Ivory, the osseous substance which composes the tusk of the elephant, and which is a peculiar modification of dentine. In commerce it is customary to include in the term the tusks of the hippopotamus, the walrus, the narwhal, and some other animals; but according to Owen and other high authorities it can only be strictly applied to the peculiar reticulated modification in the elephant's tusk, although this is analogous to the substance (dentine) which forms the main part of all teeth. The appearance given by a cross section of any portion of an elephant's tusk, of circular lines intersecting each other so as to form lozenge-shaped figures with curved boundaries, distinguishes true ivory from all other bony substances, and from all other tooth substances, whether dentine or not. The principal supplies of ivory are derived from the W. and E. coasts of Africa, the Cape of Good Hope, Ceylon, India, and the countries eastward of the straits of Malacca. The best comes from Africa, and is of a finer texture and less liable to turn yellow than that brought from India. Prof. Owen says: "The African elephant, as is well known, is a distinct species from the Asiatic one; and some of the Asiatic elephants of the larger islands of the Indian archipelago, as those of Sumatra, if not specifically distinct from the elephants of continental Asia, form at all events a strongly marked variety;" and he remarks that in the Asiatic elephants tusks of a size which gives them the value of ivory in commerce are peculiar to the males, while in the African elephants both males and females afford good-sized tusks, although the males have the largest.
The best tusks are nearly straight, and in section nearly circular. One of the largest has been found to measure 8 1/4 in. on its longer and 7 in. on its shorter diameter. They are hollow for about half their length, and a line is traced from the termination of the cavity to the tip of the tusk, which marks in the solid ivory the former extension of the cavity. Upon the outside they are coated with a rind one tenth to one fifth of an inch thick, the color of which in the African varieties may be one of numerous transparent tints of orange, brown, or almost black, and in the Asiatic an opaque fawn or stone color. It conceals the quality of the ivory within, which may be partially exposed at the worn tip, but is finally ascertained only on the introduction of the saw by which the tusk is cut up for use. Even in the interior it is often found to be of variable character, opaque patches appearing in the transparent quality, and the white being sometimes marked in rings alternately light and dark colored. In the larger teeth the grain is often coarse in the outer portion, and becomes fine within; and some varieties are of chalky consistency like bone, and present dark brown spots.
The qualities are so variable, that when exact matches are required of several articles it is important to cut them from the same tusk. The chemical composition of ivory is said to differ considerably in the animals of different countries; but this probably depends upon the age of the animal and the part of the tusk from which the specimen is taken, although the kind of food will exercise an influence. The following analysis, taken from the Dictionnaire uni-versel, may be assumed as its average composition: animal matter, dried, 24.00; water, 11.15; phosphate of lime, 64.00; carbonate of lime, 0.10. By very long exposure under favoring circumstances the animal matter becomes dissipated, rendering the texture brittle. This was the condition of some ancient ivory carvings found by Layard in the ruins of Nineveh. To restore their tenacity Prof. Owen recommended boiling them in a solution of gelatine. The experiment proved perfectly successful, and the ivory thus regained its original strength and solidity. A remarkable source of ivory, which has long supplied the Russian markets, is the tusks of fossil mammoths found in the banks of the rivers of northern Siberia. This fossil ivory is of similar quality to that of living animals, and some of the tusks are of immense size.
Holtzapffel says he has seen tusks which were 10 ft. long and weighed 186 lbs. They were solid from their tips to within 6 in. of the larger end, and the ivory was of fine grain and sound texture. - The uses of ivory are very numerous. It is exquisitely smooth in working, altogether devoid of the harsh meagre character of bone, and is in all respects the most suitable material for ornamental turning, as it is capable of receiving the most delicate lines and cutting. The artists of Greece and Rome carved from the tusks of the elephant statues and various works of art, among which those of Phidias are especially famous. The size of some of the statues has led to the opinion that the ancients obtained larger tusks than those of modern times, or that they had a method of softening and flattening out the material, or built it up in plates around a central core. (See Quatre-mere de Quincy's Le Jupiter olympien, ou l'art de la sculpture antique, Paris, 1815.) Ivory was a favorite material for sculpture also in the middle ages, and many beautiful specimens then executed are preserved in museums and private collections. Dieppe in Normandy has been for two centuries the chief seat of this branch of art in modern times.
