How to work with some pigments?

[Lightfire]

Hello everyone,

I've ordered some dry pigments powders for gum bichromate and carbon transfer printing, but I've faced some problems with pigments such as graphite or metallic ones, because it seems to impossible to turn them into a homogeneous paint/pigment paste. It only creates some kind of uneven grain. How to solve this problem?

Thank you in advance!

 

[koraks]

If by metallic ones, you mean things like iron oxide - they're difficult to work with. Especially iron oxide, as it's actually influenced by magnetic fields (including the magnetic field of the earth!) which makes it hard to keep it evenly distributed.

Furthermore, some pigments aren't ground fine enough to make a decent dispersion. I've had this with iron oxide but also with carbon black pigments. You want the pigments to be really, really finely milled to begin with. I suppose it's theoretically possible to grind your own pigments, but I wouldn't know how to as I've never looked into it. It also sounds like a major challenge to me to grind pigments at home to obtain an even and very fine particle distribution.

The uneven grain description could also related to a phenomenon called 'pigment clumping', which is basically agglomerates of pigment sticking together. This happens if your dispersion technique or materials aren't appropriate, and it apparently also can happen if you add a cold pigment dispersion to a warm gelatin glop (although I haven't had this problem).

To get a decent dispersion, I've personally tried a paint muller, a mortar and pestle and a simple ball mill. The muller works and gives a decent dispersion, but along the edges of the mix, there tend to be some clumps that I could never get rid off, so it wasn't perfect. The ball mill works very nicely, wasn't very expensive (<€100 including a jar of stainless steel pellets), but only works for me for dispersions up to a content of, say, 10% or so. Which, btw, is ample for my purposes. I've had absolutely no luck at all with a mortar and pestle and quickly gave up on it. There was no way to get a decent dispersion this way.

Personally I use Orotan 731 to make my dispersions. I'm not sure if this is the best match for my application, but it appears to work very well. It only takes a drop or two to disperse several grams of pigment. I've not (yet) tried classical methods employing e.g. savon de Marseille, but these might/should work as well.

Hope this helps. Out of curiosity: how are you dispersing your pigments currently, and what materials do you use?

 

[Lightfire]

If by metallic ones, you mean things like iron oxide - they're difficult to work with. Especially iron oxide, as it's actually influenced by magnetic fields (including the magnetic field of the earth!) which makes it hard to keep it evenly distributed.

By metallic ones I mean the ones based on mica, actually

how are you dispersing your pigments currently, and what materials do you use?

I tried using both muller and a mortar with a pestle, both worked fine enough with the pigments I use mostly. Muller works better of course.

I used dry pigments such as ultramarine, yellow ochre and so on, but got an interest in making a glop with some kind of metallic pigment.

 

[koraks]

Gotcha, so by metallic, you don't mean their chemical composition, but the 'metallic' glitter effect.

I've never used a mica-based pigment, but I can imagine that the nature of the material is problematic. Mica, AFAIK, tends to form flakes more so than cubic or round particles, and I suspect it needs to be rather coarse in order for the metallic sparkle to work well. As such, it seems to me it's prone to major dispersion problems.