I know casein as curd mixed with lime for wall painting in historical buildings. The silicate paint I used is quite similar. But I have to do a few more tests first anyway to find out what the problem was. then I can also try casein. Thanks for the idea!
Best regards
Arndt
My career was in the conservation of Historic Buildings and Ancient Monuments

Which is why I thought of casein and as you say it is usually mixed with slaked lime ( Calcium hydroxide ) to form a glue/paint. Cuttlefish bone is mainly made of Aragonite which is a natural form of calcium carbonate, therefore the casein lime mix will bond well with the aragonite and actually strengthen it.