Over the last two years I have developed a technique of applying a solid color such as iron oxide orange on wet plaster and after the plaster has dried (2 to 7 days) continuing with fresco friendly pigments mixed with eggyolk. Some of the paintings are in perfect condition but I just got back several from a gallery (and I have had the same thing happen at home) and paint has flaked off in random spots bringing the iron oxide orange with it exposing the white plaster. Does anyone have experience with this? Has anyone had better luck using casein? When I am painting the images on the dry fresco I like to sponge off colors leaving a trace and then apply new colors on top so it gets wet at times. But many paintings haven't had problems in these areas so I am mystified. You can see the paintings if it would help on www.palmerpaintings.com/phyllis

Here is what happened:

You perhaps, put red oxide too "thick" so there has been little adhesion to the intonaco. Paints for buon fresco have to be very thin, somwhat of an "ink consistency" especialy at the beginning of the day. You need to apply several very thin coats to build the color. Also adding a little lime to the paint helps adhesion.

In your case I would suggest using "pompeian method" of simply adding red oxide to the plaster itself.

Thanks so much for responding and especially addressing the issue of the oxide red fresco layer being pulled off, I will try thinner layers next time. I would also like to try adding the color to the intonaco layer. Do you add it as paste or as powder? Is there a formula for the amount to add or do you do it by eye? After all it dries lighter. Let me know, thank you, Phyllis

add it as powder to dry sand and mix well, then add lime putty

Thanks so much for your suggestion. I' ready to start.