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Old 01-01-18, 03:17 PM
Koo Schadler's Avatar
Koo Schadler Koo Schadler is offline
Tempera Painter
 
Join Date: Dec 2003
Location: Alstead, NH & Zirahuen, Mexico
Posts: 317
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Hi Rebecca,

Pure egg tempera paint and egg oil emulsions (which have more egg than oil and are water soluble) dry to the touch very quickly (within seconds for thin applications of paint). This initial drying is merely the evaporation of water content from the paint.

The second step in “drying” is polymerization: the process of proteins in the yolk and/or oil linking up (think of a bowl of spaghetti – protein strands – curling around one another) to form polymer chains. Polymerization occurs gradually, through the absorption of oxygen. UV light (from sunlight and some artificial sources) expedites polymerization in egg yolk. For egg tempera it takes about 3 to 6 months for complete polymerization (depends on # of layers, thickness, drying conditions); oil paint needs anywhere from 6 months to many years (for very impasto paint) to fully polymerize.

(An aside: Heat also speeds up polymerization of yolk – think of what happens when you cook an egg – but too much heat is not good for either the yolk or traditional gesso, as it can create cracking and makes minimally less translucent paint films).

Once egg tempera and egg oil emulsion paints have fully polymerized, they are no longer water-soluble. So the longer you let your painting sit, the further along it is in polymerization, the less likely underlying layers are to lift when fresh paint is applied.

You can wait 24 hours, or 48 hours, or a week...however long you like between layers - there is no set time to wait, merely the fact that the longer the paint sits, the further along it is in polymerization, the less vulnerable underlying layers are to lifting. The drawback is not everyone wants to wait between layers. I apply anywhere from 10 to 50 layers in a day; the potential to rapidly apply many layers (opaque color, glazes, scumbles, splatters, whatever) is one of the reasons I work in egg tempera. But to do this successfully I’ve had to learn how to apply the paint in such a way that I don’t lift underlying layers. This takes practice.

What is your “varnish”? Adding a varnish to paint is generally not a good idea for several reasons: most varnishes tend to yellow, grow brittle with age, and if a painting is cleaned at a future date, solvents used to clean the varnish on top will also dissolve the varnish within the paint, thus destroying the paint films. Also, turpentine is a fairly noxious substance. If you want to work with it healthfully, make sure you have adequate ventilation in your studio. I don’t mean to tell you how to paint. Materials and working methods are entirely personal choices and you may (as many people do) add varnish to your medium and use turps – I just want to be sure you are aware of the drawbacks.

Hope that helps!

Koo
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