I am going on 53 years old and I remember MY seventh grade art teacher using
the chalk and buttermilk technique. We drew still lifes. So, it has been
around for awhile. (Can't recall WHY we did it this way, but I do remember
having fun.)
I also remember reading in a book once about a technique where you sprinkle
white POWDER tempera paint on damp paper, and then work into the paint with
colored chalk. This creates some interesting pastel colors and impasto effects.
Also, there is little smearing once it dries.