Modern Chemistry of the Ancient Chemical Processing of...

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Chapter 7

Modern Chemistry of the Ancient ChemicalProcessing of Organic Dyes and Pigments

Zvi C. Koren*

The Edelstein Center for the Analysis of Ancient Artifacts,Department of Chemical Engineering,

Shenkar College of Engineering, Design and Art,Ramat-Gan 52526, Israel*E-mail: [email protected]

The ancient dyer was an advanced empirical chemist. Whileinorganic pigments produced magnificent colors, the mostelaborate chemical processing of colorants in antiquity –from the source to the final product – involved organic dyesfrom flora and fauna sources. Towards this end, the dyerapplied his – or her – practical chemical knowledge to botany,entomology, and malacology. By controlling the temperatureand the alkaline or acidic pH of the dye bath, the dyers wereable to create colorful textile dyeings with some surviving evenafter six millennia. In order to produce stable products, theancient dyer mastered the methods that are based on advancedchemical topics, such as, ionic, covalent, and intermolecularbonding, coordinate complexation, enzymatic hydrolysis,photochemical chromogenic precursor oxidation, anaerobicbacterial fermentative reduction, and redox reactions. Thispaper discusses various chemical principles that were appliedby the ancient master of colorful chemistry.

© 2015 American Chemical Society

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In Chemical Technology in Antiquity; Rasmussen; ACS Symposium Series; American Chemical Society: Washington, DC, 2015.

Introduction: Historical Overview

Two decades have elapsed since the first paper on the subject of ancient NearEast dyestuff sources was published in an ACS Symposium Series by this author(1). In that work, emphasis was given to the yellow, red, and blue colorants thatwere obtained from flora dyestuff sources and the molecular structures of theirmain dyeswere discussed. In the last two decades, more analyses of archaeologicaldyes have been performed with greater emphasis on the more important faunaorigins of the red dyestuffs from scale insects and the purple and violet pigmentsfrom sea snails. This current paper, besides being a continuation and update of ourknowledge in this field, focuses on the ancient dyer’s advanced level of controland the highly complex chemistry applied in the process.

A number of classical English-language books have treated the history oforganic dyes and pigments from botanical, entomological, and malacologicalsources used in ancient times. Some of the more prominent texts discussingthese flora and fauna dyestuff sources include, chronologically, the works ofLeggett (2), Forbes (3), Robinson (4), Brunello (5), and Sandberg (6, 7); andmore recently by Cardon (8), Balfour-Paul (9), and Orna (10). The ancient andhistorical literature on dyestuffs includes the Natural History in Latin of the1st century CE Roman historian, Pliny the Elder, and the 16th century Plicthoof Gioanventura Rosetti in Italian (11). In fact, the full title of The Plictho, astranslated into English, is: “Instructions in the Art of the Dyers Which Teachesthe Dyeing of Woolen Cloths, Linens, Cottons, and Silk by the Great Art as Wellas by the Common”.

It is practically impossible to determine the geographical origin of textiledyeing. To the question of “where in the world was dyeing first performed?”one undoubtedly needs to answer that in all probability it was performed invarious locations at about the same time by using the locally available dyestuffsources. Today, we have definitive archaeological and chemical evidence thatthis craftsmanship dates back at least six millennia, and these textile dyeings arethe oldest yet found to date, and were excavated from the Cave of the Warrior inthe Judean Desert, Israel (12). In these Chalcolithic linen textiles, the dark-brown(blackish) decorative yarns were dyed with an acidic organic macromoleculedyestuff source, but whose exact nature has yet to be determined, prior to weavingthem into the textile. As for the famous purple molluskan colorant, the productionof this water-insoluble compound as a paint pigment dates from about fourmillennia ago while its conversion to a soluble textile dye probably occurredabout half a millennium later (13). Similarly, the use of the dark blue-violetindigo pigment (also known as indigotin) is from over four thousand years agoas analyzed by this author and observed from various surviving Pharaonic textilefragments in the collections of, for example, the British Museum in London andthe Metropolitan Museum of Art in New York.

