On a 11 X 15 4 ply cold-press black mat, I injected minerals to fill the black fibers of the mat to allow the color to be seen. In order to see anything other than white gypsum crystals, you have to fill the voids of the fibers completely full.Then I poured a poly-glass mix lightly on the mineral work. This not only keeps the minerals from working themselves back out. It gives a high gloss appearance looking like a glass portal. To get an illusion of stars I took a small part of the Gypsum Crystal and drove slivers of Crystals into the fibers.