Pearl, a hard, white, glossy, and roundish concretion, which is usually found in the shell of the East-Indian pearl-oyster; though it is also occasionally met with in the shell-fish of Europe.—About the middle of the last century, a very extensive fishery was carried on, in the rivers communicating with lakes in the northern parts' of Scotland ; whence London was supplied with a considerable number of pearls, that were little inferior to those of the East ; but this-source of wealth is at present exhausted.
Pearls are formed of the same matter as the inner shell of the fish in which they are found ; and consist of several coats spread with the greatest regularity over each other, in a manner similar to those* of an onion. The most esteemed and true form of pearls is, a complete sphere ; though they are sometimes pear-shaped, and of a considerable size, according to which their value rises progressively : as they serve for ear-rings, and other ornaments. They ought to possess a pure white lustre, perfectly clear from spots or stain- ; and their surface should be smooth and glossy ; having a beautiful natural polish, which no art can improve.—The finest pearls are imported from the East; and, like rubies, etc. may be brought to England from any place, and in any ships, free from all duty.
Artificial. Pearls :—As the genuine pearls are sold at an extravagant price, ingenious men have contrived methods of imitating them so completely, that they can scarcely be distinguished from those collected in the East. The principal ingredient, employed for this purpose, remained a profound secret for many years ; but it is now ascertained, that it Consists of the fine silvery matter, which is found on the lower side of the scales of the blay, or bleak-fish (Cyprinus alburnus, L.). These scales are first removed; then washed re-peatedly in pure water ; -and,after' A the different liquors have subsided, the fluid part is carefully decanted ; when a pearly matter, of an oily consistence,remains at the bottom; which is denominated by the French, Essence d'orient. A small portion of this matter is dropped in a hollow blueish glass-bead, that is gently agitated, till the whole internal surface is completely lined ; when the cavity is filled up with wax, in order to impart solidity and weight. Pearls thus manufactured, possess fewer blemishes than such as are natural or genuine, to which they are fully equal, in point of brilliancy.