To polish black marble, the wrought surface is rubbed with fine sharp sand and water until all the marks of the chisel or saw are removed and an even face is produced, it is then grounded - that is, rubbed with grit stones of varying degrees of fineness, commencing with the coarse or first grit, next the second grit, which is a little finer, and finishing with snake stone or water-of-Ayr stone. Particular care must be taken in each process of gritting that the marks or scratches of its predecessor are removed, so that when the surface is "snaked" no scratches are visible. Then rub with a boss or pad of worsted material sprinkled with flour emery and moistened with water, and finally with a pad of felt sprinkled with putty powder (calcined tin). The chief factor in producing a good polish is persistent and attentive rubbing. An imperfect polish may be due to the slab not being properly grounded or gritted, which is the case if, on looking closely into the polish, small scratches are visible all over the sur-face; it must then be almost entirely repolished.

If the polish is dull only, then the slab has not been sufficiently rutabsd with the felt.