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Moderator Answer
(koo schadler)
Egg tempera is a high PVC paint - it has a high ratio of pigments to binder. High PVC paints are less flexible (since binders bend [to varying degrees] but pigments don't). The more layers applied, the less flexible the paint film. Additionally, egg tempera becomes more brittle with age because the lipids in egg yolk (which give plasticity to the paint film) remain mobile and move around, sometimes exiting the paint film. For these reasons, egg tempera is considered a less flexible paint that is most durable when applied to rigid supports (such as wood-based panels).
This doesn't mean egg tempera can't be applied to paper - it's physically possible to do so. With age (especially if there are a lot of paint layers) a flex of the paper or swelling caused by humidity could potentially cause the paint to crack and eventually fall off (I've seen it happen). The problem with egg tempera on paper isn't how it looks and behaves today (it generally behaves quite well), but how it appears in a month, year or decade.
Nonetheless, many people paint in ET on paper, and many don't run into any problems. I often hear from painters who paint ET on paper with success (although it can take time for problems to occur...). Afterall, a poorly made painting can last centuries under optimal conditions, a perfectly made painting fall apart under adverse circumstances. So you are free to paint ET on paper with the understanding that it's not necessarily a "best practice".
To help the painting last longer, I would....
- Paint thinly (no thick paint or impasto), more like watercolor or gouache.
- Apply just a few layers (not the dozens or more layers that many ET artists apply)
- Avoid large micron size colors (anything above perhaps 5 to 10 microns - i.e. don't use a roughly ground, historical lapis lazuli or dioptasio; I've seen large particle size pigments crack when applied to parchment, which really flexes in response to humidity).
- The thicker the paper, the less it flexes, the more stability that gives the paint.
- Some people apply a thin layer of gesso (animal glue & chalk) or just plain animal glue to the paper beforehand, but I don't think it's necessary; it would just contribute more brittleness. If you work thinly, the egg tempera will sink into and adhere to the tooth in the paper sufficiently well.
Good luck with your project!
