(a) Marine shells are cleaned by rubbing with a rag dipped in common hydrochloric acid till the outer dull skin is removed, washing in warm water, drying in hot saw-dust, and polishing with chamois leather. Those shells which have no natural polished surface may either be varnished or rubbed with a little tripoli powder and turpentine on wash-leather, then fine tripoli alone, and lastly with a little fine olive oil, bringing up the surface with the chamois as before.

(6) The shells are first boiled in a strong solution of potash, then ground on wheels, sometimes through one stratum to show an underlying one, then polished with hydrochloric acid and putty powder. In this operation the hands are in great danger. Shell grinders are generally almost cripples in their hands.

Slate

Slate is faced first with an iron plate with river sand and water, smoothed with pumice; then japanned and baked to harden the japan, and again smoothed with pumice and polished with rotten-stone.