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arbrador 24-09-17 05:58 PM

Sedimentary pigments
HI All~

Watercolor painters are often discussing the charms and negatives of so-called "granulating," or "sedimentary" pigments. The terms "flocculation" or texturing pigments are also used to describe this same phenomenon. Earth pigments and others are often cited as sedimentary pigments.

We as ET artists are, of course, concerned with particle size and give a lot of thought as to whether grinding is necessary and if so how much. But I haven't seen/heard much about the aesthetics of including or excluding pigments that cause a granular texture.

Any thoughts on this topic? Obviously it's personal preference so I'm wondering what your personal preferences are. I'm tending to want a smoother surface without a distracting texture but recently thinking of including some granulation in an attempt to add some excitement to the surface.

Thanks for your ideas!

Lora Arbrador

Koo Schadler 07-10-17 01:29 AM

Hi Lora,

It’s an interesting and adventuresome idea. Before discussing granulation in egg tempera, I want to look at some terms that I think can be confusing.

From what I understand (watercolorist, please chime in) granulating is when very watered-down watercolor paint settles on the paper unevenly, creating a grainy application of paint. These irregular deposits of color are referred to as “sediments”. Hence the interchangeable terms “granulating” or “sedimentary” to describe pigments that are especially good at creating granular effects.

Flocculation – the tendency of some pigments’ particles to “flock” together - is somewhat akin to granulation (in both cases the paint appears uneven) but I believe it’s distinct in that flocculated particles aren’t settling out into sediment, but instead are clumping together.

Key to granulating is (a) lots of water and (b) using the right pigments. A pigment’s tendency to granulate is often linked to large particle size, but it’s more complicated than that. It’s true that many large pigments (5 – 50 micron), such as historic earths, granulate, but so do some modest size (1 micron) pigments. From what I understand, granulation has more to do with how a pigment does, or rather doesn't, stay evenly suspended in solution, which is influenced by not just particle size but also pigment weight, amount of water, and other factors (such as a pigment’s tendency to flocculate).

In regards to egg tempera, I’ve seen granulation occur in “petit lacs” (i.e. a puddle of very watery tempera paint applied, then the tip of the brush used to pull the paint over the area to be covered). Petit lacs are so watery they don’t leave brush marks, but because they are so watery they can leave granulation, if granulating pigments are used.

I’ve applied single layer petit lacs as a quick way to cover a lot of surface area. They can appear either granulated or quite smooth depending on the pigment and technique. I think it might be a challenge to do more than one (maybe two) layers of petit lac in egg tempera; it involves so much water that you would re-wet, disturb and/or probably lift underlying paint layers if you did too many. But I haven’t tried applying more than one petit lac layer and don’t know for sure. Maybe if you let the underlying layers cure for a while, you could get away with it.

Both granulation and flocculation are more apparent on an irregular surface because pigments catch and settle in the valleys and nooks of cold pressed watercolor paper. So the typically smooth surface of a traditional gesso panel probably yields less of a granulating effect than rough watercolor paper.

Very few pigments are large enough to result in visible texture. Some historic (prehistoric to about 1700) pigments are relatively large: i.e. 50 to 100 microns (a typical human hair is 50 microns). But the majority of pigments, even many earth colors, are only 5 to 3 microns; and modern colors can be even smaller, .01 micron. A thick application of paint can create texture, but I think it’s unlikely that pigment particles themselves do - but if you’ve experienced otherwise, let us know.

One final comment, on the term “grinding”: this involves a mortar and pestle and the literal pulverizing of material. I know you’ve actually done this, Lora (having made lapis from scratch, as you once told me). But to be clear, most pigments don’t need to be “ground”; they arrive from the manufacturers already ground to an optimal particle size (in fact, some pigments, if ground too fine, change or lose their color). I mention this distinction not to be fussy, but because I don’t want beginning tempera painters to think grinding colors is part of the job; it’s not (unless you are making lapis from scratch). What tempera artists do is disperse or mill pigments; i.e. use either a muller or palette knife to combine pigments with water and egg. Neither a muller nor palette knife is strong enough to “grind” a pigment and affect its particle size.

Have you tried granulating yet in ET? Please let us know if you do. It's always great to have a new topic on the forum.


arbrador 16-10-17 04:21 AM

Hi Koo~

Thanks for your, as usual, in depth and in detailed explanation. It really helps to get the terms and science right.

Beyond petit lac, I have been using both "pulling" and "pouring techniques", both watercolor techniques. But I do them in egg tempera on gesso. I literally let the dilute paint drip off the edges as it will. I believe it does lift the gesso but then the gesso settles back down.

I have seen some fine cracking, though, in certain areas so I would not recommend this technique although, as in a previous recent post about cracking, I'm not sure that these very fine cracks (ie cracquelure) will affect the life of the painting. It seems to happen in areas where the paint tended to pool rather than run off the edges.

Anyway back to the topic of granulation, If I pour dilute paint but am careful not to let it pool, I do get quite a bit of granulation with certain pigments. It does create a lively effect that I'm experimenting with.

I agree though, with Koo's explanation, that the phenomenon happens when there is lots of water and pigments that tend to granulate.

One comment that I may beg to disagree with is about grinding with a muller. When I used to make green paint from malachite jewelry, I first smashed it in my brass mortar and pestle as fine as I could. I would then grind it directly into egg yolk on a slab of glass that i had ground carborundum grit into to rough it up.

I could literally feel the gritty pigment particles smooth out under my muller so I do think this was more than dispersion but maybe I am missing something here. BTW, for those out there who have not tried it, making malachite pigment from thrift store malachite jewelry is quite easy and exciting although I now use artificial malachite pigment which looks pretty much the same.


Koo Schadler 17-10-17 04:00 PM

Hi Lora,

Thanks for the clarification regarding "grinding" with a muller; i.e. that you've successfully smoothed pigment particles using a roughened slab and muller. You have a lot more experience in that regard than I have. I imagine it is very exciting to make pigment from old jewelry!

Still, it's important to distinguish between grinding/pulverizing versus dispersing/milling, and that the vast majority of commercially purchased pigments do not need grinding beyond what the manufacturer already has done - although, to your point, if a painter buys an earth pigment that feels too gritty, it's good to know that a muller and slab is sufficient to smooth the rough edges.

All oil and egg tempera paintings eventually develop, with age, a fine craquleure pattern - a result of polymers in the paint film shrinking and losing elasticity, and of stresses in the support. So fine cracks are inevitable (given enough time) - but not desirable, as they invite humidity into the paint film and are the beginning stages of potential delamination. If a painter is interested in longevity in a painting, cracks are definitely to be avoided in the short term (when a painting is first made) and, to the extent possible, delayed in the long term (by making strong paint films, not subjecting a painting to solvents that can leech out fats and decrease elasticity, placing a painting on a stable support, etc).

Why you're getting cracking in pooled paint, I'm not sure. A guess is that the paint is too thick there, and/or the components of the paint have separated out and there too much or too little yolk in those areas. Not the end of the world...then again, not ideal either.


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