very time consuming. Although the process offered the possibility to obtain a number of prints from the same set of print plates, it was never as popular as the carbro process.4.2.4. The Duxochrome

In 1929, Johannes Herzog & Co. introduced the Duxochrome (Herzog = duke) process. The process was very successful in Germany and was used until the beginning of the sixties. Three different films, coated with silverhalide emulsion and colored with a non-diffusing cyan, magenta or yellow dye (lightfastazo-dyes),wereused.Thefilmswereexposedthroughtheirbaseto

Figure 40Vivex also launched a camera (Vivex ‘one-shot’) being con-sidered small at that time but still weighed 6 kilos. It allowed exposures of 1/50th seconds in bright sunlight.

Figure 41Duxochrome slide of an advertisement for Lucky Strike cigarettes (around 1935).

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the appropriate separation negatives then the silver halides were developed and a colored relief image was obtained after treatment in hot water (the gelatin hardened according to the amount of silver). The residual silver was removed and the three relief images were transferred and assembled onto the finalsupport.4.2.5. The Dye-Transfer

In 1945, Eastman Kodak launched a new process called Dye-Transfer. In 1935 Kodak had introduced a method of making color prints on paper called Wash-Off Relief process and ten years later when a new version of the process was introduced its name changed to Dye-Transfer. The new process could be completed in half an hour and extremely sharp prints could be made. In 1949 Kodak introduced thePan-Matrixfilm (panchromatic) forusewithEktacolornegatives, so that a set of three matrixes could be obtained by red, green and

a tanning developer. The un-tanned emulsion was washed away in hot water, leaving an image looking like an ordinary positive except that it was in relief. The three matrices were dyed in cyan, magenta or yellow dyes and brought inturnintocontactwiththefinalpaperabsorbingthedyeoutofthematrices.Thedefinitionoftherelativeexposureforthethreematrices,givingthecorrectcolor rendering in the print, was a problem common to all separate image color printing processes. To solve this problem, the separation negatives included a grey scale being on the matrix as a reference.

The advantage with respect to the carbro process was that one set of matrices could be used for up to 150 prints. The main disadvantage of this process was its inability to make adjustments between the three color images, if they were not well registered.

4.2.6. The Dye-Toning

From three separation negatives, positives were made. These silver images were converted into silver iodide or copper ferrocyanide (=bleached), which will serve as a mordant for basic dyes (mordant = substance adsorbing and holdingdyesespeciallystrong).Afterwardstheimagesweredyed,fixedandsuperimposed.

In 1922, Arthur Traube introduced a process called Uvachrome (uva = grape =Traube), a dye-toning process. TheUvachrome process used film-basedmaterials for the original positive silver images, and was intended for making transparencies that required much less projection light than any of the screen-plate processes of that time. The resolution of the dye toned subtractive image would have been superior to the additive processes but the process has not been used for color print making, although Traube did suggest that a stripping celluloid could be used.

Oneoftheprincipaldifficultiesofthedye-toningprocesswastofindasuitablysensitive material, on which to print the necessary positive silver images.

bluefilteredexposuresmadedirectlyfromthenegative.Althoughtherewasnothing particularly new about the Dye-Transfer process, the fact that Kodak promoted it made such an impact that it has still been run in 1990 yielding some of the best color prints ever made (the production was discontinued in 1993).The process:Three relief matrices were taken from separation negatives using specially preparedmatrixfilm.Thefilmwasexposedthroughthebaseanddevelopedin

Figure 42New York 1988 by Helen Levitt.

Figure 43Dyeing of the magenta matrix, rolling into contact with the final paper and removing the matrix after dye transfer.

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Throughout the 1920s and 1930s the conversion of silver images into colored metallic salts (metallic toning) led to the idea of superimposing three toned gelatin layers. The process was easy to operate but the toners didn’t yield colors as satisfactory as the dyes or pigments used for dye-transfer or carbon processes.4.2.7. The separable tri-pack

(Three separable film layers)

Longbeforeintegralmulti-layerfilmswereinvented,therehadbeenmanyideasofhowtouseaseparabletri-packoffilmsorplatesinanordinarycameratoobtain three separation negatives in one shot.

Themainproblemwithseparabletri-packsofanykindisthepoordefinitionresulting from light scattering as the image forming rays had to pass three emulsions and their supports. Another problem was the arrangement of the emulsions. With the usual sequence of recording (blue, green and red), the cyan record, providing most of the visual definition, was the least sharp.Reversing the recording (red, green and blue) would have asked for so much yellow dye in the emulsion for the red record, to decrease its blue sensitivity, that there would not have been enough blue light transmitted to record the blue image.

The idea of a separable tri-pack showed no commercial success.

In 1914, John Capstaff inventedthefirstKodachromeprocess,atwocolorprocess. It required an orange-red and a bluegreen record negative, which were developed and bleached in a solution to harden the gelatin in proportion to the silver present. Orange-red and bluishgreen positives were obtained by immersing the bleached plates in the correspondent dye. The two positives were bonded together (one of them having been reversed left to right) to yield a two-color transparent image. The process worked quite well for portraits, where the absence of blue is not too important, but it was only on the market forafewyears.However,inamodifiedversion,theprocesswassubsequentlyusedtoproducemotionpictures(firstTechnicolorprocesses).In the mid 1930s Kodachrome and Agfacolor, two multi-layer processes, replaced all additive and assembly methods of color photography, despite of the rather long success of the concept of an integral subtractive process.

4.3. Multi-layer processes

(Integral tri-pack)

The dyes were directly formed within the blue, green and red layers of the emulsion.

In 1905, Karl Schinzel published an article entitled ‘One Plate Color Photography’, the first clear suggestion to use a self-contained, triple layermaterial for color photography. His ideas were farseeing but he could not implement them.

Schinzel’s idea was to coat a plate with alternating layers of silver bromide emulsion and clear gelatin and to have each sensitive layer colored complementary to its sensitivity - a farseeing but unachievable aim at that time - and then, after exposure and development to treat the monopack with a

Figure 44First Kodachrome process.

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solution of hydrogen peroxide (bleaching) in the hope that the dyes would be decolorized wherever there was silver but not elsewhere, leaving a three color reproduction of the subject.

At that time it was almost impossible to apply multiple layers with the primitive emulsion coating equipment available.In 1907, Benno Homolka discovered some “true” color developers. He showed that colored images could be formed by the creation of dyes, in combination with the development of silver images, rather than by their destruction. He found colorless developing agents that were forming colors themselves wherever silver was reduced. The silver could afterwards be removed. Homolka could only produce few colors and there was no commercial use made of his discovery.

In 1911/12, Rudolf Fischer patented the application of Homolka’s work. In

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their articles and patents Fischer and his colleague Hans Siegrist outlined the basic chemistry involved in color development, comparable to du Haurons propheticpatents.Theywerethefirsttousetheterms‘colordevelopment’and‘color former (coupler)’ and their ideas provided the base of all processes of today.

