
Originally Posted by
The Mechanics' magazine, museum, register, journal, and gazette
17. Is a dark slate of very uniform character; in appearance not at all laminated; is in considerable use among jewellers, clock- makers, and other workers in silver and metal, for polishing off tbeir work, and for whose greater convenience it is cut into lengths of about 6 inches, and from a quarter of an inch to an inch or more wide, and packed up in small bundles of from 6 to 16 in each, and secured by means of withes of osier, and in that state imported for use, and called blue polishing-stones.
18. Is a stone of very similar properties, but of a somewhat coarser texture and paler colours, and thence termed grey polishing- stone. Its uses are the same, and they are manufactured near Ratisbon.