I have taught this class...
first wash some regular muslin to remove oils, dirt finishes, etc..
the iron onto freezer paper...
use only real crayolo crayons...trace your design onto the muslin using a sharp #2 pencil, or a micron pen if you want the black to show...like a stained glass, etc.
color lightly building up color as you go..you can even shade if you like...mixing colors, etc...
the place a thick white paper towel over the crayon and press...not too hot, but hot...let cool and color again...
you do this until you achieve the look you want..
I just love it..great for holiday stuff...
you can get millions of designs at color book pages online..FREE