SLATE. - The ordinary slate used for building purposes does not admit of being highly polished, but it is rubbed smooth, first with an iron plate fed with sharp river sand and water, and then with lumps of gritstones, of which two or three kinds gradually finer one than the other, are also used with water. The rubstones employed, depend principally on their relative abundance in the respective districts.
A lump of pumice-stone leaves a grain on slate suitable for writing upon, and the greyness is removed either by a slight rub of oil, or what is better a wash of common writing ink allowed to dry on. A disk of slate cemented to a wood chuck is useful to the amateur for receiving in the lathe rough sketches of eccentric patterns, and slate also serves for drawing boards.
As noticed in vol. 1, page 165, slate has been recently employed for chimney pieces, internal decoration and furniture, in which case it is rubbed smooth, then japanned like black and other marbles, and also of all colours and devices, after the manner of tea trays; when the objects have been baked to harden the japan they are first smoothed with pumice-stone, and then polished with rottenstone, after the ordinary mode described under Japanned Works.