MITRA Forum Question Details

It would be difficult to apply the egg tempera and not have it pick up the gouache. This would also be true when you applied the egg water.

Perhaps you could isolate with B-72 but this may cut the adhesion too much and could result in paint delamination. Please experiment on mock ups before attempting this on your artwork. My gut feeling is that it is not a great idea.

​Agreed with Brian on all points.  You could try lightly, quickly sponging on an isolating layer of egg yolk + water (not too thick a layer of yolk; about 1 part yolk to 8 parts water, in that ballpark).  A sponge allows for a more rapid, dabbing, on and off of the medium, which may mitigate lifting...but it's more likely that the application of a water-based layer atop gouache, regardless of the tool with which it's applied, will lift/smear the gouache.  

You could try applying a very thin layer of shellac (about 1 part bleached, ultra blonde, de-waxed shellac flakes to 8 or 10 parts alcohol). It wouldn't lift the goauche - but shellac would decrease adhesion of egg tempera to the panel; still, it might work.  Shellac, however, has other foibles, as discussed in other MITRA posts.  As always, experiment before diving in with either of these options.

​Koo Schadler