For the underpainting emulsion done with the thin linseed oil you can use a water diluted 5:1 pure casine liquid or non-fat milk. To thicken the mixture use non-fat milk powder. Of course you can use dry pigments with only the dry non-fat milk and store each color separately, just add water. I like the gloss emulsion mix better.
Use this thin mixture very thinly first, to seal the support. When that's dry in two minutes use this thin mixture in the underpainting. Mix it 1:1 with the tubed oil paint, it sets very fast.
Use the non-fat milk as a thinner.
Three parts stand oil or sun-dried oil is mixed with two parts of the liquid wet and dried powdered skim non-fat milk. Store this emulsion to add to the oil paint in a 1:1 mixture.
Use this thicker emulsion to paint with. You will like its fast setting time and gloss.
Day 0, drawing. Day 1 painting,