Gumprint e

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GUM PRINTING

René SmetsJanuary 2015



GUM PRINTING This description is focusing on the practical gum printing aspects; the history of thetechnology and other theoretical developments , which can e found easily on Google, willtherefore not e dealt with !

1. The paper The most appropriate ones are the thic"er, #$$ % rag, acid&free papers such as a!o! 'rches or(ahnem)hle, weighing *$$ gsm +gr s-!meter. or more! /ollowing papers have proved to ee0cellent for the process1 /a riano 23, /a riano 'rtistico, 4anson Montval, 5/6 Rives,7hatman 7atercolour, 'rches Platine, (ahnem)hle etching paper!

8uring the process, the paper is soa"ed driedseveral times, and this usually causes someshrin"age! The negative needing to e printedprecisely in the intended position, it is essential toevaluate accurately this shrin"age! 's the paperalso has the tendency to shrin" more in onedirection than in the other, we therefore have todetermine first the shrin"age direction of thepaper!

(ere is how1

8raw two arrows in the same direction on thesheet +see s"etch 9#a.!

Now cut two e-ual straps paper, one along thedirection of the arrow, a second in the otherdirection + see s"etch 9#a.!

7e moisten the front side of thesestraps and let them dry on a flatsurface! 'fter a while, we see that

the straps curve in one direction!+see picture P:.!

This indicates the fi er orientationof the paper which gives the mostshrin"age!Using the arrows, we can now cut from our large sheet of paper thepieces that we need, ma"ing surethat the shrin"age direction followstheir short side! +see s"etch # .!

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4. Arabic gum

This is also supplied under various forms, from chun"s to fine powder! + see picture PB.!

If you want to get good -uality, it is est to ta"e chun"s that you will rea" and grind y yourself!

The gum is done in a pouch which is suspendedin water, as one would do with a tea ag!

Recipe1

– 'ra ic gum B$ gram – distilled 8M water #$$ ml

'fter a few days the gum is dissolved in thewater; after filtering it is immediately usa le!

This solution will "eep for a short time only! Its shelf life can e significantly e0tended yadding one of the following preparations to # liter of gum solution1 & #$ drops of a :% methyl para en solution = or1 & #$ drops of a $!:3% sodium en<oate solution = or1 & # to 3ml of a #$% thymol solution +#gr thymol in #$ ml isopropyl alchohol!. = or1 & 3ml of a #$% salicylic acid solution

I am using 3 ml of a #$ % mercury chloride wor"ing solution!N>TE1 Mercury chloride is to0ic, and not advised for those who are not familiar with the

manipulation of dangerous chemicals!!!5. The light-sensitive emulsion.

The gum is sensiti<ed with potassium dichromate! It causes the gum to harden when e0posed tolight! The peculiarity of this chemical is that the more of it you use, the more the image ecomescontrasty, while it also increases the light&sensitivity of the emulsion! That property is -uiteconvenient for us, when we have to uild up the contrast in our image!

Recipe1 – Potassium dichromate #$ gram – 8istilled 8M water #$$ ml – 'mmonia : ml

This solution has a long shelf life when stored in a rown ottle! 9ome sludge might settle onthe ottom of the ottle, as #$% is a saturated solution!

. The gum mi!ture.

' gum print can e made in almost any color! In the case of multiple print runs, one can eitherstic" with the same color, or use a different color for each print run!7atercolor pigments in tu es can e used, as well as pigment powders, grounded and mi0ed

y yourself with the gum!5est is to start mi0ing the gum with the pigment, adding the orange potassium onlyafterwards; in doing so one has a etter control over the color he wants to use!

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7ith gum printing, it is almost impossi le to get ma0imum lac", as well as all possi leintermediate shades of gray, in a single pass! >ne has to uild up the contrast! This is done yprinting different precisely superposed layers, each with different amounts of potassium,pigment and an appropriate e0posure time! >ne could print three layers for e0ample1 oneeach for the light, the dar" and the middle tones of the picture!

". #!posure.

This can e done in daylight, ut the maFor draw ac" is that this light can e -uite changing =a varia le that doesnDt simplify the calculation of the correct e0posure time!!! Thereforewor"ing with U? artificial light might e preferred! 9everal trial e0posures will lead to thecorrect e0posure time, allowing for a reproduction of the highlights as pure white!In our case, we got a 3 minutes e0posure using a Philips facial tanner!+Note1 7ith multiple layer printing,the negative has to e precisely positioned for each pass1thatDs what printing registration is a out! More on this in 'ppendi0 *, page @.!

$. Processing.

Processing a gum print actually means washing away the gum that wasnDt cured y light!'fter e0posing, the paper is slid image down into a water ath and -uietly let there for atleast *$ minutes; the development can then e accelerated with a simple plant sprayerproFecting a fine mist on the parts to e cleared, or the print can e left in the water until nopigments are coming off any more +this usually provides the finest detail; a forced wash might

e too rough and eliminate some delicate tones.

/irst layer for light tones1

Prepare the following mi0ture1 – ml! gum – ml potassium dichromate – $!H3 gram pigment – : drops 'gepon +wetting agent.

E0posure time is a out 3 minutes!

+9ee picture P a.!

