1. Zecchi's tubed egg tempera paints are made from pigment, freeze-dried egg yolk, gum arabic, and preservative.
- Any thoughts on freeze-dried yolk as a binder?
- What would be the reason to combine yolk and gum Arabic binders in a single paint?
2. Mysterious Craquelure. Tempera painters occasionally report a mysterious ‘craquelure’ that appears in the uppermost layers of tempera paint during the painting process. It starts out as barely visible lines that gradually increase with successive layers; as more paint is applied, lines coalesce into a network of minute cracks, and can eventually cause paint to flake and delaminate. It’s seemingly associated with well-developed areas (lots of underlying layers), and generally involves titanium white. I don’t know what causes this, I can only offer tentative explanation, among them:
a. Underbound, very diluted paint. When too much water is added, at some point the various components become so separate, binder so attenuated that the resulting paint film is friable and under bound.
b. Over saturating underlying paint layers with water. Studies of solvents applied to ET indicate that spirit-based solvents leach lipids; water seems to induce swelling in the paint film. If a curing film is compelled to repeatedly expand and shrink, the stress could weaken bonds being formed in the polymerization process, and result in cracks.
There is also the speculation that, in an over saturated surface, excess moisture might draw yolk binder downward so that upper layers become under bound and fragile. This latter theory doesn't seem as likely to me, but could it be possible?
c. Poorly dispersed titanium. TW’s fine particle size tends to clump together, and needs to be carefully and thoroughly dispersed - yet I often see students give it cursory attention with the palette knife. So, perhaps aggregate clumps of poorly dispersed titanium contribute to cracking?
I favor explanation ‘b’- because of the circumstances and solution to the mysterious craquelure I experienced a few times in my early painting days. It generally occurred when I worked very rapidly, quickly piled up layers, and thus also accumulated lots of water within the paint film down to the gesso. To fix the problem, whenever I build many layers in a short amount of time, I continually and thoroughly dry underlying layers. Since adopting these work habits, I haven’t experienced “mysterious craquelure”.
Any thoughts would be appreciated!
