The first step in prepping the slate is, of course, cleaning it. As for the cloth covering it, the slate is usually full of dust, too. If the felt glue was holding the felt, you will probably find some excess on the slate as well. Scrape it off gently, then wipe the slate off using a dry cloth. Water and cleaning products are not a good idea to use on slate, as they will penetrate the material, making it less durable. Although slate is quite an endurable material, it still requires some level of care.