The "printmaking with kids" suggestions were great. On collographs, they
wipe best if the finished plates are coated with an acrylic medium first and
let dry. You may have to coat both sides if the plate isn't rigid, to keep
it from warping too much. Beveled matboard scraps are perfect for
collographs, as is old X-ray film. I like the matboard because you can both
build up and cut into - (even clear through the matboard isn't too deep, and
you'll get sharp uninked debossed shapes). you can also just cut a line
around the shape you want and peel up different thicknesses of the matboard.
The local framer probably tosses armloads of scraps every week. Be sure the
edges of any plates you make are beveled (and clean - a little solvent on a
q-tip will help a lot). it looks better and is safer for the paper and
I consider the Ross & Romano printmaking book the primary source for "how
to" collograph. The technique looks dated to me, because the artists who
used it so much were of "a time". But it still has a lot to offer.