The tile tool is used for Fine grinding of the mirror blank. You can use another, possibly thiner glass blank as the tool but a Dental Stone tool is cheaper. Traditionally Plaster Of Paris has been used for this, but dental stone has some advantages. Dental Stone does not need to be sealed, it does not contain sand or other gritty materal that could scratch the glass and it does not chip. Since it does not need to be sealed you may pour the stone right on top of the back of the tile mat, bonding them together without epoxy.
