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
- pins
- 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

What's pictured:

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.)
Masking tape
Measuring droppers
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.)
This is a really fabulous instructable and your results are amazing. Great work! <br> <br>I do wonder, however, whether it's wise to wash dichromate, and indeed cadmium yellow, down the sink.
<p>Dichromates are poisonous, so it's definitely not a nice thing to add flush down the drain, but it's so diluted by the time it's rinsing off the print, I would think it isn't a huge deal. Perhaps more important to note is that potassium dichromate is an oxidizer (will add fuel to a fire), so you definitely should not throw it in the waste basket. Washing it down the sink with water is the safest thing for your home/studio. </p>
The amount of pigment is ridiculously small. Think of the millions of watercolorists out there using cadmium yellow and washing their brushes in the sink. We should probably concentrate our cadmium concerns on batteries. <br> <br>The dichromate I ride the fence on. Recovering the water from the first wash, which should be a gallon or two, for recycling would eliminate the vast majority of the dichromate from going down the drain. On the other hand, storing six gallons of water per print (and I usually work three at a time...18 gallons total) until I can take it somewhere, where it'll be treated by even more harsh chemicals...you get the idea. <br> <br>Thanks for your kind words.
<p>This instructable is really great, a lot less intimidating for a beginner than the article on gum printing on the website about alternative photography we all know (If you don't, you can spend ~10sec searching to find it). When I finally get around to try this, I don't think I will do tri-color right away, monochrome will be just okay (And I like monochromes).<br><br>I don't know, whether You are still active or not, but if You could make a similarly informative and easy-to-follow instructable on paper sizing, I would be thankful.</p>
Brilliant! <br> <br>Thank you SO MUCH for sharing this process. Your instructions are clear and well written, and the process its self is fascinating. <br> <br>I have even MORE respect for those early photographers, (Imagine lugging an old plate camera around Yosemite), where things could go TERMINALLY wrong at any of a dozen and one different points allong the road from taking a picture to hanging a finished print. Even understanding the chemistry only helps you SO FAR. <br> <br>I'm dying to give this a go some time. <br> <br>Might have to build a camera first... <br>
Great Instructable!!
It's just a wonderfull work, really really nice work. I love it. It reminds me the polaroid pictures. <br>The proces is a little bit similar to the three color screen print. <br>Probably i can't do it, but is a nice work, i will give it a try someday. <br>

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