Re: Casein: History and Resources
Acrylic paints or mediums mix just fine with casein. The combination is often recommended for the reasons you describe, adding the benefits of both mediums. One particular shortcoming of casein is that you shouldn't apply a layer too thickly. However, if you've mixed in 50% acrylic polymer, that's not a problem.
Personally, I see the fast and permanent drying characteristic of acrylics as more of a problem than a benefit. Well, "problem" probably isn't the right word. It's just something you're forced to handle.
One thing I'd recommend is to be sure your mixture is well combined before you use it. Don't just dip your brush in both and start painting. Also, pay attention to what is in your mixture. If you dilute it with water in some passages, I'd suggest adding some acrylic medium also to improve adhesion. In fact, you might be able to get the effect you're after without using acrylic paint and just add medium to the casein.