lastly, take them out and dry them in a warm place, when they will turn yellow.
Ivory is etched or engraved by covering it with an etching ground or wax, and employing oil of vitriol as the etching fluid.
Ivory is rendered flexible by immersion in a solution of pure phosphoric acid (sp. gr. 1·13), until it loses, or partially loses, its opacity, when it is washed in clean cold soft water, and dried. In this state it is as flexible as leather, but gradually hardens by exposure to dry air. Immersion in hot water, however, restores its softness and pliancy. According to Dr Ure, the necks of some descriptions of INFANTS’ FEEDING BOTTLES are thus made.
Ivory is whitened or bleached by rubbing it with finely powdered pumice-stone and water, and exposing it to the sun whilst still moist, under a glass shade, to prevent desiccation and the occurrence of fissures; observing to repeat the process until a proper effect is produced. Ivory may also be bleached by immersion for a short time in water holding a little sulphurous acid, chloride of lime, or chlorine, in solution; or by exposure in the moist state to the fumes of burning sulphur, largely diluted with air. Cloez recommends the ivory or bones to be immersed in turpentine and exposed for three or four days to sunlight. The object to be bleached should be kept an eighth or a fourth of an inch above the bottom of the bath by means of zinc supports. For the preparation of ivory intended for miniature painting Mr Ernest Spon in his useful work, ‘Workshop Receipts,’ says: “The bleaching of ivory may be more expeditiously performed by placing the ivory before a good fire, which will dispel the wavy lines if they are not very strongly marked, that frequently destroy the uniformity of surface.”
Ivory may be gilded by immersing it in a fresh solution of proto-sulphate of iron, and afterwards in solution of chloride of gold.
Ivory is wrought, turned, and fashioned in a similar manner and with similar tools to those used for bone and soft brass.
Obs. Bone for ornamental purposes is treated in a similar way to ivory, but less carefully, owing to its inferior value. The bones of living animals may be dyed by mixing madder with their food. The bones of young pigeons may thus be tinged of a rose colour in 24 hours, and of a deep scarlet in 3 or 4 days; but the bones of adult animals take fully a fortnight to acquire a rose colour. The bones nearest the heart become tinged the soonest. In the same way logwood and extract of logwood will tinge the bones of young pigeons purple. (Gibson.)
1. Ivory, Artificial. Let a paste be made of isinglass, egg-shell in very fine powder, and brandy. Give it the desired colour, and pour it while warm into oiled moulds. Leave the paste in the moulds until it becomes hard.
2. (L’Union Pharmaceutique.) Two parts of caoutchouc are dissolved in 36 parts of
chloroform, and the solution is saturated with pure gaseous ammonia. The chloroform is then distilled off at a temperature of 85° C. The residue is mixed with phosphate of lime or carbonate of zinc, pressed into moulds and dried. When phosphate of lime is used the product possesses to a considerable degree the nature and composition of ivory.