[alt-photo] strange flaking with casein prints

[Matti Koskinen]

hi,

I've done recently casein prints using acrylic paints, and till yesterday with various success., sometimes really good results. I have used always the same mixture of casein (made from cottage cheese and ammonia) + equal amount of casein and pot dichromate + black acrylic paint. I've used the same method to develop, first soaking the print abt. 5 mins in lukewarm water and then roller developing with diluted dish washing liquid like tempera prints. Tempera prints have never stick well on the paper like casein. I size the paper with PVAc. First 1 part glue + 3 parts water, let it dry, then another coating with 1 part glue and 1 part water. Have worked fine. Diluted gesso leaves too uneven coat. Yesterday the print was all black, no colour got off. Day before yesterday just ok. I think the problem was too hot hairdryer. Now I made a new print, coating A3 paper and cutting into two A4, just to test the first piece. It flaked really badly. Only the dark parts of print stayed on the paper. I increased the exposure time. Better result, but bad flaking. The print was very contrasty, only black and white, and the white parts got off with bad flaking. Earlier the prints have showed nice tones from pure black to white.
 
One thing I can think of is that the glue sizing was probably bit humid with the succeeded prints, and thus the casein stuck on the paper. Even long exposures (normally 3-4 mins) but even with 15 to 20 mins develop fine, though it needs more force to the roller and takes much longer to develop, but finally the image on the paper comes out fine.

But now just bad flaking and contrasty prints. The tap water comes from hundred meter deep drilled well, so the water is not always the same, it changes every now and then. I have somewhere a pH meter,  but not found it yet from the pile of junk including lenses, cables, amplifiers, computer parts etc.

Any ideas?

tnx

-matti