A grinding plate is a piece of glass or marble that has a frosted surface. This is where you grind pigment to create a paint. You don’t need a large grinding plate for the amount of pigment used with our kits. We have a 4×4” piece of tempered frosted glass, on which to grind powdered pigments with our mini-mullers. Some artists use several grinding plates and mini-mullers if they are working on a multi-colored project. Otherwise, simply wipe the grinding plate clean when necessary.