I use green scotchbrite on my slate calls. Google scotchbrite pads and click the shopping tab. You can find them at lots of online sellers. You should be able to find them at any Lowe's or hardware store near the sandpaper. You can also check walmart near the dish soap and stuff. Condition slates whenever you begin to notice quite a few marks from the striker or when your striker no longer grips the surface as it should. Condition the striker tip when it begins to have a dark buildup from slate or a glossy appearance if running it on glass or aluminum. I use 120 grit sandpaper on glass calls and striker tips.