I tried casein printing many years ago. A friend of mine, Jerry Ellison,was in contact with Franklin Enos (see article: http://unblinkingeye.com/Articles/Casein/casein.html) who was the undisputed master of casein printing. Jerry shared Franklin's formulas and procedures with me, and we both attempted to reproduce his results. While I was able to make images that were on a par with gum prints, I was never able to achieve the long tonal range prints that were standard for Enos. I have a single example of Mr. Enos's work that is nothing short of magic if you consider it was done in one printing.
In hindsight, I think the problems that we experienced were directly related to the quality of the casein that we were using. We prepared our casein, starting with powdered milk, as described in the article I referenced. Whether it was a function of the powdered milk we used, or the ammonia, I don't think we obtained very good casein. Since I did not communicate directly with Mr. Enos, I have no idea if he employed this method of making casein, or if he obtained it in some other manner.
Anyway, that was my experience. If you can figure out how to achieve a long tonal range, this process is capable of excellent results.