The primary thrust of the current work is to portray a picture of marvel at thescientific abilities of the ancient dyer, undoubtedly achieved via empirical trial anderror experimentation, and probably with an added dose of accidental successes.He – or she – utilized vast empirical know-how to produce colorful long-lastingdyeings that have withstood the ravages of time. When the dyer used the full

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spectrum of the natural dyestuff sources available, he also applied his practicalknowledge of botany, entomology, and malacology. Further, he incorporated intohis scientific craft themethodologies generally associatedwith the following topicsin inorganic, organic, physical, and biochemistry:

• ionic, covalent, and intermolecular chemical bonding• coordinate complexation• pH control of alkalinity/acidity• enzymatic hydrolysis• photochemical chromogenic precursor oxidation• anaerobic bacterial fermentative reduction• air-oxidation

A discussion of the colorants used in ancient – and modern – times requiresa clear understanding of the difference between a “pigment” and a “dye”, whichunfortunately have sometimes been erroneously used interchangeably. Figure 1outlines the properties of these two colorants. Without any additional treatment,a natural pigment is a relatively water-insoluble colorant and is used to paint asurface. Examples are painting on a wall (as in a fresco), canvas (paintings),vessel, on a body, and even to paint on a textile (if that textile will not be washedsuch as a shroud on a coffin). In ancient times, most paint pigments were of aninorganic, mineral, nature. Conversely, a dye is a water-soluble organic colorantand that word should be specifically used when this colorant is utilized to performa true textile dyeing. Historically, some dyes were chemically transformed intopaint pigments by complexing with a metallic ion to form a “lake” used in varioushistoric paintings or in mordant dyeing – indirectly fixing the dye into the textile(discussed below). Inversely, certain pigments (such as indigo from plants andrelated compounds from mollusks) were transformed into a dye by, for example,reducing the pigment to its water-soluble counterpart, and after the dyeing this wasthen followed by air-oxidation back to the original pigment.

Figure 1. The properties of water-insoluble pigments vs. soluble dyes.

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Ancient Coordination CompoundsHistorical Mordanting with Alum

It was well known at least as far back as the Roman Period that a salt wasneeded in order to act as an intermediary and fix the dye to the textile fibers. Thisfixative is known as a “mordant” from the Latinmordere, which means “to bite” or“biting”, and it “bites” (i.e., attaches to) the dye as well as to the textile fiber. TheRoman historian Pliny clearly mentions the use of the mordant alum in dyeing,and this mineral contains the trivalent aluminum ion and is generally accepted tobe KAl(SO4)2·12H2O. The relevant passages in Pliny are from Book 35, Chapter52, as follows in Latin and in English (14, 15):

Nec minor est aut adeo dissimilis aluminis opera, quod intellegitursalsugo terrae. plura et eius genera. in Cypro candidum et nigrius,exigua coloris differentia, cum sit usus magna, quoniam inficiendis clarocolore lanis candidum liquidumque utilissimum est contraque fuscis autobscuris nigrum.

Not less important or very different is the use made of alum (aluminis), bywhich is meant a salt exudation from the earth. There are several varietiesof it. In Cyprus there is a white alum and another sort of a darker color,though the difference of color is only slight; nevertheless the use madeof them is very different, as the white and liquid kind is most useful fordyeing woolens a bright color whereas the black kind is best for dark orsomber hues.

Complexing the Dye with Alum

Alizarin and the related purpurin are the well-known di- and tri-hydroxyanthraquinone hydrolysis products extracted from various madderplants (Rubiaceae species), with the most famous being Dyer’s Madder (Rubiatinctorum), shown in Figure 2. This plant was the most widely used red dyestuffsource of the ancient Near East and also available in various European regions.

In wool, the Al3+ ion – a Lewis acid – bonds to an oxygen atom in theproteinic fiber and also to certain oxygen atoms in the dye molecule via ionic andcovalent bonds, the latter including coordinate covalent bonding. Thus, in theschematic O(wool)–Al–O(dye) bridge, the Al intermediary serves as a bridging agent– a “matchmaker” – between the fibers and the dye. However, the exact molecularstructure of this wool–alum–dye complex is still not known, and further researchinto this area would be important.

Without wool, the structures of alizarin-mordant complexes have beenstudied for bivalent and trivalent metal mordants and two of the proposed generalstructures are shown in Figure 3. In order for the C=O→M–O coordination bondto form in the hydroxyanthraquinones, the carbonyl and hydroxyl groups in theligand must be adjacent. In the structure proposed for a metal–alizarin complexin neutral media, Figure 3 (left), the hydrogen atom is replaced by the metal ion,which is followed by the ionization of the M–O bond, and the ionized hydroxyl

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group in position 1 is bonded through the intramolecular hydrogen bond (16).This complex can have more tautomeric forms that contain the six-memberedchelate cycle, and other structures have been proposed for the metal–alizarincomplex in acidic and alkaline media (16).