Fischer proposed to add dye-forming substances (couplers) to three differently sensitive emulsions and then to coat them in superimposition. The couplers were selected so, that they formed a color, complementary to

claims, which he had applied for ten years earlier. Without going into details, he made clear that the controlled diffusion of processing solutions could provide a way of treating images differentially that have been formed at different depths within either a single or multi-layer emulsion. Troland preferred using a single layer emulsion that had been sensitized differentially by controlled penetration of sensitizing dyes considering the practical and economical problems of multi-layercoatinginthe1920s.HispatentwasfinallyacquiredbyKodak.4.3.1. Kodachrome (reversal film)

In 1923, Mannes and Godowsky, unaware of Troland’s ideas, patented a two-color subtractive process based on controlled diffusion. In 1925, when

Figure 46The two musician/inventors Leopold Godowsky (left) and Leopold Mannes, dubbed ‘man’ and ‘god’, photographed in the 1930s. The two considered photography a hobby and music their life’s real calling. It is said, that they were measuring the time in their experiments by playing a piece of music.

Figure 45Rudolf Fischer (1881-1957).

the corresponding sensitization of the emulsion. Reacting with the silver, the developer yields a very strong oxidation product. Absorbing the oxidation product, the coupler became colored (coupling of two colorless substances). When a screen negative was exposed to such a layer, a positive color image was formed after developing and fixing. The advantage to Homolka’s ideawas that a single developer could be used, reacting with the three couplers to produce three different dyes.Fisher also proposed to use a yellow colored layer between the blue sensitive emulsion and the two others (green and red) to reduce their sensitivity to blue light. But similar to du Hauron, Fischer could not realize all of his proposals.

At that time, the only couplers available diffused too much into adjacent layersandinadditionitwasdifficulttopreventsensitizingdyesfromwanderingbetween the layers.

In 1931, Leonard Troland was granted a patent of the impressive total of 239

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they bought a copy of E. J. Wall’s ‘History of three Color Photography’ because itcontainedareferencetotheir1923patent,theyheardforthefirsttimeaboutFischer and Siegrist’s work on color couplers recognizing immediately the potential of color development.In 1927, Mannes and Godowsky got a patent including the idea of selectively re-exposing a mono-layer emulsion by means of colored light, anticipating the later Kodachrome process.Starting in 1922, the two collaborated for 17 years with Eastman Kodak joining the research staff of Eastman Kodak in 1930. Mannes and Godowsky believed in the advantage of mono-layer, mixed grain coatings but they could not deliver any workable process when their contract was about to run out in 1933. It was the time of the Great Depression in the US and the two were afraid to loose their job. So rather than offering nothing they presented to Dr. Kenneth Mees (director of the Kodak Research Laboratories) a two-layer color development material and pleaded for more time to convert it into a three-color material.

In 1935, Eastman Kodakannouncedtheirnewfilm,calledKodachrome,animportant day in the history of color photography. It was a three-color version ofthefilmMannesandGodowskyhadpresentedtoDr.Meespreviously.

The original Kodachrome process by controlled diffusion bleaching (a direct positiveprocessyieldingslidesorfilm):

Figure 47 (see next page)Scheme of the very complicated processing of the film (28 steps were involved and the total processing time was 31/2 hours!).1) The silver negative images in all three layers were developed with a black-and- white developer.2) The developed silver and the yellow filter dye were removed by bleaching, and the positive images, composed of the remaining sensitive silver halides, were exposed to light.3) All three layers were redeveloped in a cyan dye forming color developer (the oxidized developer reacted with a coupler to form the cyan dye).4) The developed silver and the cyan dye in the two top layers were bleached (the silver was rehalogenized and the dye was destroyed). This was the key to the process and was known as controlled diffusion bleach. After bleaching, the film was exposed again.5) The silver images in the top two layers were redeveloped in a magenta dye forming color developer.6) The developed silver and the magenta dye in the top layer were bleached and the film was again exposed.7) The silver image in the top layer was redeveloped in a yellow dye forming color developer.8) All the developed silver was removed.

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Thefilmconsistedoffivelayers:1. Blue sensitive layer containing a yellow dye to absorb all blue light on top.2. Layer of clear gelatin providing a safety range for the controlled diffusion bleach.3. Blue and green sensitive layer.4. Layer of clear gelatin providing another safety range.5. Blue and red sensitive layer.In 1938, KodakintroducedasignificantchangeinprocessingtheKodachromefilms.Bythensensitizerswereavailablethatwouldremainintheirrespectivelayersandkeep theirsensitizingpropertiesafter thefirstdevelopment.Theblue sensitive layer could now be selectively re-exposed with blue light followed byyellowcolordevelopmentthatcouldnowpenetratethewholefilm.Thenthered sensitive layer was treated the same way using a cyan color developer. A fogging agent was used to make the green sensitive layer redevelopable. This meant that the precisely controlled diffusion of bleaching solutions was no longer necessary and the number of processing steps was reduced from 28 to 18. So far the diffusion of the substances falsifying the colors remained a problem.

Furtherchangesweremadeandin1961thefilmitselfwasredesigned(twoemulsion layers for each of the color records) and named Kodachrome II. The

one of the few projectors available at that time.In 1938, Henry Staehlepatentedthefirst35mmslidemountingservice,whichwas introduced by Kodak in 1939. The mounts were made from cardboard, a mountingmaterialthatwasusedforthenextfiftyyears.Kodak’sdecisiontointroduce a slide mounting service was crucial for the subsequent popularity of 35mm color photography.In 1938, Kodak introduced Kodachrome in cut-sheet sizes to satisfy large-format photographers who were not willing to convert to 35mm cameras. The production was stopped in 1955 because many professional photographers preferredthecut-sheetEktachromefilmwithits‘userprocessing’facility.

Right from the beginning, Kodachrome transparencies were far superior to any of the earlier additive processes. The emulsion layers were quite thin because

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Figure 49Projector for viewing uncut rolls of Kodachrome transparencies.

Kodachrome II had a speed rating of ISO25. In 1986 an ISO200 version was introducedbeingsometwenty-fivetimesfasterthanthefilmlaunchedin1935.

Atthebeginningtheprocessedspoolsoffilmwerereturnedtothecustomersas uncut rolls. They either viewed the results by hand or wound them through

Figure 50Kodachrome film returned in cardboard ReadyMounts.

Figure 51Kodachrome slide taken by Ella Maillard in Afghanistan, 1937/38.Left: Original, bleached slide. Right: Digitally restored version by IMC, see R.Gschwind and F.Frey, Journal of Imaging Science and Technology.

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the dye forming couplers were not incorporated in the emulsion (contrary to the couplers from Agfa). Within thin emulsion layers there was little light scattering, which gave a picture with high resolution. One of the shortcomings of the early Kodachrome was the impermanence of the dyes forming the images, however permanence was improved a lot after the introduction of the new Kodachrome process.

4.3.2. Agfacolor Neu (reversal film)

In 1935, Wilhelm Schneider, working for Agfa Filmfabrik, discovered by chance that dyes with long chain-like structures were less likely to diffuse through a gelatin layer. In 1936, I. G. Farbenfabrik got a patent for dye forming compounds resisting to diffusion. In 1936, Agfa introducedamulti-layer reversalfilmbeing influencedby the

Figure 52Wilhelm Schneider (1900-1980).

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Figure 54Diffusion of dyes in an early negative film.

Figure 53Agfacolor coupler with long chains form micelles, which can not diffuse any longer.

Figure 55Illustration of a magnified section of an unprocessed Agfacolor Neu film.

