PEARL, in Natural History, a hard, white, shining body, usually roundish, found in a testaceous fish, a species of Mya. Pearls, though esteemed of the number of gems, and highly valued in all ages, proceed only from a distemper in the animal which produces them, analogous to the bezoars and other stony concretions in several animals of different kinds. Mr Bruce mentions muscles found in the salt springs of the Nubian desert, in many of which he observed those excrescences which might be called pearls, but all of them ill formed, foul, and of a bad colour, though of the same consistence, and lodged in the same part of the body, as those of the sea. “The muscle,” says he, “is in every respect similar, I think larger. The outer skin or covering of it is of a vivid green. Upon removing this, which is the epidermis, what next appears is a beautiful pink without gloss, and seemingly of a calcareous nature. Below this, the mother-of-pearl, which is undermost, is a white without lustre, partaking much of the blue and very little of the red; and this is all the difference I observed between it and the pearl-bearing muscle of the Red Sea.”

In Scotland, especially to the northward, in all rivers running from lakes, there are found muscles which have pearls of more than ordinary merit, though seldom of large size. They were formerly tolerably cheap, but the wearing of real pearls having come into fashion, those of Scotland have increased in price greatly beyond their value, and superior often to the price of oriental ones when bought in the East. The reason of this is a demand from London, where they are actually employed in work, and sold as oriental. But the excellency of all glass or paste manufactory, it is likely, will keep the price of this article, and the demand for it, within bounds, when every lady has it in her power to wear in her ears, for the price of sixpence, a pearl as beautiful in colour, more elegant in form, lighter and easier to carry, and as much bigger as she pleases, than the famous ones of Cleopatra and Servilla. In Scotland, as well as in the East, the smooth and perfect shell rarely produces a pearl; the crooked and distorted shell seldom wants one.

Artificial Pearls. There are methods of making artificial pearls, in such manner as to be with difficulty distinguished from the best oriental. The ingredient used for this purpose was long kept a secret; but it is now discovered to be a fine silver-like substance found upon the under side of the scales of the blay or bleak fish. The scales, taken off in the usual manner, are washed and rubbed with fresh parcels of water, and the several liquors suffered to settle; after which the water being poured off, the pearly matter, of the consistence of oil, remains at the bottom, and is called by the French essence d’orient. A little of this is dropped into a hollow bead of bluish glass, and shaken about so as to line the internal surface; after which the cavity is filled up with wax, to give solidity and weight. Pearls made in this manner are distinguishable from the natural only by their having fewer blemishes.

Mother-of- Pearl, the shell, not of the pearl oyster, but of the mytilus margaritiferus. PEARL-Ash, a fixed alkaline salt, prepared chiefly in Germany, Russia, and Poland, by melting the salts out of the ashes of burned wood, and, having reduced them to dryness, evaporating the moisture, and, calcining them for a considerable time in a furnace moderately heated. The goodness of pearl-ashes may be ascertained by a uniform and white appearance; but they are nevertheless subject to a common adulteration, not easily distinguishable by the mere appearance, and which is done by the addition of common salt. Pearl-ashes are much used in the manufacture of glass, and need no preparation, except where very great transparency is required.