IVORY was the name formerly given to the main substance of the teeth of all animals, but it is now restricted to that modification of dentine or tooth-substance which in trans verse sections shows lines of different colors running in circular arcs, and forming by their decussation minute lozenge-shaped spaces. By this character, which is presented by every portion of any transverse section of an elephant's tusk, true ivory may be dis tinguished from every other kind of tooth-substance, and from every counterfeit, whether derived from tooth or bone. Although no other teeth, except those of the elephant, present this characteristic, many other animals, such as the walrus, narwhal, hippopotamus, etc., possess teeth, horns, or tusks, which, from their large size and from their density-, can be used for the same purposes in the arts as those for which true ivory is employed. The ivory of the tusks of the African elephant is held in the high est estimation by the manufacturer, on account of its greater density and whiteness. The tusks are of all sizes, from a few ounces in weight to more than 170 lbs. each. Holtzapffel states that he has seen fossil tusks from the banks of the rivers of northern Siberia which weighed 186 lbs. each.' There arc various chemical processes by which it may be dyed of various colors, as black, blue, green, yellow, red, and violet.
Ivory articles can be made flexible and semi-transparent by immersion in a solution of phosphoric acid of sp. gr. 1.130, till they become translucent. They are then to be taken out, washed with water, and dried with a soft cloth, when they are found to be as flexible as leather. They harden on exposure to dry air, but resume their pliancy when immersed in hot water.
Much important information on the subject of ivory generally will be found in Holtzapffel's Mechanical Manipulation.
The tusks of the elephant have from very early periods constituted an important article of trade, in consequence of their.great beauty as a material for ornamental mann
factnres, and even works in fine art. Ivory is frequently mentioned in the Old Testa ment. With the Greeks it became a 'most important material, and by the hands of the sculptor Phidias a statue was produced of the Olympian Jupiter, of such marvelous beauty and imposing majesty that it was considered a misfortune to die without having seen it. By the Romans, who were supplied from Africa, it was also extensively used and by them its use was diffused over the whole of Europe. The art of working in ivory* doubtless had its origin in India, where it has always been a much valued mate rial, and formerly supplied indirectly much of the ivory sent to Europe. The value of ivory is in proportion to the size and soundness of the teeth. Below the weight of 5 lbs. they are called scrivelloes, and are of the least value, rarely reaching 5 shillings per pound; but double that price has been given for teeth of unusually large size. The quantity imported into Great Britain from all parts rather exceeds 500 tons per annum, the value of which is about £400,000.
The so-called ivory obtained from the hippopotamus is in especial favor with dentists for making false teeth, on account of its pure white color and freedom from grain. The fossil ivory, which is found in considerable quantity in Siberia and the arctic regions, is uncommonly hard and brittle; it is also whiter, and wants its waxy softness. At pres ent the demand for ivory is rapidly increasing, owing to the great taste and skill of some of the artists who work in this material, and as the supply increases but very slowly it is likely to become very dear. The beautiful art of ivory-carving has recently made very extraordinary prOgress in Europe, as has been shown by works in ivory sent to the various international exhibitions; some single specimens have had a value of £500.