Figure 56Agfacolor Neu. Picture taken by Theodor Strübin in Liestal, 1940 (original and restored version like Figure 51).

introduction of Kodachrome in 1935 and the success of the lenticular movie-filmsbyPerutz.ThefilmwascalledAgfacolorNeutodifferfromtheAgfacoloradditive product that was still on sale. Agfacolor Neu had diffusion-stable color-couplers (“long-chain” couplers) in the corresponding layers, thus the processingofthefilmwasquitesimplecomparedtotheKodachromeprocess.After the War the factory at Wolfen found itself in the Russian-controlled zone and after 1954 all Agfa products made at Wolfen were renamed ORWO (Original-Wolfen).

OrwowasstillproducingAgfa-typecolorfilmsin1990,longafteralmost

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every other photographic manufacturer had accepted the necessity to produce colorfilmsthatwouldbecompatiblewiththeprocessingrequiredbyKodak.It seems likely that an Agfacolor negative/positive print process would have been established before Kodacolor was ready, had there been no separation of Wolfen and Leverkusen because of the War.Immediately after World War II, American and British experts visited the I. G. Farbenindustrie in Wolfen and Leverkusen to study the production methods and formulasofAgfafilmandpapermaterials (BIOSandFIATreport).Thepublication of the reports meant that any photographic manufacturer was free to produce its own versions of Agfacolor products. The companies that took advantage of Agfas know-how were: GAF (US), ICI (England), Ferrania (Italy), Valca (Spain), Tellko (Switzerland), Fuji/Konishiroku/Oriental (Japan). (See page 28).

In the 1930s, printing complementary colored negatives directly onto another to produce a positive print would have given unsatisfactory results because of the repeated use of imperfect dyes that were available at that time.

4.3.3. Kodacolor (negative/positive material)

and Ektachrome (slide)

In 1937, Michael Martinez got a patent protecting the incorporation of a color

from diffusing in the gelatin, assigning their patent to Kodak. It consisted of dissolvinghydrophobiccouplersinoildropletsandoffinelydispersingthesedroplets in the emulsion (like fat in the milk). During color development, the oxidized developer penetrated the oil droplet where it formed the chromogenic dye.Searching for improved dyes Agfa realized that a color negative does not have to be a recognizable reproduction of what was photographed.

BecauseoftheWorldWarIIitwasdifficulttoreturnthefilmsfordevelopmentback to Kodak. The Agfa couplers offered a great advantage because they werealreadyincorporatedinthefilm.ThereforeKodakwaslookingforawayto incorporate their couplers too, using the idea from Vittum and Jelly. This research led to the introduction of Ektachrome in 1946.

In 1942, Kodak launched theKodacolorprocess (colornegativefilm, color

Figure 57Illustration of a magnified section of a Kodacolor or Ektachrome film.

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Figure 59Scheme of the processing of a negative film.1) Color development of all three layers at the same time.2) Bleaching and fixing.

Figure 58Cross section of the emulsion of a processed negative film. From top to bottom:1) Blue sensitive layer containing yellow coupler.2) Green sensitive layer containing magenta coupler.3) Red sensitive layer containing cyan coupler.

coupler in a resinous binder and in 1940 he got another patent for a mixed grainmonolayercolorfilm.Kodakobtainedtherightstothepatentsbecausethey were very close to what they intended to do. The ‘protected’ couplers (Ektachrome)weresoeffectivethateverymanufacturerofcolorfilmsorpapersfinallyadoptedtheminthelate80s.In 1940, Paul Vittum and Edwin Jelly patented an idea to prevent the couplers

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negative print paper and corresponding development processes), the firstcomplete system of color photography using the Ektachrome type of coupler, thatwouldonedaybecomethenorm.TheoriginalKodacolorfilmhadaspeedof ASA25. It was a three-layer material using couplers that resulted in relatively unstable dyes.

BecausetheearlyprintsfromKodacolornegativefilmswerefarfromperfect,the contrast of the negatives had to be high to yield satisfactory color saturation in the prints. In 1944, a black and white image layer, in which a negative image was formed during development (negative silver mask), was added to solve the problem.In 1943, Wesley T. Hanson of Kodak patented the use of colored couplers for masking. Hanson’s patent has been summarized as follows:

Figure 60Left: Print from an unmasked negative. The blue is “blackened” and the yellow is “whitened”, caused by the side absorbtions of the dies. Right: Print from a masked negative.

Figure 61A 1946 advertisement for Kodacolor roll-film and prints. At that time most amateur photographers were using roll-film cameras and they were the people for whom the new process was intended. A 35mm version didn’t appear until 1958!

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Unmasked film. Orwocolor NC 16 (1967).

Figure 62Absorbtion curves of the dyes. A) Ideal curves. B) Actual curves showing the side absorbtions of the dyes that are canceled out by the masking couplers.

400 blue green red500 600 700

(wavelength)

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400 blue green red500 600 700

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Figure 64Mask of a negative. Magenta shows mainly side absorbtion in the blue, asking for a yellow mask. Cyan shows side absorbtion in the blue and green, asking for a reddish mask.

‘ To eliminate the necessity of using a separate mask for color correction, at least one of the dye layers has incorporated in it a dye, which cancels out the minor, unwanted colors absorbed. The dye is so chosen that, upon coupling, it changes to a complementary color of the main color former in the emulsion layer.’

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In 1946, Kodak launchedEktachrome,theirfirstcouplercontainingreversalfilmforuserprocessing.Theprefix‘Ekta’wasusedforfilmsbeingprocessedby the user. By 1990 there were some nine different versions of Ektachrome available, ranging in speed from ASA50 to ASA1600. Since 1976 all Ektachrome filmswereprocessedinE-6chemistry.In 1963, Kodak launched the Instamatic 126 camera and cartridges

Figure 65The Instamatic 126 camera.

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popularizing the use of Kodacolor films throughout the world. The camerawascheap,easytohandleandthefilmswereataspeed(ASA64)thatmadeit possible to obtain good results under a wide range of conditions. The introduction of the Instamatic 126 did more than any other development to bring color photography to the mass market.As the Kodachrome and Kodacolor films becamemore andmore popular,independentphoto-finisherscriticizedthatall thefilmshadtobereturnedtolaboratories established by Kodak. In 1955 the US Government required Kodak to ceaseselling filmswith thecostsof processing included,and toprovideprocessing formulas and know-how to other photo-finishers. While Kodakcontinued to offer processing services, their share of the business decreased strongly.

In 1972, Kodak introduced the Instamatic 110 camera and cartridges. The cartridgescontaineda16mmfilmmadepossiblebyasignificantimprovementinresolution.ThefilmwasrenamedKodacolorIIrequiringdifferentprocessingcalled C-41, which became standard for color negatives throughout the world. The improved resolution and better color reproduction resulted from a new form of color coupler, called DIR coupler. The C-41 process required now only 30min.

4.3.4. Further developments

Figure 66Ansco’s Printon process. Kodak’s research staff knew that they had to find an alternative way of incorporating couplers in emulsion layers to produce color films and papers that were as easy to process as the Agfa materials.