The metal-alizarin coordination compound in Figure 3 (right) has often beengiven (1, 17), in which coordinate covalent bonds are formed; however, the M–Obond in similar structures has been found to be partly covalent (18), so that a partialionic character can be present, and even a more fully ionized bond may exist, asmentioned above (16). Resonance structures are also possible for this 2:1 complex.

Figure 2. Left: roots of the Dyer’s Madder plant (Rubia tinctorum) with theinterior showing the presence of the red dyestuff source. Right: molecular

structures of alizarin (top) and purpurin (bottom); intramolecular H-bonds arealso present between adjacent carbonyl and hydroxyl groups in both molecules.

Further studies have also included calcium ions into the complex, Figure 4,which is a logical extension since in antiquity naturally hard water rich in calciumwas used. Further, the aluminum-calcium-alizarin complex is the dye known asTurkey Red for dyeing cotton (18). It was assumed that the groups around thecentral aluminum take on an octahedral structure (18). It is also noted that thetwo anionic oxygens are probably cis to each other in order to neutralize the Ca2+counterion on their side. If this complex would be attached to the wool thenprobably the water molecule would be replaced by the oxygen from wool.

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Figure 3. Proposed alizarin complexes with an M2+ or M3+ metal ion mordant.

Figure 4. Alizarin–aluminum complex with calcium based on the structureproposed by Kiel & Heertjes (18).

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Another elaborate structure for the alizarin–aluminum–calcium complex hasbeen given and shown in Figure 5 (19).

Figure 5. A proposed alizarin–aluminum –calcium complex. (courtesy ofMattern, R.; Wikimedia Commons).

Finally, Wunderlich and Bergerhoff (20) obtained single crystals ofaluminum calcium alizarinate and purpurinate by two-phase crystallization.X-ray structure determinations showed tetranuclear complex molecules withfour alizarins. The metal–oxygen interactions in this structure (Figure 6) aremostly coordinate covalent bonds with some ionic character. This structure isdifferent from other proposed arrangements, and the authors state that this isthe best structure. A similar complex is also given for carminic acid, whichis also a hydroxyanthraquinone, and obtained from red-producing cochinealscale insects (21).

Figure 6. The alizarin–aluminum–calcium complex based on the work ofWunderlich and Bergerhoff (20).

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With all of the differing proposed molecular structures given in the literaturefor this complex, more research in this area would be most welcome. Whatever thecorrect structure is for these mordant dyes in wool, it is remarkable that the ancientdyer was producing metal complexes and utilizing the coordination chemistryassociated with chelation several millennia before Alfred Werner (1866–1919)expounded on coordination compounds and Gilbert Newton Lewis (1875–1946)explicated his universal concepts of acid-base properties.

A beautiful example of the aluminum-alizarin complex that the ancient dyercreated is from the 2nd century CE Roman Period (Figure 7).

Figure 7. Fragments from a multicolored 2nd century CE scroll wrapper from theperiod of the Bar Kokhba revolt found in the Cave of Letters, Judean Desert; thered background was dyed with madder containing mostly alizarin and complexed

with an alum mordant.

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Redox Purple Chemistry of the Ancients

Fermentation and Vatting

As impressive as the ability of the ancient dyer to create coordinatedcomplexes is, it is the dyeing with indigoid compounds from purple-producingsea snails that really showed off the chemical prowess of this artisan. Thesepurple dyeings are famously renowned for the regalia of kings, priests, and themilitary, and referred to by various names, such as Royal Purple or Tyrian Purple.Direct archaeological evidence of dyeing with molluskan purple is based onvarious purple-stained and analyzed potsherds from dyeing vats, and dates backto at least three and a half millennia when the Levantine Phoenicians developedthis chemical technology (13).

Performing a dyeing from the purple pigment produced from certain molluskswas similar to – but much more biologically challenging – than dyeing with theindigo pigment (also referred to as indigotin). The latter colorant was producedfrom various precursors in the leaves of certain plants, such as Indigofera tinctoria(the indigo plant, so-named because it is native to India and environs), and alsofrom woad (Isatis tinctoria), a plant that was available in the ancient Near Eastand Europe (see Figure 8).

Figure 8. Left: the woad plant, Isatis tinctoria (Wikimedia commons). Right: theauthor holding a dark blue-violet indigo pigment produced from the isatans in

the leaves via fermentative reduction and air-oxidation.

