would they have used milk paints lik the celts
here,s a formla formilk paints(never tried it myself tho)
* 1 Quart skim milk (room temperature)
* 1 Once of hydrated lime by weight (Available at building centers. Do not use quick lime, as it will react with the water and heat up. Hydrated lime has been soaked in water then dried.)
* 1 to 2 1/2 pounds of chalk may also be added as a filler.
Stir in enough skim milk to hydrated lime to make a cream. Add balance of skim milk. Now add sufficient amount of powder pigment to desired color and consistency (Pigment powder must be lime-proof). Stir in well for a few minutes before using. For best results continue to stir throughout use.
Apply milk paint with a cheap natural bristle brush. Allow project to dry sufficiently before applying next coat.