In 1938, Agfa-Ansco Inc. (USA) launched AnscoReversal film, a versionof Agfacolor Neu. The company was the result of a pre-war link between the American I. G. Chemical Corp. and the German I. G. Farbenindustrie. During theWarthecompanyproducedonlyfilmsformilitaryuse.AftertheWar,thefilmwasreleasedtothepublicunderthenameAnscochrome.In 1943, Ansco introduced a reversal color print material called Ansco Color Printon.ItwasthefirstdirectreversalprintmaterialtobebasedonAgfa’slong-chain couplers. In 1946, Ansco began to offer Printon material to individual

photographers.Itwasthefirsttimeamulti-layercolorprintmaterialcouldbeprocessed by the photographer in his own darkroom. The color balance of prints could be adjusted by inserting suitable combinations of yellow, magenta orcyangelatinfiltersintothelightpath,astherewerenospecialcolorheadsfor enlargers at that time.In 1949, Agfa (Leverkusen) introduced thefirstAgfacolornegativefilm.Butitwasnotuntil1952thattheyproducedtheirfirstreversalfilm,becausefilm

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research and production has been mainly done in Wolfen. Once the radical post-war reorganization calmed down, many improvements were made to Agfacolor products. In 1956, Agfacolor Negative had a speed of ASA40, beingnotfarfromthespeedofatypicalblackandwhitefilmofthattime,andAgfacolor Reversal Film had a speed of ASA50.During World War II many research chemists from Agfa escaped from the German regime and after the War several other research chemists left Agfa Wolfen. Many photographic manufacturers took advantage from this fact and from the transfer of knowledge by the BIOS and FIAT report.

In 1949, Ferrania (Italy)produced theirfirstAgfacolor-typenegativefilm. In1971, Ferrania was taken over by the 3M company and the names of their products were changed accordingly.

In 1951, Tellko (Switzerland) introduced Telcolor, basically an Agfa-type color negativefilm.ThefilmwasdevelopedwiththehelpofWilhelmSchneiderandAlfred Fröhlich, who had left Agfa Wolfen soon after the end of World War II. Telcolorcouldbeexposedeitherindaylightorartificiallightanditincorporateda silver image mask. In 1953, Telchrome was introduced, an Agfa-type reversal filmwithaspeedofASA50.In1960TellkowastakenoverbyCIBA.

In 1957, Imperial Chemical Industries (ICI, England) introduced a cut-sheet colornegativefilmcalledICIcolor.ItwasbasedonAgfacolor,incorporatingacoloredcouplerproducingamaskingimage,thefirstofitskindinEurope.In1959 ICI joined forces with Ilford Ltd. and ICIcolor was renamed Ilfocolor. By the end of the decade, Ilford gave up the amateur color market and concentrated on the production of Cibachrome.

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Figure 67Composition of the Ektachrome E100G/GX and E200 film. Modern films are made of up to fourteen layers and are about 30µm thick.

In 1962, Gevaert (Belgium) launched the Gevacolor-S slide film. It wasspecially designed for the US-market, asking for a development like the Kodachromefilms.ThethirdgreatestfilmproducerinEuropesecretlystartedtheresearchforacolorfilmaftertheexampleofKodachromealreadyunderGerman occupation.In 1987, Konika introduced a Konica Color negative film with a speed ofASA3200,theworld’sfastestfilmatthattime.

In 1990, FujiintroducedVelvia,acouplercontainingASA50filmforprocessingin E-6 chemistry, setting new standards of image sharpness. Before, Koda-chromefilmshadabetter resolutionbecause theyhadnocouplers in theiremulsion scattering the light.

Agfacolor material was incompatible with the Kodacolor material because it contained a different kind of coupler. The Agfa couplers had a long chain and the Kodak couplers were dissolved in oil droplets. By 1980, almost every manufacturer had accepted that they would have to offer color films andpapers requiring the same processing as Kodak’s coupler containing products (Kodacolor = C-22, then C-41 and Ektachrome = E-4, then E-6).

In 1950, Charles Barr and Keith Whitmore patented a class of new couplers. The so called DIR coupler (development-inhibitor-releasing). A DIR coupler, during the coupling reaction to form a dye, splits off a molecule that then inhibits further development. The benefitswere edge enhancement (highersharpness) and higher color saturation.

Themainproblem inproducingcolorfilmswas thescatteringof light in thethree layers. As all layers were sensitive to blue light, the yellow forming layer had to be on top of the emulsion and the cyan forming layer, contributing most to the picture, was on the bottom (the order of the layers can only be reversed

In the 1940s Konishiroku (later called Konica) and Fuji Photo Company launched Kodachrome-type products. But after the end of War, free information about Agfacolor persuaded Japanesemanufacturers to produce filmsandpapersbased on the use of long-chain couplers. In the 1950s, Oriental Photo Industry, FujiandSakurawerereadytolaunchtheirfirstAgfa-typefilms.In 1948, Ilford Limited introduced aKodachrome-type reversal film calledIlford Color D, after being engaged with the Dufaycolor additive process duringmostofthe1930s.Thefilmhadtwo‘barrier’layersthatwereconvertedinto silver in the first developer so that theouter and inner layers couldbesuccessively and separately re-exposed (from the top and the bottom) and colordeveloped.In1962thefilmwasrenamedIlfochrome,andbecausetherelevantpatentsofKodakhadexpired,thefilmcouldbeselectivelyre-exposedin the same way as Kodachrome. It’s production was stopped in 1965.

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inpaperemulsions,whichwasfirstdone in1954 for theKodacolorType IIIpaper).Theonlyalternativetoimprovethefilmperformancewastoreducethethickness of the emulsion layers. An additional problem was that the lowest emulsion got about 4-9 times less light than the one on top. The overcoming oftheseproblemsledtotheverycomplicatedcompositionofnowadaysfilms.4.4. Diffusion process

(one step color photography)

‘The story is by now well known and too good not to be true. Apparently, Land an amateur photographer, was taking family snaps at a picnic in 1943 when his young daughter demanded to know why she couldn’t see the pictures - “now”. She had picked on the right father to confront with that question.’Geoffrey Crawley, ‘The British Journal of Photography’ April 1968.

In 1947, Edwin LanddemonstratedthefirstPolaroidprocess,whichyieldeda sepia monochrome print within 60sec. The basic principles of the diffusion

Figure 68Edwin H. Land (1909-1991) a physicist and inventor.

process were introduced by Edith Weyde at Agfa in the 1930s. Shortly after, thefirstPolaroidLandcamerawaslaunchedundertheslogan”snapit,seeit’. Land has founded the Polaroid Corporation in 1937. The company’s original dominant market was in polarized sunglasses, an outgrowth of Land’s self-guided research in polarization.EdwinLandwasthefirstpersontodeviseaprocesswith incorporatedpro-cessing chemistry. He invented the principle of keeping the development re-agentsinviscousforminasmallpodattheborderofthefilm.Whenthefilm

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Figure 69Howard G. Rogers.

was pulled out of the camera, the pod was squeezed between two rolls ruptur-ing it. This allowed the reagents to spread between the surfaces of an exposed emulsion layer and an image receiving layer. The result was a practically dry process. Land was aware of the importance of color because the work that led tothefirstPolacolorprocessbeganalreadyin1948.

4.4.1. The Polaroid process

opaque film base

blue sensitive emulsion layeryellow dye/developer layer

green sensitive emulsion layermagenta dye/developer layer

red sensitive emulsion layercyan dye/developer layer

viscous alcaline solution

layer fixing the dyes

neutralizing layertiming layer

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receiving sheet

After exposure, while the film is pulled out of the camera, the viscous activating solution and the receiving sheet are auto-matically put in contact with the negative forming element.

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Figure 70Scheme of the layers of a Polacolor and the way they are put together.