Photochemical Oxidation Production of the Purple Pigment

The pigment produced from most purple-producing Mollusca is of areddish-purple coloration, an example of which is given in Figure 9. However,while a type of the Hexaplex trunculus sea snail species (also known asMurex trunculus), the most important purple-producing mollusk of the EasternMediterranean, can produce that coloration, another chromatic subgroup of H.trunculus mollusks produces bluish-purple or violet pigments. In any case,though the purple pigments from different sea snail species may contain differentcolorants, all purple-producing mollusks, whether from the waters off Japan, the

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Atlantic Ocean, or the Mediterranean Sea, possess the same common chromaticmarker, the red-purple 6,6′-dibromoindigo (abbreviated as DBI) colorant (13).

The formation of the colorants in the purple pigment from the colorlessprecursors contained in the hypobranchial gland of the living animal consistsof complex steps (22) that can be schematically outlined for the case of DBI,as shown in Figure 10. Each precursor is hydrolyzed by purpurase, a sulfataseenzyme, which is present in the gland but is not in contact with these precursorsas long as the snail is alive. When the snail expires or when the gland is cutor pierced, then the enzyme comes in contact with these precursors, whichafter hydrolysis followed by air-oxidation and photolytic processes, produce theindigoids, such as the DBI shown in the figure.

Figure 9. Left: an expiring Hexaplex trunculus sea snail expelling the colorlessprecursors from its hypobranchial gland, which under the influence of air andlight, undergo photochemical oxidation to the red-purple pigment. Right: the

molecular structures of the three indigoid components in the H. trunculus pigment(top to bottom): indigo (IND), 6-bromoindigo (also known as monobromoindigo,

MBI), and 6,6′-dibromoindigo (DBI), the latter being the most abundantcomponent of any red-purple colored pigment.

Not all snails were created equal. The major component in all red-purplemolluskan pigment from all species is DBI, and it can even be more than 90% ofthe dye content in such pigments. However, H. trunculus sea snails produce otherindigoids in varying amounts besides the red-purple DBI colorant, and these arethe violet MBI and the dark blue IND colorants. This is summarized in Figure11. The presence of a significant quantity of the violet MBI colorant is uniqueto H. trunculus snails and finding appreciable quantities of it in a purple pigment– whether archaeological or modern – indicates that its malacological dyestuffsource is from H. trunculus. In fact, MBI may even be the colorant in greatestabundance in such pigments. Further, the pigments from H. trunculus snails canbe categorized in two ways, depending on the relative quantities of DBI and INDin their pigment. Thus, one type produces a red-purple pigment because it is richerin DBI, while the other type is richer in IND and subsequently the pigment’s coloris blue-purple or violet.

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Figure 10. An outline of the spontaneous production of the DBI pigment viaenzymatic hydrolysis of a precursor in Hexaplex trunculus sea snails followed

by oxidative coupling and photochemical reactions.

Figure 11. The three Muricidae family of sea snails from which purple pigmentswere produced in antiquity (from left to right), Hexaplex trunculus, Bolinusbrandaris, and Stramonita haemastoma, and the main colorants that they

produce.

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Fermentative Bacterial Reduction

All the indigoid colorants in the purple pigment are relatively water-insolublecolorants – pigments – due to the strong intra- and inter-molecular hydrogenbonds that they form, and the solubility decreases as more Br atoms are attachedto the indigo skeleton. Thus, for any textile dyeing to be performed – whethernatural or synthetic – the colorant must be dissolved. In the case of an indigoid,this dissolution is accomplished via reduction – or “vatting” – of the pigment toyield the reduced and less-colored or “whiter” dye known as “leuco”. The naturalreducing agent to effect the solubilization of the solid pigment via fermentationis the thermophilic bacteria present in – and feeding off – the meaty glands of therotting flesh (23).

The first step in the reduction process produces the non-ionized leuco acid,which is only sparingly soluble (Figure 12). The affinity of the reduced dye to thetextile fibers will be significant when the colorant is in a soluble and ionic state, andthus the reduction is performed in an alkaline environment to produce the solublemonoanion (24). If the pH is further increased then the more soluble dianion canalso exist in appreciable amounts, but the pH should not exceed 9 when dyeing aproteinic material, such as wool, so as not to cause degradation of the textile.

Figure 12. Fermentative bacterial reduction of the indigoids to their leucospecies as a function of the alkalinity of the solution; the actual dyeing is effectedby introducing the textile in the dye vat and after a few hours removing it into theair whereby it undergoes air-oxidation to the original pigment’s components.

