Re: Useful Casein Text
Casein emulsifies with oil quite well, and I've used it often. It isn't required when making casein paint, but adding a small amount of oil can help alter the texture of the paint and make it more "buttery" as well as slowing the drying time some and making it easier to blend, aspects of oil. A lighter weight oil, like safflower or poppy works well in general, but if the intent is for undertones of an oil painting, I would recommend mixing linseed for the initial layer.
Reading her text, I would add that care should be taken to avoid the term "drying the oil" when talking about casein emulsion, since casein isn't a dryer. Instead, the oil is held in place by the dry casein as the oil continues to oxidize. This is one of the advantages of using casein emulsion in the beginning with oil, since you're not diluting or weakening it as you might with solvents, but actually thinning the oil and adding a glue.