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In 1963, Polaroid presented Polacolor I invented by Howard C. Rogers, head of thecolor researchofPolaroid. Itwas thefirstphotographic ‘on thespot’color process. The Polacolor process used a new kind of molecule to link the developer with an azo dye.PolacolorI,aseparablefilm/paperbipack,wasformedasfollows:The process:Afterexposure,thefilmwaspulledoutofthecamera.Duringthisact,apodcontaining an activator, a viscous alkaline solution, was squashed and a re-ceiving sheet was squeezed on top of the negative image-forming element. The dye/developer being easily soluble in the alkaline solution was released from the pod and started do diffuse to the exposed silver halide layers. When developing exposed silver halides, the dye/developer oxidized and remained stationary. The unoxidized dye/developer diffused to the receiving layer to yield a positive subtractive image. The agents in the uppermost layer of the receivingsheetfixedthedyes.Thewholeprocesstookabout50sec.

Polacolor was a ‘peel-apart’ system that could be used in most of the Polaroid camerasofthattime.Thefinalimagehadtobepeeledawayfromthefilm,onwhich the original camera image had been recorded. At room temperature the speedofthefilmwasaboutASA64.Commercialsuccessquicklyfollowedtheintroduction of the process and one year later Polaroid was the second largest photographic company in the world.Kodak produced the multi-layer negative elements of the Polacolor I system, while the receiving sheets were made by Polaroid themselves. When Kodak shareholders became aware of Polaroid’s success they wanted an ‘instant’ process of their own. In 1969, Kodak announced to enter the market them-selves forcing Polaroid to produce the negative elements on their own.

In 1972, Polaroid introduced the entirely new SX-70 system, which was an immediate success.

TheSX-70 filmwas amonopack. The negative image-forming elementand the receiving layer built one part. The paper base was transparent so that exposinglightcouldenterfromthetop.Afterexposure,thefilmwaspulledoutofthecameraand,apodatthesideofthefilmwassquashedinjectingtheac-

tivator between the receiving sheet and the negative image-forming element. Immediately a dark pigment was formed in the layer of the activator hiding the negative image. During development, the dark protecting layer was discolored and a white pigment (the white base for the resulting image) was formed. De-velopment took place like with the Polacolor I but with a new metallized dye/

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Figure 71Vocalist Grace Slick taking pictures, photographed by Roger Ressmeyer in 1976.

Figure 72The image begins to appear about one minute after the print emerges, but does not reach completion until some five or ten minutes later.

Figure 73Polaroid SX-70 camera yielding color prints in full daylight.

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developer. Processing (outside the camera) took between 5 and 10min.Land described the SX-70 camera as follows: ‘The photographer, after com-posing and focusing through a new kind of single-lens-reflex viewer, touches an electric trigger. Within 0.4 second of the shutter closing, from the front of the camera the picture emerges; it is hard, dry, shiny, flat and invisible. Over the next two minutes an image materializes providing a full color picture.’Theprintshadawhiteborderandanimageareaof8cmx8cm.Thefilmpackcontained 10 exposures and a battery (the camera itself required no batteries). Thecamerawasavailablewithauto-focusfacility,thefirstofitskind.

Stimulated by the success of Polaroid, Kodak wanted to complete the research of their own process. It was not an easy task to shirk the 1600 patents of Po-laroid.

In 1976, Kodak launched their own ‘pull-apart’ system. Their process was very similar to the one from Polaroid. The main difference was in the silver halide emulsions. With these emulsions, the unexposed grains could be developed, making it possible to produce positive images directly (direct positive emul-sion).

Sixdays later,Polaroidfiledanactionclaiming$12billions for lossofsalesand royalty payments that would have been due under a licensing agreement. Ten years later, Kodak was forced to withdraw their instant cameras from the market.In1990EastmenKodakhadtopayabout$900millionbuttheamountwas smaller than Kodak had feared. This was one of the largest settlements in American legal history.During the 1970s and 1980s Polaroid introduced several inprovements to the SX-70system,amongthemTime-Zerofilm,whichreduceddevelopmenttimeto about one minute.

In 1986, Polaroid launched a color process, based on additive principles, calledPolaChrome.Afterrewinding,theexposedfilmwasprocessedoutside

Figure 74Self-portrait with skull by Andy Warhol, 1977.

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the camera in a machine called AutoProcessor. It produced 35mm color trans-parencies ready for projection in less than 5min. after exposure. The Pola-Chrome was certainly not equal in quality to the subtractive color transparency filmsbutitofferedthepossibilitytoproduceslidesonthespot.

In 2003, Polaroid stopped the production declaring bancruptcy.4.5. Photofinishing

In 1955, Kodak was obliged to sign a Consent Decree under Anti Trust Law (seepage27).TheywererequiredtosellKodachromefilmswithoutthecostofprocessing included and they had to release both Kodachrome and Kodacolor processing formulas.Thiseventopened themarket to independentphotofi-nishers and Kodak’s share of the business decreased strongly.

Fromthe1970son,mostpeoplesenttheirfilmstophotofinishersandgotbacktheprocessedfilmsandprints.Thiswasfirstdonebysmallcompaniesandlater by large-scale central laboratories operating by mail-order. After 1980, mini-labs appeared in the high streets and shopping malls of the world.

4.5.1. Printing from color transparencies

Although color reversal filmspreceded color negative films, theymust nowbe seen as something of an anachronism in the history of popular amateur photography. There were many problems to be solved before a reliable and cheap color print could be made. That is why the color transparency achieved such popularity among amateurs after the introduction of Kodachrome and Agfacolor in 1935/36. From the manufacturer’s point of view, the advantage of producingareversalratherthanacolornegativefilmoutweighedthefactthattheywereofferingtheamateurafilmwithaveryrestrictedexposurelatitude.

In 1941, Kodak introduced a reversal print material because many amateurs requiredcolorprintsfromtheirslidesandtheyestablishedtheworld’sfirstcolorprinting service. The prints were made on a white pigmented acetate base. There were two materials called Minicolor (for 35mm slides) and Kotavachrome (forsheetfilms)recognizablebyroundedcorners.TheMinicolorprintswereenlargedeither2x for75centsor5x for$3.50and in1945,some4millionprintsperyearweremade.AftertheintroductionoftheKodacolornegativefilmin 1942, Kodachrome prints were no longer popular.

In 1943, Ansco introduced a reversal color print material called Printon. The emulsionwasappliedonawhite-pigmentedfilmbasejustlikeKodak’sprints.Unlike Kodak, Ansco decided not to establish a processing service under their

control. But with their help, the Pavelle brothers in New York established and operatedacolor laboratorycalledPavelleColor Inc.Theybecame thefirstindependentcolorphotofinisherswithamodern laboratorywith large,high-speed continuous print processing machines. In 1954, the printers incorpo-rated automatic density integration but color balance and the necessary cor-rections were determined after visual examination. Also the Printon prints had rounded corners.In 1955, KodakproducedtheirfirstcolorprintsfromtransparenciesinEurope.Thematerialtheyusedwasthefirstpaperbasedreversalcolorprintmaterialand it employed color couplers of the Ektachrome type. The research leading

Figure 75A Kodak Minicolor print (left) and a print made by Pavelle Color Inc. on Ansco Printon material both made in 1954.

Figure 76The Pavelle color printers were operated in white light using Ansco’s direct reversal Printon material.

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Figure 77Scheme of a silver dye-bleach (SDB) process:1) After exposure, the silver negative images in all three layers were developed with a black-and-white developer. During the development any dye close-by the negative silver image was reduced, resulting in splitting of the dye molecules into colorless compounds.2) The silver image was bleached and the colorless dye compounds were washed out.3) The residual silver halides were fixed thus leaving directly a positive image.

toitsproductionwasmostlydonebyKodakPathéinFrance.