The fractions of the reduced brominated indigoids existing in equilibrium asa function of pH has not yet been researched, which would be of great interest,however the relevant quantities of the different species of indigo itself have been

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studied. The two equilibrium dissociation constants for reduced indigo have beenoriginally estimated from other data and reported to be 8.0 and 12.7 for pK1 andpK2, respectively (24). From an interpolation and extrapolation of the relevantcurves in recently published graphs (25), it is found that the value for pK1 isdifferent and estimated at 9.45, while pK2 is the same 12.7 value. Based on themore recent values for the dissociation constants of the reduced indigo species, thefraction of each species as a function of the pH can be evaluated from publishedequilibrium equations (25), and the classical mirror-image α-shaped curves areobtained (Figure 13). The diagram shows that at a working pH of 9, about 20% ofthe reduced indigo is in the monoanion state, whereas about 80% is the nonionizedleuco acid species. However, from the recently published graphs (25), there is asteeper rise in the monoanion composition so that its fraction is at 20% alreadyat pH 8. In any case, the monoanion species necessary to bond to the wool fibersis present under alkaline conditions. Similar results should be obtained for thereduced brominated indigo species.

Figure 13. Mirror-image α-diagram showing the reduced indigo fractions basedon the pK1 = 9.45 and pK2 = 12.7. H2I refers to the reduced (leuco) indigo acid,

HI– and I2– are the respective mono- and di-anions of reduced indigo.

The diagram shows that the dianion is indeed irrelevant at the moderatealkaline pH values that are needed so as not to destroy the proteinic wool structure.It is the monoanion that is substantive and attaches itself to the wool fibers viavarious intermolecular bonds. Hence, in effect, the relevant equilibrium is mainlybetween the reduced nonionic indigo (represented by “H2I”) and its monoanion,HI–:

Though, the mono-anion’s presence in the reduced dye vat is much less thanthe nonionic species, nevertheless as more of the monoanion is removed fromthe solution and bonds to the fibers, then the equilibrium of the conjugate acid-

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zvi

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–

zvi

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+ H+(aq).

base pair shifts to produce more of the monoanion from the nonionic acid. Thisright-shift in the equilibrium was practiced by the advanced ancient chemical dyerthousands of years before the famous French chemist, Henry Louis Le Châtelier(1850–1936), invoked his principle on the “lois des équilibres chimiques”.

Redox Dyeing

After the purple pigment was reduced and dissolved, the actual dyeing couldbe performed. The overall dyeing process then follows a reduction-oxidationcycle, which is schematically shown in Figure 14. The anaerobic bacterialreduction requires that the vat – the clay vessel containing the dye bath –be covered to minimize the entrance of air into the solution. A few days offermentation are normally required for the natural reduction of the pigment tooccur, and this can be clearly observed as the purple-color of the aqueous mixturetransforms to the green-colored solution (23). At this point, a cleaned woolenfleece is inserted into the solution and kept at a temperature of about 50 – 60°C for a few hours. Afterwards, as the green-colored wool is removed from thesolution and into the air, the reduced species in and on the fibers immediatelybegin to undergo oxidation by the atmospheric oxygen to the original purplepigment, though not exactly with the same composition as in the raw pigment.

Figure 14. Overall dyeing process including the pre-dyeing reduction stage, woolinsertion into dye bath, followed by air-oxidation of the reduced indigoids.

The essence of this dyeing strategy was in getting the pigment, whichoriginally was not connected to the textile, to impregnate the fibers, which couldhave only occurred in the dye’s dissolved state. Then, when air-oxidized to thepigment again, this pigment is now “imprisoned” inside the interior of the fibers,

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and is also attached to the external fibers, by means of various intermolecularforces. In short, the colorant is a pigment before and after the dyeing, but in themiddle stage it is in a water-soluble reduced state as a dye.

A most beautiful example of such a Royal Purple dyeing is from a minisculeweave fragment that is probably from the royal robe, cloak, or mantle of the 1stcentury BCE King Herod the Great (26), and shown in Figure 15.

Figure 15. A close-up of the miniscule fragment of only a few millimeters showingthe purple-dyed yarns from the1st century BCE Herodian fabric found atopMasada in the Judean Desert; the few beige-colored yarns are undyed woolenfibers that have yellowed and been sullied over the archaeological time frame.

Analytical Methods of Dye AnalysisAn investigation of ancient chemical technologies requires a three-pronged

approach that incorporates historical accounts regarding dyeing technologies,physical archaeological findings, and scientific analyses on these historic artifactsas well as on modern dyestuffs that would have also been in existence in antiquity.The starting point for this study is, then, a dilemma, since the relevant question is“where best to start?”. However, because the triad topics are interconnected any

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of the subjects can be approached first as one investigation leads to the others andback again to the first.

