Gum printing with dry pigments problems. Concentration and mixing.

Hi!

I'm trying to make gum print with dry pigment (lump black) and find it EXTREMELY difficult to get concentration and exposure right. Seems like pigment is really good at blocking UV. Is that correct what I'm seeing? And what is the correct way of mixing gum arabic with dry pigment?

Thx!
Ilya

itsskin said:

Seems like pigment is really good at blocking UV

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It is I'm not a gum printer, but if you don't get much hardening of the gum going, perhaps you're off the chart with the pigment concentration. Keep in mind that if you read other people's notes, and they use e.g. watercolors as a 'pigment', you'll have to use perhaps only 10% of the amount of pigment they're indicating. Watercolors are mostly binders, water etc, and only a small part pigment. The pigment content in watercolors varies a lot, but a good ballpark estimate is 10% at the most.

So my initial hunch is that you're probably off the charts in how much pigment you use.

Have you tried gum printing with watercolors? Using dry pigments really steps things up a notch in terms of the challenges of printing.

itsskin said:

And what is the correct way of mixing gum arabic with dry pigment?

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There are a couple of ways to do this, but so far the only way that works well for me (for carbon printing) is actually a little rock tumbler. I got the cheapest I could find and a jar of stainless steel pellets. To make a dispersion, I'll typically take something like 10g dry pigment, add maybe 20ml water to it and a few drops of Orotan 731 dispersant (many other substances will probably work, but I've had good success with the Orotan so far) and then let it roll for an hour or so. I then scoop the pellets, which are by now coated in a syrupy pigment dispersion, into a colander and catch the drippings in a measuring beaker. I rinse off the pebbles and the interior of the tumbler jar, catching the pigmented water and adding it to the beaker. I then make up the volume in the beaker to the desired amount. For 10g pigment I would aim for a 100ml volume, so a 10% w/v dispersion. This works OK so far for me. The pigment will settle after a few hours or days in this very simple dispersion, but it will distribute itself upon shaking or stirring the jar. Use the dispersion as the 'pigment' for your gum printing, carbon transfer etc.

Alternatively you could try your luck with either a paint muller or a mortar and pestle. I've had no luck with the latter - I just got lots of pigment clumping. The muller worked sort of OK for me, but the quality of the dispersion made with a tumbler is just much better. It's really hard to get a good/even dispersion with a muller and prevent any pigment clumping. It works, but it's not ideal and IMO not as easy to control as a properly made dispersion using a tumbler.
I've written a little about pigments on my blog: https://tinker.koraks.nl/photography/fairy-dust-dry-pigments-for-color-carbon/
But I still have to make an entry about the tumbler...

Again, to make things simpler, consider using a pigment that's already dispersed. Several brands retail highly concentrated pigment dispersions. You can also get them from Calvin Grier over at https://thewetprint.com/product/color-pastes/ but I generally get my pigments from Kremer: https://www.kremer-pigmente.com/en/shop/ready-made-colors/kremer-color-pastes/

Making good pigment dispersions is really a skill - or, better put: it's a pretty high-tech endeavor. It's one of those areas where a couple of firms hold very strong positions since it requires very specialized knowledge. As amateurs we can make passable dispersions that work OK-ish, but if you want something dependable, I'd really consider buying a ready-made pigment paste.

Now this is really detailed answer! Thank you! I was using 0.1g per 3ml gum + 3ml dichromate. But I skipped the grinding part.

Also don't use lump black....

nmp said:

Also don't use lump black....

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What's the problem with lovely lump?

itsskin said:

I was using 0.1g per 3ml gum + 3ml dichromate

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That sounds like a lot of pigment, but as said, I'm not a gum printer. My carbon tissue is between 1% and 3% pigment to gelatin. I could dig into Grier's gum book to see what kind of pigment loads he's using typically.

koraks said:

That sounds like a lot of pigment, but as said, I'm not a gum printer. My carbon tissue is between 1% and 3% pigment to gelatin. I could dig into Grier's gum book to see what kind of pigment loads he's using typically.

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I do carbon and was thinking about trying pigments instead of ink. Thx for the info, I'll do my experiments with 1-3% ratios too.

Ah great, then the carbon remarks will make sense to you. Perhaps based on your experience you can make sort of a 'translation' from carbon to gum in terms of pigment loads.

I've had a brief look at Grier's Gum Printing manual, but can't find a clear note on pigment load that would give you a ballpark to start out with. One thing you could do is have a look at his pigment pastes and note the number of prints he suggest can be made with a tube. Then work out how much pigment per (8x10") print that makes, which should enable you to determine how much dry pigment you need. I think Grier's pastes are around 40% dry pigment load or so.

Another, more experimental way is to just coat some gum emulsion and note how deep the black is. You only need just enough tinting strength to get the desired tone. If your emulsion is blacker than necessary, it's probably a bit high on the pigment load.