Attheendofthe1990s,colorprintersinphotofinishingwerebecomingdigital,i.e. the images (negatives and slides) were digitized and printed on negative print material, which is much cheaper. Today the best method to get prints from transparencies is to digitize them and then to expose the data on negative material because it has a better color reproduction than positive print material.4.5.1.1. The silver dye-bleach (SDB) process

In 1918, Jens Hermann Christensen got a patent about the catalytic reduction of dyes, the actual basis of the silver dye process.

In 1933, Bela Gaspar producedthefirstmotionpicturefilmsonGasparcolor,asilver dye-bleach process material. One of his most important discoveries was that the silver dye-bleach reaction could be highly accelerated by the addition of catalyzing organic compounds. Between 1949 and 1952, he operated a print making service using Kodachrome transparencies as originals. By this time his print material was called Gaspacolor Opaque. The process required particularly long exposure times and could therefore only be used for cartoon

Thefilmconsistedofthreelayerswiththeazodyesincorporated:1. Blue sensitive layer containing the yellow dye.2. Green sensitive layer containing the magenta dye.3. Red sensitive layer containing the cyan dye.Advantages of the process:Scattering of light, which is inevitable in silver halide emulsions, is considerably suppressed by the dyes in the emulsion thus improving the sharpness. Azo dyes used in the silver dye-bleach process are much more stable than any dyes formed by color development. The silver dye-bleach process produces colors of high purity, since no colored by-products arise in processing.

Disadvantages of the process:The dyes in the emulsion reduce the sensitivity of the material by about 10-100x times. The loss in speed is the reason why it has never been possible to produceacameraspeedSDBfilm.

In 1952, Ilford established their print-from-slide laboratory using a silver dye-bleach material for the prints, obtaining the necessary azo dyes from Geigy. In 1958, CIBA decided to intensify work on the silver dye-bleach process andtodiversifyintothephotographicindustryinasubstantialway.Theyfirsttook over Telko in 1960 and in the following year they bought Lumière. CIBA started contact with Ilford Limited in 1963 and by 1967 they had taken over the company.

With their printer, Ilford was able to make more than 1’000 exposures an hour,

Figure 78Cibachrome print exhibited at the Photokina in 1963.

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or puppet subjects or as a print out material.

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despite the extremely low speed of the material. For a decade they produced about a million prints a year before the color negative/positive process became popular.

In 1959, Armin MeyerfromCIBArealizedthefirstCibachromeprint,basedon the silver dye-bleach process. The three layers containing the dyes were coatedontriacetatefilmwhosebackwaspaintedwhiteafterprocessing.By1962,whitepigmentedtriacetatefilmwasbeingused.Initiallytheprocessrequired45minutesoftreatment.ThefirstCibachromematerialshadaverylow sensitivity, a characteristic of all early silver dye-bleach materials.

In 1969, Cibachrome Transparent (CCT) was introduced to display large transparencies that would not fade under the necessary back-lighting. At that time all other chromogenic print materials were based on color development yielding rather unstable dyes. Because printing was done from positive transparencies, itwasdifficult to keep thecontrastof theprintmaterial lowenough, a problem that was solved during the 1970s.

In 1974, Cibachrome-A for the amateur was introduced with processing timereducedandchemistrysimplified.Thenewprocessgainedwidespreadpopularity during the late 1970s and early 1980s because making color prints from transparencies was much easier for the amateur than printing from negatives.

Improvements in photofinishing services and color negative films, includingthe introduction of mini-labs, persuaded amateurs to change to the color

negative process. In 1989 Ciba-Geigy sold their photographic interests to the International Paper Company renaming their SDB-products Ilfochrome.

As an alternative to the SDB process, Kodak offered a color internegative material, with which masked color intermediate negatives could be made from transparencies before being used to produce color prints on a negative/positive paper.4.5.2. Printing from color negatives

In 1942, Kodak launched theKodacolorprocess,being thefirst toprocesscolor negatives from amateurs. With this introduction, color photography really began to reach the mass market.

The method of making a color print was to give a processed negative to an expertwhojudgedwhatcombinationoffilterswasrequiredinacolorprintertocorrect the overall hue of the negative. Since the judging step was time con-suming,itwascustomarytojudgeonlythefirstpictureapplyingthecorrectiontotheentirerolloffilm.Thenthefilmwasreturnedtotheoperatoroftheprinterwithacodeforthefiltercorrectionsonthefilm.

In 1947, C. M. Tuttle and T. B. Brown from Kodak patented the Kodak 1599 Figure 79Prints made from roll-film Kodacolor nega-tives produced in Eastman Kodak’s Roches-ter laboratory. Between 1942 and 1955, all Kodacolor films exposed in the USA were printed on 1599 printers.

printer incorporating the ideas of Evans (see next page). Each picture was integrated to grey, which was a big advantage to the previously known meth-ods where only one on each roll was judged. The printer exposed three rows of prints along a 28cm web of paper. Each print was successively exposed throughblue,greenandredfilters,aprocedurewhichbecameknownasaddi-tiveprinting.The1599printerwasofferedforsaletootherphotofinishersbutit

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was too complex and expensive.In 1954, Kodak introduced Kodacolor Type III paper. The layers of the new paper were arranged with the red-sensitive layer on top (as the cyan forming layer contributes most to the picture) and the blue-sensitive layer next to the paper base. In 1986, Kodak introduced their Ektacolor 2001 paper and RA-4

Figure 81Agfa Varioscop 60 enlarger. The first enlarger to incorporate continuously adjustable color filters.

Figure 80Kodak S1 printer with white light printing by subtractive termination.

chemistry, after which a color print could be processed and dried in a little over 4 minutes.In 1967, Kodak introduced the S1 printer designed by R. W. G. Hunt. Blue, greenandredexposureswereobtainedbytheinsertionofsubtractivefiltersintowhitelight.Itwasthefirstprintertouseasinglewhitelightexposureratherthan successiveexposures throughblue, greenand red filters.Most of the

printers that followed adopted this method.Therewasabigdifferenceinphoto-finishingbetweenKodakandAgfa.Kodakdesigned special printers, on which they made large numbers of print expo-sures using long rolls of paper that were processed continuously before being cut into individualprints.Agfa tended to leavephoto-finishers toadapt theirblack and white equipment. Corresponding color correction was achieved by introducingsubtractivecoloredgelatinfiltersintotheenlargingbeam.In 1958, Agfacolor negative/positive materials for user processing were released and soon after, improved methods of print exposure and processing were devised. First Agfa designed a color lamphouse for use with their Varioscop enlargers.

In 1969, Keith Astoninventedtheintroductionofsmalldichroicfiltersbetweena focused quartz-halogen lamp and a light mixing chamber. This arrangement wasusedbyPavelle(laterDurst)andwassoefficientandcompactthatmanyothermanufacturersbegantousedichroicfilters.

Withall theprecedentsystemsofcolorprinting,exposuretimeandfiltrationhadtobefiguredoutbymakingtestprintsfromastandardnegative.

4.5.3. Automatic methods of color printing

Because of low speed and limited exposure latitude, the chance for an ama-teur to obtain good color prints from every exposure was low. It was the deci-sionofthephotofinisher,whichnegativeshouldbeprinted.Hehadtoweighthe customers willingness to pay for a poor print against his wish to have some returnforthemoneyhespentonthefilmandit’sprocessing.