A necessary stage in the investigation is to identify the dyestuff sourcesdiscussed in the historic literature and be hopeful that they also exist in moderntimes so that these can be analyzed via advanced analytical instrumentation.Scientific analyses of these sources will produce a chemical library of the variouscolorants in each dyestuff. Towards this step, it is crucial to use the correctanalytical instrumentation for such a purpose. Unfortunately, in some cases,various instrumental techniques have been used for dye analyses without anunderstanding of these limitations. Not every instrumental technique – advancedas it may be – is automatically useful for analyses of these colorants (27). Themain limitation of all spectrometric techniques is that they produce an “overlapof data”, i.e., these techniques measure the bulk sum of all species, which canresult in an overlap of information from different components. The latter propertyis crucial to unambiguously identify the exact dyestuff species because everynatural dye source consists of several components.

Analytical instrumental chemistry is inundated with a myriad of acronymsrepresenting many advanced methods of analyses. Accordingly, the analyticalchemist is faced with such abbreviations as NDT, NDI, FORS, FAB, DESI, DART,HRMS, TOF, SERS, TERS, DRIFTS, DAD, and the list goes on. With all thesemethods, it can be confusing as to which technique to use for dye analyses, anda variety of techniques have indeed been used. In this regard, it is important todifferentiate between inorganic pigments, which are typically characterized bya metallic entity that can be relatively easily analyzed via various elementaryspectrometric techniques (such as, XRF, SEM-EDX, AA, ICP, etc.), and organicpigments and dyes.

An additional dilemma for museum officials – the “Curator’s Quandary”– is whether to use a destructive technique or a non-destructive one. ThisShakespearean predicament – “to destroy or not to destroy?” – is the question thatcurators and conservators must ask themselves. It is well acknowledged for manyyears now that the optimal method for dye analyses is HPLC (high-performanceliquid chromatography) – or its more modern “ultra” version, UPLC (also referredto as UHPLC). This technique provides the most detailed information regardingthe various dye components constituting a dyestuff or pigment. Though this is adestructive technique, it is micro-destructive – actually nano-destructive – in thatit has been shown that it can produce detailed results on even a single fiber of afew millimeters in length representing nanogram levels of dye (28). There is noother technique that can compete with LC for the full analysis of the dyestuffs andpigments. Thus, an Ecclesiastical answer to the Shakespearean question can bethat “there is a time to build, and a time to destroy”, and with the nano-destructiveLC method, producing the most detailed results far outweighs the negligibleinvasiveness of this technique (29).

An example of the detailed information produced by HPLC is thechromatogram obtained for the various colorants that may be present in amolluskan purple pigment (Figure 16). The chromatogram curve shows theseparation of each component at the time that the mobile phase elutes it out of thestationary phase – known as the retention time (R.T. or tR) – and the absorbance

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at this time. In essence, a chromatic “fingerprint” of the dyestuff is produced sothat not only a qualitative analysis is obtained of what colorants are present in thedyestuff, but also a quantitative analysis indicates how much of each colorant ispresent. Metaphorically, the human analogy is that the peaks in the chromatogramrepresent fingers and their position in the chromatogram show which fingers theyare; the heights (technically the areas under each peak) indicate the lengths ofthese fingers. For example, the red-purple and blue-purple (or violet) pigmentsproduced from H. trunculus snails can contain about 10 colorants, with yellow,orange, blue, violet and red-purple colors as shown in the figure (30).

Figure 16. HPLC-produced chromatogram of the various indigoids (IND, MBI,and DBI) and related components, with their representative colors, whichmay be present in a molluskan purple pigment. The other components are:IS = isatin, 4BIS = 4-bromoisatin (not present in a molluskan pigment but

included for standardization), 6BIS = 6-bromoisatin, INR = indirubin, 6MBIR= 6-(mono)bromoindirubin, 6′MBIR = 6′-(mono)bromoindirubin, and DBIR =6,6′-dibromoindirubin; the right absorbance scale is for the first three peaks

representing the isatinoids.

Together with the spectrometric detection of each peak, which produces aUV/Visible spectrum with the PDA (photo-diode array) detector (also abbreviatedas DAD), these two properties – chromatographic retention time and spectrometric– can be used to positively identify the colorants present when compared toa standardized library of analytical results performed on the possible naturalcolorants. An additional detector that is helpful in the dye identifications wouldbe MS (mass spectrometric).

