isolating layer for oil glazes

[otto]

Not sure how many of you use oil glazes over your ET paintings. If you do, do you find it necessary to isolate the tempera with shellac or dammar? Or, as some suggest, find ET to be a good surface to paint oil glaze directly on? Thanks!

[turlogh]

Not sure how many of you use oil glazes over your ET paintings. If you do, do you find it necessary to isolate the tempera with shellac or dammar? Or, as some suggest, find ET to be a good surface to paint oil glaze directly on? Thanks!
ET can be a little difficult to paint directly over with oil. The ET is so lean that it sucks some oil out of the paint, making a surface that is disagreeable to work on. The easiest option is to apply a very thin layer of oil to the surface, wiping as much of it off as possible and then working into the wet surface. Jan Van Eyck did this with some of the earliest "oil" paintings and his work has survived very well with no significant yellowing and only the normal amount of cracking. This is the method I most commonly use.

[odyssic]

Couldn't one also slowly add oil to the upper layers and make the transition into oil paint slow and steady?

Steven

[turlogh]

Couldn't one also slowly add oil to the upper layers and make the transition into oil paint slow and steady?
You can certainly do that by making emulsions with increasingly greater amounts of oil for each layer. However, I would tend to do this only because I thought it would help me to paint better, not because I thought it was necessary for craftsmanship. Straight oil over straight tempera is a simpler method and has clearly stood the test of time.