Recently obtained some Crescent RendR paper and had been trying various media when I discovered that watercolor seems to have some distinct flaws. In an effort to make the watercolor work a bit better on this paper, I decided to put a couple coats of Casein emulsion, diluted with water to a thin consistency on the paper. The paper took a surprisingly long time to dry and I needed to clip it down so that it would dry flat. After 2 weeks of allowing my coats to dry thoroughly, I painted on the pages with watercolor and was happily surprised to find that it took the watercolor in a completely different way.

Before priming, I cannot really lift color on this paper very well, everything stains very heavily into the surface. Layering watercolor resulted in progressively getting darker and not mixing very well. Color pooling at edges and drifting back into others but not blending was common.

After priming, I can now lift colors just by dampening them and blotting with a paper towel or by putting water down and then using a dry brush to soak up the color. Layering watercolor results in colors blending and mixing. Color no longer pools at edges (with the accompanying drying edge splotches), blending is simple and edges are very easy to control.

So, as a size, Casein works amazingly for making surfaces resistant to water being deeply absorbed into the surface. It also keeps the surface protected, coating the fibers and keeping them from being as susceptible to oxidation. If you happen to have a large amount of paper lying around that you need to use, sizing it with Casein for use with other media is a great way to put it to good use.