Casein paint is permeable and not washable. Very stable, with a good coverage, it only becomes opaque after drying. It has been used for centuries to beautify and protect woodwork, furniture and walls. It can be applied on all supports (mineral, plaster, plasterboard, old paint not lacquered...). However be careful to not apply it in damp parts.
Basic recipe :
1) In a small bucket or saucepan, pour 2 litres of water ; mix with a whisk 300 g of casein to dissolve any lumps.
2) Add 80 g of alum salt, stirring vigorously with the spatula. The mixture will thicken and become translucent. Put it aside and let it rest 2 hours.
3) Meanwhile, pour 2.50 litres of water into a large bucket with 6 kg of white Meudon powder and mix with the electric stirrer to obtain a thick mixture.
4) After 2 hours, pour the contents of the small bucket into the large one, and mix. Add the previously wet pigments to the water and mix to obtain a homogeneous colour. To obtain stronger colours, reduce the dose of Meudon white.
Let it rest 1/2 hour. The mixture is ready to be used. Apply 1 or 2 coats with spalter (wide brush) or roller.
Recipe by Antoine Bosse-Platière