Cleanliness should be most scrupulously observed in polishing. This remark may appear misemployed as regards a process in which various dark-coloured powders, etc. are mingled with oil or water somewhat like the pigments used by artists, and are so employed, that the hands must almost inevitably become more or less soiled; but that degree of care and order must at any rate be adhered to, which will entirely avoid the different powders and materials becoming mixed. The finest powder, if mingled with the coarse, would be comparatively inert and harmless, but a grain or two of the coarse powders, if accidentally present along with the fine, would inflict deep scratches, and completely nullify the efforts at obtaining a highly polished surface.

On this account it is desirable not only to keep the various polishing tools and powders carefully separated in boxes or bottles, but also before proceeding to each finer stage of the process, carefully to wipe or even to rinse the work in water, for the entire removal of all the previous materials employed in the earlier stages of polishing.

Having advanced these preliminary and general remarks, we shall at once proceed to the descriptive and general Catalogue, deferring until the subsequent chapters a variety of additional matters of a more specific character.