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A normalized quantification has been made (Figure 17) on the three above-mentioned Murex sea snails that inhabit the Eastern Mediterranean – includingthe two chromatic species of the H. trunculus snails – and compared with anarchaeological pigment found on a King Darius marble jar from 2,500 years ago(31). To date, all the archaeological purple pigments that have been properlyanalyzed via HPLC have shown the significant presence of MBI. This clearlyindicates that H. trunculus snails were used in all the dyeings and paintings, aloneor sometimes together with the otherMuricidae snails, in all archaeological purplepigments found to date.

Figure 17. A multi-component normalized quantification of the integrated peakareas (measured at the standard 288 nm wavelength), which can be used assemiquantitative measures of the relative amounts of the dyes in the purple

pigments from various sea snail sources; (bottom, left to right) red-purple paintresidue on a 2,500 year old King Darius marble jar, red-purple and blue-purplepigments from modern H. trunculus, and red-purple pigments from modern B.

brandaris and S. haemastoma.

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Conclusions

The production of colorfully dyed textiles from more than four millenniaago required an advanced degree of practical chemical knowledge that was basedon inorganic, organic, and physical chemistry, and biochemistry. As such, thelong-lasting stable dyeings that we are witness to nowadays are the results ofstrong intermolecular bonds between the colorants and the textile fibers that theancient dyer created. Today, with all of the accessible modern tools, we can onlymarvel at the high degree of empirical chemistry that the ancients practiced. Intheir hoary past, with only primitive tools and primeval conditions, they exhibiteda modern mastery of chemical principles. These ancient dyers were truly Noblesof Chemistry.

Acknowledgments

The author would like to express his sincere appreciation to the Sidney andMildred Edelstein Foundation for support of this work and to Seth Rasmussen forthe invitation to deliver this paper at the American Chemical Society symposiumon ancient chemical technologies.

References

1. Koren, Z. C. Historico-Chemical Analysis of Plant Dyestuffs Used inTextiles from Ancient Israel. In Archaeological Chemistry: Organic,Inorganic and Biochemical Analysis; Orna, M. V., Ed.; ACS SymposiumSeries 625; American Chemical Society: Washington, DC, 1996; Ch. 21,pp 269–310.

2. Leggett, W. F. Ancient and Medieval Dyes; Chemical Publishing Co.:Brooklyn, NY, 1944.

3. Forbes, R. J. Studies in Ancient Technology; Vol. IV, 2nd ed., E. J. Brill:Leiden, 1964.

4. Robinson, S. A History of Dyed Textiles: Dyes, Fibres, Painted Bark, Batik,Starch-resist, Discharge, Tie-Dye, Further Sources for Research; StudioVista: London, 1969.

5. Brunello, F. The Art of Dyeing in the History of Mankind; Hickey, B., Transl.;Neri Pozza Editore: Vicenza, 1973.

6. Sandberg, G. Indigo Textiles: Technique and History; A & C Black: London,1989.

7. Sandberg, G. The Red Dyes: Cochineal, Madder andMurex Purple: AWorldTour of Textile Techniques; Matteson, E. M., Transl.; Lark Books: Asheville,NC, 1997.

8. Cardon, D. Natural Dyes: Sources, Tradition, Technology and Science;Archetype Publications: London, 2007.

9. Balfour-Paul, J. Indigo: Egyptian Mummies to Blue Jeans; British MuseumPress: London, 2011.

10. Orna, M. V. The Chemical History of Color; Springer: Heidelberg, 2013.

215

Dow

nloa

ded

by S

HE

NK

AR

CO

LG

on

Nov

embe

r 24

, 201

5 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate

(Web

): N

ovem

ber

20, 2

015

| doi

: 10.

1021

/bk-

2015

-121

1.ch

007


11. Edelstein, S. M.; Borghetty, H. C., Transls. The Plictho of GiovanventuraRosetti: Instructions in the Art of the Dyers Which Teaches the Dyeing ofWoolen Cloths, Linens, Cottons, and Silk by the Great Art as Well as by theCommon; 1st edition of 1548, M.I.T. Press: Cambridge, MA, 1969.

12. Koren, Z. C. Color Analysis of the Textiles. In The Cave of the Warrior.A Fourth Millennium Burial in the Judean Desert; Schick, T., Ed.; IAAReports, No. 5; Israel Antiquities Authority: Jerusalem, 1998; pp 100–106.

13. Koren, Z. C. New Chemical Insights into the Ancient Molluskan PurpleDyeing Process. In Archaeological Chemistry VIII; Armitage, R. A., Burton,J. H., Eds.; ACS Symposium Series 1147; American Chemical Society:Washington, DC, 2013; Ch. 3, pp 43–67.

