I do this too. I have also done it on rectangles of masonite board, on
cookie sheets, on mirrors, and on plexiglass, and on cutting boards. I
like using bumpy "backgrounds" too, to pick up additional texture.
>I have Formica tables in my art room. I've had students paint them directly >with finger-paint or tempera with liquid soap in it, lay paper over it, rub >and lift for a simple monoprint. They learn about reversal pretty quickly. >It's also interesting to use wet and dry paper for the same process so they >see the textural differences. Marbling is also a type of monoprint. Linda