In 1938, F. H. G. Pitt and E. W. H. Selwyn of Kodak observed that the overall color of the average outdoor subject is nearly grey and that different subjects do not vary markedly from the average.

In 1946, Ralph Evans of Kodak patented the concept of arranging that the same total amount of red, green and blue light reached the print material (integration to grey) whatever negative was being printed.

The concept of integration to grey failed according to abnormalities of color distribution in the subject, causing some 10 to 20 per cent of prints being unacceptable. A frequent failure was any landscape scene with a large area of bright green grass in the foreground, giving rise to clouds tinted with magenta. As manufacturing and processing consistency improved, printer corrections were reduced and subject anomalies became less serious.

In 1956, V. R. Pieronek, W. L. Syverud and W. F. Vogelsong were the

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first todescribe theprinteradjustment called slopecontrol.Twoeffects ledto the necessity of slope control adjustments for automatic color printers: The reciprocity failure of the paper and the difference in spectral sensitivity between paper and monitoring photocells.

Now, color enlargers could be linked to electronic analyzers that were used to evaluate a color negative before it was printed. Macbeth, Speedmaster, Lektra and Melico were among the many companies producing analyzers that allowed judgingandadjustingthefiltrationofanegative.Inallcasestheanalyzercouldonly be set up after making test prints from a standard negative to determine thestandardfiltration.

In 1961/62, Ilford Limited decided to produce a contact print from every 35mmfilmtoleavetheselectionofthenegativesthatshouldbeprintedtothecustomer. After contact printing the negatives were cut and card mounted and then, together with the contact print, sent back to the customer. Then, the cus-tomer returned the selected negatives for enlargement printing. The contact prints and mounted negatives were very popular. But the Monopolies Commis-sion in the UK ruled that Kodak and Ilford must reduce the prices of their color films,whichforcedIlfordin1968towithdrawfromtheamateurmarket.

In 1963, Kodak introduced an entirely new cartridge loading system of snap-shot photography. The success of the system was undoubtedly based on the salesofKodacolorfilmsandit isprobablethattheintroductionof theInsta-matic126systemdidmoretopopularizecolornegativefilmsthananyothermarketing program.

Showinginstantaneouslytheeffectoffilteradjustmentsontheprintedpositive,video analyzers have been first used bymotion picture laboratories. Three

Figure 82The Bremsons CVIS, Digital Video Analyzer allows four different reference images to be shown at the same time.

graduated control knobs enabled the operator to vary color balance and brightness of the video image, until he has been satisfied. The final scalesettingsindicatedthefiltrationrequiredtomaketheprint.

In 1969, Kodak introduced a Video Color Analyzer (VCNA) that was used by motion picture and professional photo laboratories. After that, the use of video analyzers became widespread.When resin coated paper became available (around 1970), roller processing machines began to be used for color prints. The sheets of paper were moved from solution to solution by a series of closely spaced rotating rollers. Resin coated paper was protected on both sides by a layer of polyethylene leaving only the emulsion to absorb water. Now, color paper processing could be completed in less than 10min.

Photofinishers in Europe had to deal with two different color negative pro-cesses,oneforAgfacolorandoneforKodacolorfilms.Thisproblemwasnotsolveduntil1978,whenAgfadecidedtoproduceonlycolorfilmsandpaperthat required processing in the C-41, E-6 and EP-2 chemistries established by Kodak.

In 1972, Kodak obtained a patent for their multi-scanning idea. For subjects, in which one color predominates, the ‘integrating to grey’ correction resulted in unacceptable color mistakes. The idea was to scan the whole length of each filmbeforedealingwiththeindividualframes.Measuringforallpicturestheav-erage intensities and then integrating to grey provides a better color correction

Figure 83Gretag’s scanning printer read blue, green and red transmissions at approximately 100 different points of a color negative.

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than integrating each single picture.

In 1974, Gretagintroducedthefirstcolorscanner.By1976theyhadincorpo-rated a color scanner in the 3140 printer, designed by Walter Grossman, that was capable of exposing some 5’000 prints an hour. The scanner used a rotat-ingaperturedisctogetherwiththreefilteredsiliconphoto-cells.Laterafixedarrayoffibre-opticdetectorswasusedinsteadoftherotatingdisc.The introduction of scanning to determine the exposure required for a par-ticular negative, made it possible to operate printers at very high speeds with-

Figure 84Kodak’s CLAS 35 printer was designed for very large photo-finishing laboratories. It had an output of some 20’000 prints per hour and was able to scan each negative with 864 points per frame.

out any attention from an operator. In 1983, Agfa, Fuji and Kodak introduced new scanning printers. The Agfa printer incorporated the multi-scanning idea andwasabletodetectnegativesthatwereoutoffocus.Thefilmpassedfirstthrough a scanning station before being printed frame by frame. Fuji’s Advance ComputerizedColorScanner(ACCS)wasthefirsttouseachargecouplede-vice (CCD) to recognize image patterns. To determine the main subject in the photo, the ACCS software consults an amount of simulated image patterns.In 1986, Agfa demonstrated a print system based on a high resolution scan-ner to digitize transparencies and then electronically reverse them. Afterwards the data were written by a three color cathode ray onto negative paper. This procedure allowed to control contrast, which was always a problem of taking prints from transparencies.

Despite their investment in large and expensive printers they were all aware of the growing importance of the mini-lab.

In 1978, Noritsu, a Japanese equipment manufacturer, exhibited a complete laboratory thatwas able to accept 35mm films and to deliver prints in just45min. They called the system Quick Service System (QSS). They believed that thewhole photofinishing cycle could be carried out on-the-spot.Whatmade the idea possible was the steady reduction in the processing time of filmsandpaperandimprovementsintheautomaticdeterminationofexposure.In 1982, Ilford introduced the Cibachrome Print Centre, a daylight operating enlarger/processor, which enabled the user to visit his local photo dealer and while there, to make selective enlargements from his own color transparencies. The print material was Cibachrome and the time required was 10 minutes.

In 1984, S. Kobishi and M. Kurematsu got a patent protecting a method of processing color papers, in which washing is replaced by a treatment with a stabilizing solution. Soon after almost every manufacturer of mini-labs was of-fering washless processing as an option.

In 1988, Kodak introduced the Create-a-Print Centre. It was a stand alone enlarger/processor, intended for the customer to produce selectively composed enlargements from 35mm color negatives. Composition and color balance could be examined on a monitor and only when the video image appeared

Figure 85The Gretag Master Lab.

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satisfactory, the exposure was initiated. Finished prints could be delivered in four minutes.

In 1989, Gretagproducedthefirstfullyintegratedmini-labcallingittheMasterLab. It incorporated filmprocessor, printer andpaper processor in a singlefree-standingunitrequiringnomorethanonesquaremeteroffloorspaceandno connection to running water or a drain.5. Coating techniques and drying

Early coatingmachines laid down one emulsion at a time.One of the firstmethods of coating long length of film or paperwith emulsionwas by ‘dip’application and ‘festoon’ drying. The immersion of one side of a moving web offilmorpaperinaliquidemulsionwascalleddipcoating.Thismethodgaveway to the ‘kiss’ coating, whereby a rotating roller picked up emulsion from a trough and transferred it to a moving web. Neither of these methods allowed accurate coating.