Using a pencil, mar" the position of the image corners on the paper!4oat this surface with a soft nylon rush, a (a"e rush wor"s well also! Use only a small-uantity of mi0ture and spread it with rush stro"es in cross directions; continue until thelayer ecomes as even as possi le! ' wetting agent such as 'gepon helps to get a etterspread!/inally, the layer has to e evened with a thic" adger rush; this is done y wagging soft,short rush stro"es over the layer until one sees that the pigment is evenly distri uted on thepaper!

eave the paper lying flat for a few minutes, allowing the layer to stiffen somewhat eforehanging the paper to dry! The drying time is a out half an hour at room temperature!

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Picture P shows what the image should e loo"ing li"e after the first layer!

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9econd layer for the middle tones1

Prepare the following mi0ture1

– ml! gum –

ml! potassium dichromate – $!@ gram pigment – : drops 'gepon +wetting agent.

E0posure time is a out Bmin *$ sec!

+9ee pictures PHa J PH .!

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Third layer for the shadows1

Prepare the following mi0ture1

– ml! gum –

#$ ml! potassium dichromate – # gram pigment – : drops 'gepon +wetting agent.

E0posure time is a out B minutes!

+9ee pictures P a J P .!

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Normally our print will show now a full tonal range, from white to lac" and all theintermediate shades!The orange potassium might cause a slight yellowish stain in the paper! This can e removedwith a 3% potassium meta isulfite solution! In this ath the color should -uic"ly disappear!Thereafter, the gum print is thoroughly rinsed and dried! Please note that the layer, whichconstitutes a real relief on the paper, is very fragile while it is wet!

APP#%&'(.

1-Pro)ucts

This picture shows various products that can eused to harden the gelatin + formaline andchrome alum., and to "eep the gum solution+mercury chloride.!

2- *+ personal proce)ure

The pictures elow illustrate my wor"ingprocedure1 the products used for the emulsionon picture P@ +from top to ottom, J from leftto right1 mercury chloride, potassiumdichromate, 'gepon, ivory lac" J 6assel earthpigments., as well as a few accessories foreasier pigment manipulation!

The measuring oards havedifferent holes correspon& ding to various amounts ofpowder pigment in grams1 I fill one of the holes withpowder pigment, turn the

ottom away, and thepowder falls in the gum!

The lower tool is used forpigments in tu es1 afteradapting the pigment tu eon the fle0i le cylinder, Islide the pin with the reddot onto the tag on thecylinder indicating thedesired amount of pigment!I then pinch the pigmenttu e until the pigmentreaches the pin +this is

visi le, as the cylinder ismade of transparent plastic.! 7hen the piston is moved forward, the pigment falls in the gum solution!

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(ere is the dish I use to mi0the pigment with the gumsolution !

It consists of a frosted glassplate and, glued on top of it,a solid surface, non&porouspanel with a circular cutout!

I use a glass muller for thegum pigment mi0ing !

The first gum layer was appliedon the paper; it now has to eevened with a adger rush!

3- ,egistration printing

' good gum printusually has aminimum of threesuperposed layers,each with a specificgum, potassium, pig& ment and e0posuretime com ination!Positioning our nega& tive e0actly in thesame position andalignment for each

layer is of utmost importance! This is called registration printing!

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This can e achieved when pric"ing four holes through the negative and the paper in thecorners of the image with a needle; using the same needles at every e0posure ensures thatthese holes perfectly overlie each other! ' much safer alternative is to wor" with a hole punchand registration pins mounted in the contact print frame! +see picture P#:.!

4- Pigment tests

9ince we wor" with colour pigments on white paper, chances are that the paper sometimes wille permanently stained y the pigment! To avoid this, it is advised to si<e the paper!

5ut even so, somepigments can leave apermanent stain, whichprevents us from gettingreal white in our image!

>n the right, a test that

IDve done with variouscolour pigments1

& ?arious proportions ofgum and pigment aresimply mi0ed together , asshown in the top line! & >nce the gum is dry, thepaper is soa"ed in water!The gum dissolves, leavingor not a pigment stain! It iseasy to see for each colorhow much pigment wasmi0ed, and what limitsshouldnDt e passed toavoid staining!

's you see, some pigmentswill stain the paper,whatever the -uantityused! These pigments arenot ade-uate for our use!

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5- verprinting

It is almost impossi le to get pure white,ma0imum lac", as well as a road range ofgray shades from a single pass in gum printing!This appears clearly when reproducing a stepwedge, as shown here!

This means that we have to uild the contrastwith multiple layers!

7e have thus to print several layers inregistration on each other, each with differentamounts of potassium, pigment and a specifice0posure time

>n the right three separate layers are shown

separately1 one for the light tones, one for the shadowsand one for the middle values of the image!

7hen printing them e0actly over each other,instead of separately, one can achieve analmost full tonal scale!

RENK 9MET9 Lanuary :$#3

+translation dutch&english1 Lac-ues 6evers.

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4>NTENT9

#! The paper p! #

:! Pre&shrin"ing the paper p! :

*! 9i<ing the paper p! :

B! 'ra ic gum p! *

3! The light&sensitive emulsion p! * ! The gum mi0ture p! *

H! E0posure p! B

! Processing p! B

'ppendi0 p!

+#. Products p!

+:. My personal procedure p!

+*. Registration printing p! @

+B. Pigment tests p!#$

+3. >verprinting p!##

Picto 5enelu0 is an informal group, open to every ody in the 5enelu0 who has an active interest in anyphotographic processes developed from the very eginning of Photography! The aim is to revisit them,while respecting anyoneDs creative approach!

http1 www!picto!info 4ontact1 Lac-ues 6evers & Fac-ues "evers!org

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