Generally, shells to be preserved and polished may be divided into (a) those having a natural polish and requiring very little preparation (b) those which have no natural polish, but which may be polished without much trouble; and (c) rough shells which require to be smoothed by mechanical means before polishing. Some of those in the first class, especially when found with a glossy surface, look well if merely cleaned; with others the colours and polish will not be so bright when dry as in a wet state, so they are coated with gum water, white of egg, or colourless transparent varnish. The polish and colour of some shells is obscured by a dull epidermis or outer skin, to remove which, soak in warm water and rub off with a brush or a rag dipped in hydrochloric acid; afterwards, well wash the shells in water and proceed as before. If, after removing the skin,the shells have no natural polish, they constitute the second class. Next wash them well in warm water and dry in hot sawdust; some may be polished by simply rubbing with chamois leather, with or without a little olive oil. Others are smoothed with emery-paper, rubbed with washleather dipped in turpentine and dressed with tripoli powder, then with tine tripoli alone, and finally with olive oil and chamois leather.

All rough shells should first be boiled in a strong solution of potash. Ordinary files, followed by emery-cloth, will remove the roughness of some shells, which can then be polished in the way meutioned for the second class. Others must be ground with emery-wheels of different degrees of fineness, or wooden and other discs dressed with washed emery, rottenstone, and water; or the disc may be covered with leather dressed with putty powder or tripoli. Sometimes, in grinding shells, the outer stratum or strata is ground through to show the underlying ones.