Mother Of Pearl

MOTHER OF PEARL. - See Shells. NACREOUS SHELLS. - Idem.

Norway Ragstone

NORWAY RAGSTONE. See Hone Slates, article 1.

Onyx

ONYX, a variety of Chalcedony that is wrought by the lapidary like Carnelian.

Opal

OPAL. - This beautiful iridescent gem, although soft is very brittle and tender, on account of the numerous fissures by which it is traversed, and that apparently give rise to the splendid play of colours seen in precious opals of fine quality. Opals are always cut with rounded faces, and are more generally treated like alabaster than carnelian.

Oxides Of Lead And Tin

OXIDES OF LEAD AND TIN. - See Putty Powder.

Painted Works

PAINTED WORKS, such as the panels of carriages,are first grounded, or carefully painted three or four times in good oil colour, and when thoroughly dry and hard, the surface of the paint is rubbed smooth with a lump of pumice-stone plentifully supplied with water; two pieces of pumice-stone are used and continually rubbed together to remove the paint accumulated on their surfaces. The finishing colour, which is frequently ground up in varnish, instead of oil, is then laid on, and the panels after having had three or four coats of carriage varnish, (a description of copal varnish,) are carefully polished first with a rag supplied with pulverized pumice-stone and water, and then with rottenstone and oil on other rubbers: the worsted stocking being here likewise in great requisition for the purpose.

Palladium

PALLADIUM. - Palladium, platinum and silver when inlaid in the limbs of mathematical instruments, are treated much the same as platinum, which see.

Pastes

PASTES, or factitious gems made in coloured glass, are polished after the mode employed for the gems themselves, and the succession of the mills and powders used by the lapidary for the purpose is nearly the same as that described under Cabnelian. Facets on pastes, are cut on a lead mill with flour emery, and polished on pewter with rottenstone, but the particulars of this part of the lapidaries' art will be found in Chap. XXXIV. The description of the principal Factitious Diamonds will be found under Diamond, article 5.

Pearl Shell

PEARL SHELL, or Mother of Pearl. - See Shells.

Pebbles

PEBBLES. - Although these differ much in their colour and general appearance, they may be viewed as varieties of Agate, and are treated as such, or in the mode fully described under the head Carnelian.

Peridot

PERIDOT. - See Chrysolite.

Pewter

PEWTER is seldom polished; the articles when left from the turning tool or scraper, are burnished with plenty of oil, the oil is removed with a rag and whiting, and this is the only polish given. Pewter vessels are mostly cleaned with silver sand and water, or with liquids containing potash or soda, to remove the grease. Pewter is much used for laps and polishers by lapidaries, jewellers, watchmakers and many others. The metal of old pewter plates is preferred, but tin unalloyed appears to be nearly identical in effect.