glossy, chalk-covered cardboard on which, after coating with ink, line drawings can be made by scratching through the ink to the white surface
See scratchboard in American Heritage Dictionary 4
(skrăchˈbôrdˌ, -bōrdˌ)
noun
A drawing board coated with white clay and a surface layer of black ink that is scratched or scraped away to produce an effect similar to engraving. Also called scraperboard.