For the best sound, always keep your slate, glass, and crystal friction calls conditioned. Slate calls can be conditioned with Scotch Brite pads that can be found at most stores like Walmart or Home Depot. Simply run the Scotch Brite pad back and forth over the call’s surface. Scotch Brite can also be used to clean the tips of your striker – you really don’t want to use sandpaper! Sandpaper can change the shape of the striker’s tip. For glass and crystal calls, I recommend using a conditioning stone like David does in this video, but you can also use drywall sandpaper.