Much more precise coating became possible with the introduction of ‘slot’ coating. The method ensured a predetermined volume of emulsion to be

wasahighlyeconomicalmethodofdryingfilmsonalargespiralinthedryingchamber. Towards the end of World War II, Agfa built a high speed single layer coatingmachinebasedontheuseofalargedrumsupportingthefilmwhilehot

Figure 86Figure from Russell’s patent.

pumped through a slot onto the web to be coated. However the coating speed was slow (< 15 m/min).

In 1887, A. J. Boult invented the festoon dryer selling the rights to George Eastman.Thefilmorpaperwashunginloopsoverpoles,whichwerecarriedby a track through the drying chamber. Film or paper coated on a festoon machine often had characteristic ‘stick’ marks, resulting from inhomogeneous drying.Two methods to avoid ‘stick’ marks were the spider drying or the use of machinesincorporatinga‘straightaway’or‘flat-bed’section.Thespiderdrying

Figure 87Schematic representation of a curtain coating machine.

Figure 88Diagram of a festoon drying track.

Figure 89View down a festoon drying alley.

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air was blown across it in the opposite direction of its travel.

In 1951, Albert E. Bequin of Kodak obtained a patent describing a method of applying reduced pressure on the underside of the emulsion bead to hold it in contact with the web at high coating speeds.In 1956, Theodore A. Russell patented a cascade coating method, called slidehoppercoating,withthefirstmulti-layercoatingbeadandcoatingspeeds

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up to 100 m/min.In 1968, J. F. GreillerofKodakpatentedthefirstcurtaincoatingmethodforasingle emulsion layer.

In 1970, D. J. Hughes of Kodak patented a multi-layer curtain coating method. It offered the possibility of coating speed up to 200 m/min., the ability to coat over splices and freedom from pencil lines resulting from dirt particles trapped in the coating gap.By the 1980s the major manufacturers were coating color products requiring as manyasfifteendifferentlayerswithanaveragethicknessof0.001mm,addinguptothethicknessofemulsionofanaverageblackandwhitefilm.Thecoatingof multi-layer color material must be seen as an engineering achievement of thefirstorder.

6. The introduction of digital cameras

‘We all know it won’t be long before we can take pictures on a disc tape and view them straight away on a TV screen. There will be no need for processing. You will be able to enlarge or reduce the size of the image, change the color, add special effects - all at the touch of a button. If you think this is light years away, let me assure you it isn’t. Within two or three years, at least one system will be available if not more.’‘Amateur Photographer’ July 13th 1985.

In 1969, W. S. Boyle and G. E. Smith of the Bell Laboratories invented the charge-coupled semi-conductor device (CCD).

In 1973, Fairchild ImagingintroducedthefirstcommercialCCD-chipwitharesolution of 100 x 100 pixels.

In 1975, Steven SassonfromKodakbuiltthefirstdigitalcameracontainingthe Fairchild-CCD chip. Kodak didn’t recognize the potential of their invention and stopped further research on digital cameras. However, the steady loss of analog photography was induced.Some of the problems involved in achieving color separation with a CCD-chip were similar to those faced by the inventors of the early additive screen plates as the photosensitive surface has to be divided into blue, green and red components.

In 1990, Kodak announced to introduce a Photo CD system to digitize color negatives or slides and transfer them onto a compact disc (CD) in collaboration with Philips. The resulting CD was used to be viewed on a TV screen or to provide prints via a thermal transfer printer.

Nowadays there are a number of ways to obtain a color print via electrical signals without a silver-based print material. Among them are ink-jet printing, electrostatic printing and the thermal transfer process. The market for color prints nevertheless remains the only big market share of today analogue photography(exceptmoviefilms).

By the end of the 20th century, the viability of most silver-halide based color processes came under serious threat by the emergence of professional and consumer-level digital cameras and printers. According to an estimation of the ‘Photo Marketing Association International’ of February 2005, 20,5 million digital cameras were sold in the USA, compared to 4,6 million analog cameras, reaching a market share of more than 80%. The introduction of new photographic devices, like mobile phones with cameras, or the development of the internet will speed up the replacement of analog photography.

Figure 90The first digital camera with CCD-chip, hold by Steven Sasson, its constructor.

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ReferencesBellone, Roger / Fellot, Luc: histoire mondiale de la photographie en couleurs. Coulommiers:HachetteRéalités,1981.Coe, Brian: Colour Photography. Cambridgeshire: Balding + Mansell, 1978.Coote, Jack: The Illustrated History of Colour Photography. Surrey: Fountain Press, 1993.Friedman, Joseph S.: History of Color Photography. Boston (MA): American Photographic Publishing Company, 1947.Koshofer, Gert: Farbfotografie Band I-III. München: Laterna magica, 1981.Ostroff, Eugene: Pioneers of Photography.Springfield(VA):SPSE,1987.Rosenthaler, Lukas: Archivierung im digitalen Zeitalter, 2006.R.Gschwind and F.Frey: Electronic Imaging, a Tool for the Reconstruction of Faded Color Photographs. Journal of Imaging Science and Technology, 1994.Imaging & Media Lab (IML)

Figure 35: Bellone / FellotFigure 36: www.laputanlogic.comFigure 37: www.corbis.comFigure 38: CooteFigure 39: www.eastman.orgFigure 40: CooteFigure 41: KoshoferFigure 42: www.laurencemillergallery.comFigure 43: CooteFigure 44: CooteFigure 45: KoshoferFigure 46: Koshofer (up), www.corbis.com (left)Figure 49: CooteFigure 50: CooteFigure 51: Ella Maillard (left), Gschwind (right)Figure 52: KoshoferFigure 53: www.simscience.org/membranesFigure 54: Jenni, AWPFigure 56: Museum.BLFigure 58: KoshoferFigure 60: IMLFigure 61: CooteFigure 63: KoshoferFigure 64: IMLFigure 65: CooteFigure 66: CooteFigure 67: www.kodak.comFigure 68: www.corbis.comFigure 69: KoshoferFigure 71: www.corbis.comFigure 72: CooteFigure 73: CooteFigure 74: www.corbis.comFigure 75: CooteFigure 76: CooteFigure 78: CooteFigure 79: CooteFigure 80: CooteFigure 81: CooteFigure 82: CooteFigure 83: CooteFigure 84: CooteFigure 85: CooteFigure 86: CooteFigure 87: CooteFigure 88: CooteFigure 89: OstroffFigure 90: www.wikipedia.org

Sources of the figuresFigure 01: KoshoferFigure 02: CoeFigure 03: www.photohistory-sussex.co.ukFigure 04: CoeFigure 05: Bellone / FellotFigure 06: Bellone / FellotFigure 07: www.nobelprize.orgFigure 08: www.elysee.chFigure 09: CoeFigure 10: KoshoferFigure 11: CooteFigure 12: CooteFigure 13: KoshoferFigure 14: CooteFigure 15: OstroffFigure 16: www.corbis.comFigure 17: www.corbis.comFigure 18: CooteFigure 19: Coe (left), Koshofer (right)Figure 21: CoeFigure 22: www.corbis.comFigure 23: IMLFigure 24: CooteFigure 25: CooteFigure 26: CooteFigure 27: CooteFigure 28: CooteFigure 29: KoshoferFigure 30: KoshoferFigure 32: IMLFigure 33: KoshoferFigure 34: Ostroff

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