This instructable will demonstrate how to create a tri-color gum bichromate print from a digital image. Gum bichromates have a history dating to 1858, when the first color images where printed. Of course 150 years ago photographers working in large format black and white made their negatives individually using red, green and blue filters. Take note that this required panchromatic film, presumably a rare commodity in the era of orthochromatic plates - serious handicap in any attempt at full-color printing. Computers have been used to emulate that filter process for some time (remember the days before the internet, when things were printed?), so why not print those negatives using the very process that was novel before Lincoln was in the White House and remained en vogue through the early 20th century. Best to avoid waxing philosophical, but many works from the heyday of gum printing are really beautiful, inspiring images. And those works will endure the test of time, given gum bichromate's archival properties.
(Special eco-bonus: gum bichromate prints are "developed" using only water. No developer, no stop, no fixer, no toner.)
That the reader has basic skills with PhotoShop, Gimp or some other photo editing software is assumed. The purpose of this document is to explain in almost painful detail exclusively how to perform the printing portion of the process, although rudimentary information is provided, since it is vital in explaining portions of the methods used.
That the reader is skilled in working with potentially dangerous chemicals and understands the risks associated with such activities is also assumed. Warning: dichromates are poisonous and should not be ingested. Raw dichromate crystals look like orange-colored sugar but can be lethal. Be smart.
This is the starting image of carabiners used for the demonstration: the raw image with the exception of its being scaled to 1000 pixels on the long side @ 72dpi. No other changes have been made. Total eye candy.
For the camera technoids: original 3Kx2K image produced using Nikon D50 with 100mm Sigma macro @ f8 and Nikon SB-60 flash (-1 EV) with hood on Bogen 3021/3047 combination, but that's only so much nonsense.
(Yeah, yeah...so what's the deal with the process being called a bIchromate but the photoreactive chemical being used is a dichromate? At some point during its golden age, major discoveries were made in molecular chemistry, leading to a sort of unification amongst international chemistry unions regarding naming conventions. Chemically, bichromates were dead in favor of the much zippier dichromate. Photographers decided simply to ignore the chemical name change and stick with the deeply rooted bichromate. (Trivia! Get your trivia heeyuh!)
Step 1: Materials required
This process may seem material rich, which may discourage some from jumping in and giving it a try, but reasonable alternatives exist at a lower cost that will still yield stunning results.
To create color separation negatives, acquire these items:
- a computer and PhotoShop, Gimp or other photo editing software
- a digital image of reasonable resolution to create a print of desired size
- transparency film
- photo printer
To create light sensitive coating, commandeer this gear:
- liquid water color pigment in tubes
- saturated solution of dichromate (ammonium, sodium or potassium): 3 x 5ml
- 3:1 cut gum Arabic solution: 3 x 5ml
- mortar and pestle
To create final print, jack this stash:
- watercolor paper
- reasonable quality paintbrush that won't streak (quality hake brushes are quite inexpensive)
- masking tape
- print frame This does not have to be a deal breaker. A crude print frame can be made by hinging two thick sheets of glass together to sandwich the paper/negative combination. A local glass shop should be able to supply two 11x14" sheets of non-UV glass with polished edges for maybe $15 An even less expensive method that is limiting in that it permits printing with overhead lighting only is just using one pane of glass atop some flat backing. Be creative, O Pioneer.
- light source or our star, Sol
- photo trays
A work table...an Ansel Adams print of Canyon de Chelly - 26 x 20.
A 16x20 contact print print frame. This is a Bostick and Sullivan maple model. Unbeatable product.
Two sheets of *gelatin-sized* 11x14 sheets Lenox 100 paper
Color separation negatives (10" x 7" approx.)
Mortar and pestle
Gum Arabic (250ml 3:1 cut)
Ammonium dichromate (100ml of saturated sol.)
2" Hake brush
(Off camera: three 11x14" trays and a pencil that was going to make a later appearance but ended up on the cutting room floor.)