I threw a couple tubes of casein—black and white—into my kit this morning on the way to the diner.
While waiting for my scrambled eggs, I did this little study of the creamer. Casein is well suited to this kind of rendering because you can match tones and textures very closely.
For Anton on FB, here's more about the tools I was using:
I was using Richeson / Shiva casein
1/4 inch flat brush
Moleskine watercolor notebook
Waterman Phileas red fountain pen
Lots of info on casein at Richeson's FAQ about casein