Ivory.

Scientific American 5, 21.10.1848

Ivory is the osseous matter of the tusks and teeth of the elephant, the hippopotamus, or morse, &c. The hardest, toughest, whitest, and clearest ivory, has the preference in the market; and the tusks of the sea-horse are considered to afford the best. In these, a rough glassy enamel covers the cortical part, of such hardness, as to strike sparks with steel. The horn of the Narwhal is sometimes ten feet long, and consists of an ivory of the finest description, as hard as that of the elephant, and susceptible of a better polish; but it is not in general so much esteemed as the latter.

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 moist rubbing and exposure may be repeated several times.

For etching ivory, a groung made by the following receipt is to be applied to the polished surface:- Take of pure white wax, and transparent tears of mastic, each one ounce; asphalt, half an ounce. The mastic and asphalt having been separately reduced to fine powder, and the wax being melted in an earthware 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 taffery. If white rosin be substituted for the mastic, a cheaper composition will be obtained, which answers nearly as well; 2 oz. asphalt, 1 oz. rosin, ½ oz. white wax, being good proportions. Callot's etching 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 figure 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 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 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 dilute solution of neutral nitrate of pure silver, with access of light, it will assume a black color, 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 imersed for a longer or shorter time in a solution of indigo (partly saturated with potash), it assumes a blue tint of greater or less intensity.

3. Green Dye. - This is given by dipping blue 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 impregnanting the ivory first with the above tin mordant, and then digesting it with heat in a stained 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 communicated to ivory by steeping it 18 or 24 hours in a strong solution of the neutral chromate of potash, and then plungung it for some time in a boiling hot solutionf of acetate of lead.

5. Red Dye - may be given by imbuing the ivory first with the tin mordant, then plunging it in a bath of Brazil wood, cochineal or a mixture of the two. Lac-dye may be used with still more advantage, to produce a scarlet tiat. If the scarlet ivory be plunged for a little in a solution of potash, it will become cherry red.

6. Violet Dye - is given in the logwood bath to ivory previously mordanted for a short time with a solution of tin. When the bath becomes exhausted, it imparts a lilac hue. Violet ivory is changed to purple-red by steeping it a little while in water containing a new drops of nitro-muriatic acid.

With regard to dyeing ivory, it may in general be observed, that the colors penetrate better before the surface is polished than afterwards. Should any dark spots appear, they may be cleared up by rubbing them with chalk, after which the ivory should be dyed once more to produce a perfect uniformity of shade.

On taking it out of the boiling hot dye bath, it ought to be immediately plunged into cold water, to prevent the change of fissures being caused by the heat.

If the borings and chips of the ivory-turner, called ivory dust, be boiled in water, a kind of fine size is obtained.