14. Healy, J. F. Pliny the Elder on Science and Technology; Oxford UniversityPress: Oxford, 1999; p 193.

15. Rackham, H., Transl. Pliny Natural History; Vol. IX, Books 33−35; TheLoeb Classical Library, Harvard University Press: Cambridge, MA, 1961;pp 394 – 397.

16. Fain, V. Y.; Zaitsev, B. E.; Ryabov, M. A. Metal Complexes with Alizarinand Alizarin Red S: Electronic Absorption Spectra and Structure of Ligands.Russ. J. Coord. Chem. 2004, 30, 365–370.

17. Orna, M. V.; Kozlowski, A. W.; Baskinger, A.; Adams, T. CoordinationChemistry of Pigments and Dyes of Historical Interest. In CoordinationChemistry: A Century of Progress; Kauffman, G. B., Ed.; ACS SymposiumSeries 565; American Chemical Society: Washington, DC, 1994; pp165–176.

18. Kiel, E. G.; Heertjes, P. M. Metal Complexes of Alizarin I – The Structure ofthe Calcium-Aluminium Lake of Alizarin. J. Soc. Dyers Colour. 1963, 79,21–27.

19. Alizarin-Aluminium-Calciumkomplex. Wikipedia. https://de.wikipedia.org/wiki/Alizarin-Aluminium-Calciumkomplex (accessed onJuly 27, 2015).

20. Wunderlich, C.-H.; Bergerhoff, G. Konstitution und Farbe von Alizarin- undPurpurin-Farblacken. Chem. Ber. 1994, 127, 1185–1190.

21. Harris, M.; Stein, B. K.; Tyman, J. H. P.; Williams, C. M. The Structure ofthe Colourant/Pigment, CarmineDerived fromCarminic Acid. J. Chem. Res.2009, 407–409.

22. Cooksey, C. Tyrian Purple: The First Four Thousand Years. Sci. Prog. 2013,96, 171–186.

23. Koren, Z. C. The First Optimal All-Murex All-Natural Purple Dyeing in theEastern Mediterranean in a Millennium and a Half. Dyes Hist. Archaeol.2005, 20, 136–149Col. Pl. 15.1–15.5.

24. Etters, J. N. Indigo Dyeing of Cotton Denim Yarn: Correlating Theory withPractice. J. Soc. Dyers Colour. 1993, 109, 251–255.

25. Baig, G. A. Studies on Dyeing Wool with Indigo. Tekstil 2012, 61, 65–73.26. Koren, Z. C. Scientific Study Tour of Ancient Israel. In Science History: A

Traveler’s Guide; Orna, M. V., Ed.; ACS Symposium Series 1179; AmericanChemical Society: Washington, DC, 2014; Ch. 15, pp 319–351.

216

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r 24

, 201

5 | h

ttp://

pubs

.acs

.org

P

ublic

atio

n D

ate

(Web

): N

ovem

ber

20, 2

015

| doi

: 10.

1021

/bk-

2015

-121

1.ch

007


27. Koren, Z. C. Editorial: Extracting Thousands of Years of Colorful DyeHistory Through Analytical Science. Palest. Explor. Q. 2011, 143, 1–3.

28. Koren, Z. C.; Verhecken-Lammens, C. Microscopic and ChromatographicAnalyses of Molluskan Purple Yarns in a Late Roman Period Textile. e-Pres.Sci. 2013, 10, 27–34.

29. Koren, Z. C.. Non-Destructive vs. Microchemical Analyses: The Case ofDyes and Pigments. Proceedings of ART2008, 9th International Conference,Non-destructive Investigations and Microanalysis for the Diagnostics andConservation of Cultural and Environmental Heritage, Jerusalem, Israel;May 25–30, 2008; pp 37.1–37.10.

30. Koren, Z. C. Chromatographic Investigations of Purple ArchaeologicalBio-Material Pigments Used as Biblical Dyes. In Cultural Heritage andArchaeological Issues in Materials Science; Sil, J. L. R.; Trujeque, J.R.; Castro, A. V.; Pesqueira, M. E., Eds.; Materials Research SocietySymposium Proceedings, Vol. 1374, Cambridge University Press: NewYork, 2012; pp 29–48.

31. Koren, Z. C. Archaeo-Chemical Analysis of Royal Purple on a Darius I StoneJar. Michrochim. Acta 2008, 162, 381–392.

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: 10.

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/bk-

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