Combining egg tempera and oil glazes.

Let’s break this down into the various components of your question. 1) It is not necessary to seal/isolate the egg tempera. The degree to which the oil paint will or will not sink in will have much to do with how many layers of egg tempera paint you have applied. However, for good adhesion it is not a bad thing to have SOME of the oil absorbed into the egg tempera below. If you are looking for a very brushable and extremely fluid application of your oil paint layers then you could isolate the tempera with some sort of coating. Bleached shellac is a possibility…as an isolation layer (which will eventually be covered by pigmented layers) is fine as opposed to it being used as a final surface coating, something that we do not recommend. An extremely thin layer of an oil-containing medium is also possible….please see our “Sinking-in” section in our “Varnishes” document. 2) If one wants to be a VERY cautious tempera painter you can let it dry for up to a week. However, we feel that allowing the paint to dry for a couple of days is sufficient. 3) It is not necessary to use any one particular medium. Oleogel is an option as is Liquin as other mediums. Just avoid any mediums containing significant amounts of soft resins (e.g. dammar, mastic).