IVORY, is the tusk or tooth of defence of the male elephant. It is an interme diate substance, between bone and horn, not capable of being softened by nor so hard and brittle as bone. Sometimes it is an enormous size, weighing nearly 200 lbs. It is of a yellowish, brownish, and sometimes a dark brown color on the outside; internally white, hollow towards the root, and so far as was inserted into the jaw, of a blackish brown color.
It is used for making ornamental uten sils, mathematical instruments, eases, boxes, balls, combs, knife-handles, dice, and toys.
Guillot obtained from 100 parts of ivory, 24 gelatine, 64 phosphate of lime, and 0.1 carbonate of lime.
Ivory is restored in color, by covering it with quick-lime and pouring vinegar on this. After 24 hours rub it with alum powder. The best ivory comes from Ceylon.
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 shads luted to the sole at the bottom, and ex posing it to sunshine. The sunbeams without the shade would be apt to occa sion 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 mastic, each one ounce and asphalt, half an ounce. The mastic and asphalt having been separately reduced to fine powder, and the wax being melted in an earthenware vessel over the fire, the mastic 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 resin be substituted for the mastic, a cheaper composition will be obtained, which answers nearly as well ; 2 oz. asphalt, 1 oz. resin, 1 oz. white wax, being good proportions. Callot's etch ing ground for copper plates, is made by dissolving with heat 4 oz. of mastic 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 copper plate engraver's 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 exposnre to sunshine. The wax may be washed away with oil of tur pentine. Acid nitrate of silver affords the easiest means of tracing permanent black lines upon ivory.
Ivory may he dyed by using the follow ing 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 color, hav ing 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 im mersed for a longer or shorter time in a dilute solution of sulphate of indigo (part ly 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 nitro-muriate of tin, and then in a hot decoction of fustic.
4. Yellow dye is given by impregnating the ivory first with the above tin mor dant, and then digesting it with heat in a strained decoction of fustic. The color passes into orange, if some Brazil wood has been mixed with the fustic. A very fine unchangeable yellow may be com municated 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.