The process of enamelling slate, as for instance a mantelshelf, is as follows. A dark lacquer or tar varnish is applied with a brush to the surface of the slate, which is then placed in an oven and baked from twelve to forty hours, according to size, the heat being just sufficient to fuse the lacquer. The shite is then treated with a coat of enamel, and again placed in the oven to harden. This is repeated several times till the surface is perfect and the slab is ready for polishing, which is effected by rubbing with woollen bosses and powdered pumice-stone, finishing off with a little powdered rotten-stone. Scratches cannot be effectually removed from a polished (enamelled) slate mantelshelf; rubbing with an oily rag will, however, soften down the scratches. The only real remedy will be to have the shelf re-enamelled.