Gum Bichromate Printing

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Rangefinder Filipinas Alternative Processes Workshop N 1


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Resource Person: DingPanganiban

Ding Panganiban is aFilipino Fine-Artphotographer basedin

Paris, France.

On March 16, 2013,Mr Panganibanconducted an

Alternative-Processworkshop withRangefinderFilipinas.


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Gum bichromate, or gum dichromate as it is also known, is a photographic printing process

invented in the early days of photography when, in 1839, Mungo Ponton discovered thatdichromates are light sensitive. William Henry Fox Talbot later found that colloids suchas gelatin and gum arabic became insoluble in water after exposure to light. AlphonsePoitevin added carbon pigment to the colloids in 1855, creating the first carbon print. In1858, John Pouncy used colored pigment with gum arabic to create the first color images.

Gum prints tend to be multi-layered images sometimes combined with other alternativeprocess printing methods such as cyanotype and platinotype. A heavy weight cottonwatercolor or printmaking paper that can withstand repeated and extended soakings is best.Each layer of pigment is individually coated, registered, exposed and washed. Separationnegatives of cyan, magenta, and yellow or red, green, and blue are used for a full-colorimage. Some photographers prefer substituting the cyan emulsion in the CMYK separationswith a cyanotype layer. A simple duotone separation combining orange watercolor pigmentand a cyanotype can yield surprisingly beautiful results.

Low density photographic negatives of the same size as the final image are used for exposing theprint. No enlarger is used, but instead, a contact printing frame or vacuum exposure frame is

used with an ultraviolet light source such as a mercury vapor lamp, a commonfluorescent black light, or the sun. The negative is sandwiched between the prepared paperand a sheet of glass in registration with previous passes.

The print is then floated face down in a bath of room-temperature water to allow the solublegum, excess dichromate, and pigment to wash away. Several changes of water bath arenecessary to clear the print. Afterwards, the print is hung to dry. When all layers are completeand dry, a clearing bath of sodium metabisulfite is used to extract any remaining dichromateso the print will be archival.

-wikipedia http://en.wikipedia.org/wiki/Gum_bichromate
http://en.wikipedia.org/wiki/Gum_bichromatehttp://en.wikipedia.org/wiki/Gum_bichromate


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The Workshop

Introduction tothe process, andhistory.

An overview ofthe method.

Safety and Hazard

Concerns.


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The Workshop

The Tools and Materials:

1. Chemicals: Gum

Arabic, Sodium

Bichromate, Pigment

(watercolour base).2. Tools Flat brushes,

Mixing Vessels,

Measuring Cups,

Mixing Sticks,

Individual Containers

for Participants.

3. Watercolour paper,medium to heavy

weights.

4. Printing Frame.

5. Exposing Source

(Bright Sunlight or

Artificial Light Sourcewith strong UV).


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The Workshop

The Type of Print, aswell as the Huespossible are discussed.

The importance of thechoice of paper type isstressed.

The Ideal Print Qualityis demonstrated based

on finished examples.


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The Workshop

Like any chemical basedprocessed, the final Print ismade from a Negative.The negative can be anoriginal camera negative.Or it can be a copy negative

created digitally fromanother smaller negative, adigital capture, or even anexisting photograph.The printing negative mustbe the same size as theoutput print since the printis produced using the

Contact Printing method.Ideally the printing pnegative is made on atransparent acetate base,but one made on paper canbe used as well. The PaperNegative is treated withwax and heat to make it

more translucent.


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The Workshop

The Finished Waxed-

paper Negative, ready to

be used for Printing.

The negative used for

Alternative PrintingProcesses is usually high

in contrast.

This negative can also be

used for other Alternative

Processes like Salt

Printing, AlbumenPrinting, etc.

Paper was the base for

negatives in some 19th

century Photography

media like the Calotype,

and the early Kodak rolls.


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The Workshop

Preparing the ChemicalCoating

Pigment is added to the GumArabic solution.

Gum Arabic is colourless. Thecolour of the pigment willdetermine the hue of theprint.

Pigment is added sparingly,just enough to colour the gumsolution significantly.

