I have an old article from Art and Activities or School Art and I have used
this techniques for a couple of years. It was called antique crayons. You
have students sketch on white drawing paper and when the drawing is finished
you go over the lines with black permanent marker. You color it very hard
with crayon and it does need to be smooth and thick. When you are finished you
go over it with black tempera and you rub it off with cotton balls. It needs
to shine. My 4th graders have a hard time getting the paint off because the
crayon is not heavy or the put too much paint. These are really beautiful.
The paint can be put on with cotton balls little by little and it needs to be
rubbed while it is damp.