You have this medium in many different types and color shades. white, black and in effect pastes. You can use the pastes through stencils with a spatula, let it dry well and then this is a wonderful base to work over.

You can clean your stencils by wiping most of the paste immediately with a paper towel or the like and afterwards you can clean them with lukewarm water (not hot, because then your stencils shrink) or let them soak in a little biotex.