Silicon Carbide is a perfect tool for flattening and lapping synthetic and natural stones. Flattening & Lapping Kit includes 4 bottles of Silicon Carbide powder (F 60, F 120, F 220 and F 400 grit) and glass 8"x8".
The SiC powder should always be coarsier than a sharpening stone.
Take slate pencil and put crosshatch pattern to the surface of the stone. Never skip this step. Your goal is to get rid of crosshatch completely. If you notice left-over of pattern somewhere, it means geometry is not flat yet.
Always add water to make suspension, not dry SiC. Try to use glass area evenly. Your glass will wear over time, because SiC affect glass too.
For hard stones, coarse SiC will be the major time consumer. When SiC disintegrates, put another pinch (refresh). If there is too much suspension, clean your glass. Use straight edge or metal ruler to check flatness. If you are not sure, make crosshatch pattern again.
The abrasive hygiene should be a priority. Don't let single coarse particle to remain in fine lapping.
If you have a question regarding this product, please feel free to ask.