The Chinese possess extraordinary skill in working ivory, carving out of a solid block a number of hollow balls one within another, all curiously ornamented with various devices. Their chessmen are unequalled in ingenious workmanship. Ivory is largely used for the handles of knives, and for the keys of pianofortes and other musical instruments. Its fine texture and smooth surface recommend it for plates for miniatures; and it is used for a great variety of toys, and of mathematical and other instruments. For drawing scales the material is not found so suitable as box or lance wood, for its dimensions change as it absorbs and gives out atmospheric moisture. Billiard balls are liable to the same difficulty; and as the shrinkage or expansion is greater in the direction of the width of the tusks than in that of their length, the two diameters of the balls are sometimes found to differ materially after they have been made a short time. For this reason they are sometimes roughly shaped and then kept for months in the room in which they are to be used, to acquire the form due to its usual condition as to moisture, when they are finished.
Veneers are cut out of the blocks either in straight longitudinal slips, or, by the method first practised by the Russians upon cylindrical blocks of wood, in a spiral sheet, as if this were unrolled from the cylinder submitted to the operation. In the London exhibition of 1851 a veneer of this kind was exhibited in the United States department, a foot wide and 40 ft. long. In Paris they have been cut in strips of 30 by 150 in.; and a pianoforte has been entirely covered with this material. Ivory may be made flexible by immersion in a solution of phosphoric acid of specific gravity 1.13 till it becomes translucent. It hardens on exposure to dry air, but assumes its flexibility when placed in hot water. - Ivory may be dyed black by soaking it in a solution of nitrate of silver and exposing it to the sunlight, or better by boiling for some time in a decoction of logwood and then steeping in a solution of red sulphate or red acetate of iron; blue by immersion in a solution of sulphate of indigo containing potash; green by dipping the blued ivory in a solution of nitro-muriate of tin, and then in a hot decoction of fustic; yellow by first soaking the ivory in a mordant of nitro-muriate of tin and then in a hot decoction of fustic, or better by steeping it for 24 hours in a solution of neutral chromate of potash, and then immersing it in a boiling hot solution of acetate of lead; red by first saturating it with the tin mordant, and then immersing it in a decoction of Brazil wood or cochineal, or a mixture of both.
Lac dye will produce a scarlet, and this immersed in a solution of potash will become a cherry red. Violet is produced by mordanting with tin and then treating with a decoction of logwood; if this is placed a short time in a weak solution of nitro-muriatic acid, it will be changed to a beautiful purple red. Ivory may also be dyed with any of the aniline colors. - The imports of ivory, hippopotamus teeth, and narwhal teeth into Great Britain from 1861 to 1871 varied from 9,290 cwt. to 14,599 cwt. a year. - Various substitutes for ivory have been introduced. The best known is that called vegetable ivory, an albuminous substance formed from a milky fluid in the fruit of a species of palm common in Peru and New Granada, the phytelepkas macrocarpa. It corresponds to the meat of the cocoanut, the fruit of another species of palm. When the nuts are perfectly ripe and dry, the kernels are hard like ivory and very white. It answers very well for many small articles instead of the genuine ivory, but is more liable to tarnish, and does not wear so well when exposed to friction. The French preparation known as Pinson's artificial ivory is a compound of gelatine and alumina. Slabs or tablets of gelatine or glue are immersed for some time in a solution of alumina in acetic or sulphuric acid.
The alumina separates and becomes incorporated with the glue, and the plates are then removed, dried, and finally polished. Another preparation of artificial ivory is made by working together bone or ivory dust with an equal portion of albumen or gelatine to form a paste, and then rolling this into sheets, and hardening them by drying. Sulphate of barytes finely powdered is used to advantage with one half its quantity of albumen. Tablets thus prepared are used in photography to receive positive pictures. - Ivory Black, prepared by calcining the shavings and dust of ivory, is ground and levigated on a porphyry slab to produce the beautiful velvety material which is the chief ingredient of the ink used in copperplate printing. (See Bone Black.)