Ivory has the same constituents as the teeth of animals, three-fourths being phosphate, with a little carbonate of lime; one-fourth cartilage. See [Bones].
It is extensively employed by miniature painters for their tablets; by turners, in making numberless useful and ornamental objects; by cutlers, for the handles of knives and forks; by comb-makers; as also by philosophical instrument makers, for constructing the scales of thermometers, &c. The ivory of the sea-horse is preferred by dentists for making artificial teeth; that of the East India elephant is better than of the African. When it shows cracks or fissures in its substance, and when a splinter broken off has a dull aspect, it is reckoned of inferior value. Ivory is distinguishable from bone by its peculiar semi-transparent rhombohedral net-work, which may be readily seen in slips of ivory cut transversely.
Ivory is very apt to take a yellow-brown tint by exposure to air. It may be whitened or bleached, by rubbing it first with pounded pumice-stone and water, then placing it moist under a glass shade luted to the sole at the bottom, and exposing it to sunshine. The sunbeams without the shade would be apt to occasion fissures in the ivory. The moist rubbing and exposure may be repeated several times.
For etching ivory, a ground made by the following recipe is to be applied to the polished surface:—Take of pure white wax, and transparent tears of mastick, each one ounce; asphalt, half an ounce. The mastick and asphalt having been separately reduced to fine powder, and the wax being melted in an earthenware vessel over the fire, the mastick is to be first slowly strewed in and dissolved by stirring; and then the asphalt in like manner. This compound is to be poured out into lukewarm water, well kneaded, as it cools, by the hand, into rolls or balls about one inch in diameter. These should be kept wrapped round with taffety. If white rosin be substituted for the mastick, a cheaper composition will be obtained, which answers nearly as well; 2 oz. asphalt, 1 oz. rosin, 1⁄2 oz. white wax; being good proportions. Callot’s etching ground for copper plates, is made by dissolving with heat 4 oz. of mastick in 4 oz. of very fine linseed oil; filtering the varnish through a rag, and bottling it for use.
Either of the two first grounds being applied to the ivory, the figured design is to be traced through it in the usual way, a ledge of wax is to be applied, and the surface is to be then covered with strong sulphuric acid. The effect comes better out with the aid of a little heat; and by replacing the acid, as it becomes dilute by absorption of moisture, with concentrated oil of vitriol. Simple wax may be employed instead of the copperplate engravers’ ground; and strong muriatic acid instead of sulphuric. If an acid solution of silver or gold be used for etching, the design will become purple or black, on exposure to sunshine. The wax may be washed away with oil of turpentine. Acid nitrate of silver affords the easiest means of tracing permanent black lines upon ivory.
Ivory may be dyed by using the following prescriptions:—
1. Black dye.—If the ivory be laid for several hours in a dilute solution of neutral nitrate of pure silver, with access of light, it will assume a black colour, having a slightly green cast. A still finer and deeper black may be obtained by boiling the ivory for some time in a strained decoction of logwood, and then steeping it in a solution of red sulphate or red acetate of iron.
2. Blue dye.—When ivory is kept immersed for a longer or shorter time in a dilute solution of sulphate of indigo (partly saturated with potash), it assumes a blue tint of greater or less intensity.
3. Green dye.—This is given by dipping blued ivory for a little while in solution of nitromuriate of tin, and then in a hot decoction of fustic.
4. Yellow dye—is given by impregnating the ivory first with the above tin mordant, and then digesting it with heat in a strained decoction of fustic. The colour passes into orange, if some brazil wood has been mixed with the fustic. A very fine unchangeable yellow may be communicated to ivory by steeping it 18 or 24 hours in a strong solution of the neutral chromate of potash, and then plunging it for some time in a boiling hot solution of acetate of lead.