A good remedy against the liability which pearls manifest of losing their brilliancy is to keep them in magnesia. An artificial imitation of pearl is largely made on the Continent, the essential ingredient being guanine, a silvery mucus found on the scales of Lenciscus alburnus, which is incor porated with wax, and may be either bored and strung as pearls, or spread to resemble mother-of pearl. (See also Celluloid, p. 615, for artificial pearl-making).
Coral (Fn., Corail ; GER., Koralle).—There is still great ignorance on many important points relating to the production of coral. The little that is known leads to the belief that its growth is rapid ; that its development is simple ; that it accommodates itself to very varied circumstances ; and that detached fragments from the bunch or principal stem have vitality, and will attach them selves to fixed substances for continuing their development and forming new trunks. But at what age coral attains its largest size ; how long it takes for an exhausted coral bank to recover itself; at what period the eggs are laid ; how the products are disseminated ; at what period the budding takes place, and how long it lasts : these questions, on which rests the progress of the coral fishery, are as yet unsolved.
Coral stem is divisible into two distinct parts : a central axis, hard and brittle, which is the part used in commerce ; and a soft covering or epidermis, which easily yields to the nail when fresh, but is friable when dry.
Coral of various kinds is met with in shops, and sold under the names of" white coral "(Oculina [Madrepora] virginea)," brainstone coral " (Mendrina cerebriformis), coral "(G. Antipathes), and "organ-pipe coral" (Tubipora musica), named from the arrangement of its cylindrical dark-crimson tubes. Occasionally "red coral" is found without any colouring matter. Black coral takes a fine polish, and is fashioned into beads, and month-pieces for cigars. The dull white is not quite so hard, and not polishing well, is sold cheaper. It is often deteriorated by being worm-eaten.
Coral has the hardness and brilliancy of agate ; it polishes like gems, and shines like garnet, with the tints of the ruby. The larger branches are used for carving. Large, perfect, well-shaped beads are by far the most valuable form of coral, and these have greatly increased in estimation of late years. Many of the finest are sent to China, while tons of what may be called " worm-eaten " beads, which would not find favour in Europe, go to India, where they are esteemed.
Much of the coral is wasted in the process of conversion into uniform well-shaped beads, and this, of course, adds greatly to the cost. The manufacturing processes consist of three different operations—cutting, piercing, and rounding ; these are principally executed by the females of the Val du Bisagno, in Italy.
The principal commercial varieties of coral distinguished are :—red, subdivided into deep crimson red, pale-red, and vermilion (rare) ; black ; clear-white ; and dull-white (most common).
The delicate rose or flesh-coloured, which is the most prized, is sold at very high prices, as it is entirely a fancy article. Red coral is sometimes classified into twelve shades, besides white and pink ; sometimes into five commercial grades :—(1) froth of blood ; (2) flower of blood ; (3, 4, 5) blood of first, second, and third qualities.
Coral is valued according to its bulk, colour, soundness, and freedom from defects. Certain rare kinds, of pale tints, are worth twenty times their weight in pure gold. The ornamental applications of coral are very varied.
All corals possess a certain industrial value as sources of lime for building and manurial purposes ; but the red or precious sort (Corallium rubrura) is the only one forming an important article of commerce, and to it the following remarks apply.
The localities affording it are the N.-E. and S. shores of the Mediterranean, the coasts of the chief islands in that sea, and a portion of the E. shore of the Adriatic. It usually lies at 2-10 miles from the Mud, and in water of 30-130 fathoms, finding its most favourable conditions in 80 fathoms. It is said to attain greater perfection in the E. than in the S., and to be rarely found in a W. and never in a N. aspect. It occurs attached to rocks embedded in a muddy sea-bottom, where it flourishes better than in clear or sandy beds.
The headquarters of the Italian coral-fishery are: From the island of Elba to the coast of the mainland by Cecina and Spezia ; the so-called secede corallere grounds in the Bay of Naples ; Nico ; the Sorrent peninsula ; near Nisida and Cape Miseno, E. of the island of Ischia : both coasts of Calabria ; the islands between Sicily and Calabria ; near, Sciacca, and the island of Pantellaria ; the Tizzano ground between Corsica and Sardinia; around Sardinia the grounds of Alghero, Longo Sardo, Bosa, Castelsardo. Isola di S. Pietro, S..Autioco, Maddalena and Caprera, from the Straits of Bonifacio, along the Corsican coast to Cape Corso ; thence into French territory, from the Iles de Hyeres to Cape Couronne ; in the Gulf of Rosas and on the banks of Cape Tarsuela di Mongril, to the limit of the gulf in Catalonia. The Italian coral-fleet in 1869 numbered 200 large and 260 small boats, the crews were a total of 4000, and the yield was 160,000 kilo. of coral, valued at 9,600,000 lire (of 91d.). Since then, the industry has much increased, if the statement be true that during last year (1880) some 500 boats from Torre del Greco alone were on the Sciacca bank, besides an equal number from four other ports. The annual value of the Sardinian coral is esti mated at 60,0001., giving a profit of 13,000/. ; the exports are 200,000-250,000 lb. a year. The fishery lasts from March till October.