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