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Acid or Rennet Casein

Acid casein is produced by adding citric acid or similar to milk. 

Rennet casein is produced by adding an enzyme to precipitate the casein.

For most craft purposes and users, there is little difference between the two. For some more specialist applications it is worth investigating which works best for you. 

Rennet casein can retain some additional calcium. This can change how the product dissolves and reacts to other additives like Borax.

Casein Powder

The particle size is the next factor. This is how small the powder grains are. Typically the smaller the mesh size, the bigger the particle. A 30 mesh powder will be coarser than a 200 mesh.

A medium grain casein is your most versatile product. A 30 mesh powder can bed used to create a range of base liquids and can make an excellent glue, varnish and paint. 

Finer grain casein powder (100 mesh and upwards) is typically more expensive and can have a whiter base colour. It can be easier to dissolve and mix and can produce a smoother product.

Casein Glue

A simple recipe for a ready-to-use casein glue is as follows:

400ml water

80g 30 mesh casein dispersed (1 hour)

Add alkali (i.e sodium hydroxide) to pH 7-8

This should form a viscous mass that is ready to use and will last a day or two.

 

Casein Paint

A basic recipe for creating milk paint is below. This creates a thinner liquid. The final colour will depend on the amount of "white" and pigment added.

500 ml water (total, including pigment wetting)

60 g 30 mesh casein dispersed (1 hour)

120–200 g chalk/whiting (or marble dust) as the main body/opacity

Pigment: 10–40 g (to colour) — start low and increase

Add alkali (i.e. borax solution or hydrated lime) to pH 8–9