Rainbow Obsidian: The Ultimate Guide to Meaning ... The sandpaper used in the process is 600, 1200 and 3000 grit paper. Edges of the stone are buff using 600 grit sandpaper. It removes large imperfections on the surface of the obsidian. 1200 and 3000 grit sandpapers are used respectively afterward to provide it with a shiny, scratch-less surface.