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Moderator Answer
(koo schadler)
Hi Eli,
I do not have the problem you are describing with small particle size pigments, for several reasons - which may (or may not) be helpful to you.
1. I limit the number of small particle size pigments on my palette. I understand - there's really no substitute for the chromatic intensity of Pthalo colors. But is there a reason to use carbon black? Maybe for you, there is; however to my eye Mars black is a gorgeous black, and a million times easier to work with than a carbon black. So perhaps you can swap out some of your smaller particle size colors with a larger particle size without compromising your aesthetic.
2. When I use very small particle size colors, I always use a commercial dispersion. My quinacridones (I have several types), Prussian (one of my favorite colors), pthalos (I have two, used to paint favorite satin cloths) and benzimidazolone yellow are all commercial dispersions from Guerra Paint, NYC. Guerra has one of the largest selections of dispersions in the USA, including many high chroma, modern colors (as well as carbon blacks in dispersion). I also buy dispersions from Natural Pigments and, in the past, Kremer. Buying small particle size colors as commercial dispersions costs a bit more but saves time, messiness, and assures a much better dispersion of pigment particles.
3. When making paint using small particle size colors, I take more time and energy to disperse the color into its binder. Because I mix small amounts of paint (generally 1/4 to 1/2 teaspoon), good dispersion, for me, means keeping my palette knife parallel to the glass palette, and applying more time and elbow grease (a paint technician at GOLDEN's told me that keeping the knife parallel and working hard creates as much "sheer force" as a mechanical paint mill, and thus is sufficient when mixing small quantities of paint). For larger amounts of paint (which is likely how you work, given your larger surfaces) it's important to use a muller instead of a palette knife; still, as with a palette knife, for small particle size color you need to spend extra time dispersing, and really work it, put muscle and energy into the process.
4. Sealing a paint layer, when necessary, with a glaze or nourishing layer. You mentioned you've tried this approach - it's a good one. However the difference in our approaches is that I would not change my tempering in the glaze layer. I try to temper every paint correctly, regardless of the pigment, regardless of what layer it's in a painting.* So, if my small size pigments, properly tempered, feel like they may travel and I want to "seal" them off, I'll apply 1 to 3 layers of larger sized particle pigment (easier to disperse) on top, also properly tempered, not with extra egg. A single, well-tempered layer of very thin (glaze or scumble) paint applied on top is generally enough to "seal off" a potentially problematic underlayer. Or, if you don't want to apply a new color on top, you could "seal off" the problematic layer by applying a thin nourishing layer of pure egg yolk and water (about 1 part egg to 8 parts water).
(*...the exception being if the underlying paint layer is notably undertempered; in which case I would add a bit more egg to the layer on top, to help "nourish" the undertempered, underlayer of paint - but I wouldn't add a lot of extra egg, just a little.)
In my teaching experience I've had dozens of students build up a background of Prussian blue and, because they are new to particle size, dispersing, etc., the students have not fully dispersed the Prussian (even tho' I give a commercial dispersion in the classroom - they just haven't given enough time and elbow grease when they're making paint) - and they're getting streaks of Prussian or it's traveling onto their hand, etc. I explain how they need to spend more time dispersing small particle size colors; then I apply a single glaze or nourishing layer on top and, voila, the problem is solved. So truly, I know the challenge of these small particle size colors - but there is a way to work effectively with them, and it shouldn't involve having to change your tempering.
I hope that helps. So glad we have someone interested in talking egg tempera! Always good to hear from you, Eli.
Koo
