[Alt-photo] Gum pigment mixed in batches

Christina Z. Anderson christinazanderson at gmail.com
Tue Jan 9 15:18:14 UTC 2018


What everyone has said is good but I’ll add one thing. 

When I came across a mention back in the day (1800s) of a practice of mixing the gum/pigment/dichromate up 48 hours before use to “ripen” it, it got me wondering. 

So I took some gum and dichromate and mixed it up and left it in the dark for five days and then one cup put in the sun and then the dark for the same period of time to see both light and dark reaction (no pigment so it wouldn’t be influenced by color). Sure enough, it slowly darkens and the gum/dichromate that was left outside for a bit got dark gooey lumps in it and looked like molasses. The one left in the dark only got to a dark orange color. 

However, it did not, surprisingly, harden solid all the way through, but was a sort of syrupy liquid. 

Then I exposed both of those solutions on paper and they both exposed and hardened as expected, but the one from outside resulted in a dark lumpy layer. 

Not best practice, of course!

But what it did teach me was that when I do workshops where we are gum printing the whole week, I mix up a batch of dichromated colors (magenta, blue, yellow) and we use them until they are used up. Perhaps 1/4 cup of each color, enough for 12 or more 8x10s. They last fine and work well for 24-36 hours. Maybe even 48 but I have not tested them longer because they are usually used up by then. And this is in regular room light. I’ve done this for quite a while now so it is “time tested.” And at home I’ll do the same with smaller batches, i.e. I do not toss the extra gum/pigment/dichromate until the end of the printing session.

I do keep all gum and colors premixed in 250 ml plastic bottles so at time of use I only have to squirt the colored gum into a cup and add dichromate. SO much easier and no lumps of color that streak your paper.


Christina Z. Anderson
Contemporary Practices in Alternative Process Photography series <https://www.routledge.com/Contemporary-Practices-in-Alternative-Process-Photography/book-series/CPAPP>

> On Jan 8, 2018, at 9:44 PM, Francesco Fragomeni via Alt-photo-process-list <alt-photo-process-list at lists.altphotolist.org> wrote:
> Hi all,
> Quick question. I'm sure this has been asked but I can't find it. Can gum
> bichromate pigment be premixed in larger batches rather than being mixed at
> coating time? I'd like to mix stock pigment solutions and keep them stored
> in glass bottles that I can reach for across printing sessions (rather than
> mixing fresh for each print). Is there any reason not to do this? I think
> I've heard of people doing this but wanted to double check. Thanks!
> -Francesco
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