Some Bichromate is thenadded to the pigmented gumsolution. The Bichromatemakes the gum solution light-sensitive. The reactions whicharise from photosensitivitycreate the imprint on thepaper.


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The Workshop

Mr Panganiban demonstratesthe proper application of thesensitive coating on paper.

The brush strokes, as well asthe amount of the sensitised

gum, are very critical.

The sensitised compound hasvery low sensitivity. Itspreparation and the coatingon paper can be done in brightroom light. The compoundwill only react to brightsunlight or a light source withrich Ultraviolet output.

After coating, the paper is setaside to dry.


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The Workshop

The Brush strokes, like inPainting, are critical to thequality of the final print.

The strokes must be even andfeathering must be avoided in

the picture areas.

Strokes which leave thinner orthicker coatings must beavoided since these makeuneven coatings which willcause uneven densities in thefinal print.

The coated area, ideally, mustbe slightly bigger than the

negatives picture area.


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The Workshop

The Participantscoat their ownpaper.

Contact with thesensitised Gumsolution orcontamination withother chemicals

must be avoided.Contamination canruin the resultingprint.


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The Workshop

Once the coatingdries, the negativesare prepared forprinting.

The negatives arelaid next to thesensitised papers onwhich these would

be printed on.

The coating ischecked for eveness.


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The Workshop

The Negative and thePaper are sandwichedtogether in a printingframe.

The printing framebinds the negative andpaper intimately.

Less than perfectcontact is notdesirable- this will lead

to unsharp details.

The printing frame isthen laid under theExposing Light Source.


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The Workshop

Bright Sunlight is normallyused.

In the Workshop, artificialsunlight was used. Thissource approximated the

effect of bright sunlight atnoon.

A test exposure is madefirst.Gum Bichromate is mostdifficult in this regard since

unlike the other processes,no reaction is immediatelyseen- the coating does notshow any physical change.In other processes likeCyanotype or Albumenprinting, the image is seento come out, slowlydarkening during exposure.


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The Workshop

Placing the printingframe closer to thelight source willshorten the ExposureTime.

After testing, it wasdetermined that theexposure time was 3-5minutes.


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The Workshop

After the 3-5 minuteexposure time, theprinting frame isremoved from the

exposing lightsource.

There is noperceptible change

on the paper itself.


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The Workshop

The paper is removed

from the printing frame.

It will appear as it had

before exposure.

In Gum Bichromateprinting, light exposure

causes the bichromated

pigmented gum to harden

and become insoluble in

water. The areas shielded

by the density parts of the

negative will remainsoluble, and those

exposed by the clear parts

of the negative will

harden.


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The Workshop

The unhardened partsslowly dissolve inwater, leaving onlyhardened, pigmentedparts.

The cleared parts willlet the paper baseshow through, and thehardened pigmente dportions are the imageareas.


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The Workshop

After a few moreminutes, the Imagebecomes more visible.


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The Workshop

Sometimes theexposed gum layerneeds to be scrubbedto make the imagecome out faster.

Normally, the gumlayer is quite fragileand lifts off easily if thewater is too warm orthrough physicalcontact.

But sometimes,thegum layer is gets toohard for normal lifting

through soaking.


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The Workshop

Spraying the exposegum layer canhasten the liftingprocess and increase

the image contrast abit.


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The Workshop

Local details can betouched up bybrushing off gumareas which do not

lift off entirely.


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The Workshop

The

Washed

Print.


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The Workshop

The

Washed

Print.


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The Workshop

The

Washed

Print.The wet

print is air-

driedslowly.


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The Workshop

The wet

print is air-

driedslowly.


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The Workshop

The Dried Prints are quite

Stable, if the washing is

thorough and no

chemicals are retained by

the paper.

The Picture is as

permanent as the

pigment used.

Unlike most photographic

processes, the Gum print

is relatively stable andpermanent. Pigments last

a very long time, unlike

the inks or dyes used in

conventional or current

printing methods.


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c. 2013. Rangefinder Filipinas & Jay Javier

Gum Bichromate Printing

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