Things I learned
Mica has different colors and can be ground into different grades. The 40 mesh from Continental Clay is used in raku clay bodies. It does not have much shine for clay plasters or clay paints. It does, however, make clay plasters very workable. It can be substituted for sand or used in addition to sand in a clay plaster recipe.
So, I just mixed some 40 mesh black mica with a red clay slip and some fibers to make a plaster for one of my forked branch vessels. There is some shine. I like the subtle shine. When I mixed it with white clay, it was like adding graphite. It made it very dark.