Before we humans made paint with oil (or our modern latex), paint was made with a variety of ingredients. Paint has to have something that provides color like ochre or, during colonial times in the USA, brick dust, and a medium for the color that provides stability and hopefully durability. Egg yolks was at one time used for paint. Anyone who has tried to scrub hardened egg yolks off a plate knows that egg hardens to something like cement. But it does wash off in water.
Another substance used in paint was milk. Since most people lived on farms up until the present, milk was something readily obtainable. We know that milk paint was used. Occasionally antique furniture and old houses in this country are discovered to have been painted with milk paint.
However, the recipe for milk paint is very important. In 1801 a French artist described painting with a milk paint and wrote that it was not durable. Among other things, it came off with the slightest friction (Don’t ever brush against it or it would come off on one’s clothing, and would dissolve in wet weather.) And milk paint must be used right away. It has a short shelf life.
The important ingredient is the protein casein. Sometimes borax is used to the lime to help dissolve the casein. Different recipes have been tried to make milk paint durable. We know that at least some of them were successful; surfaces painted with milk have been discovered in some old houses. It has a hard very smooth finish and was usually in pale pastel colors. It is impervious to paint strippers and is difficult to paint over. It is totally non-toxic, though, and can be used to give furniture an antique look.
Oh, and one final fun fact. House painters in the past did not ‘paint’; they distempered the walls.