1038 IVORY 



latitude. Some of the ivory of commerce is, or used to be, derived from the tusks of 

 this extinct species.' 



The ivory of the tusks of the African elephant is most esteemed by the manufac- 

 turer for its density and whiteness. 



The outside of the tusk of the elephant is covered by the cortical part, 'which is 

 softer and less compact than the interior substance, with the exception of the brown 

 plate that sometimes lines the interior cavity. The hardest, toughest, whitest, and 

 most translucent ivory has the preference in the market ; for many purposes the horn 

 of the narwhal being considered the best. The horn of the narwhal is sometimes 10 

 feet long. 



The ivory of the hippopotamus is preferred by dentists ; it is much harder than 

 that of the elephant, its colour is a purer white, and it is almost free from grain. 

 The teeth of the walrus, sometimes called the sea-cow, which hang perpendicu- 

 larly from the upper jaw, are also used for the same purpose. The masticating 

 teeth of some of the large animals are occasionally used as ivory; those of tho 

 spermaceti whale are of a flattened oval section, and resemble ivory in section, but 

 they are dark coloured towards tho centre, and surrounded by an oval band of white 

 ivory. 



Ivory has been used for ornamental works from the earliest periods. Phidias is 

 stated to have been famous for his works made in ivory combined with gold, and 

 described as the Torentic Art. The ivory statues of the ancients appear to have been 

 formed upon centres, or cores of wood covered with plates of ivory. 



In our clays ivory has been extensively employed by the miniature painter ; it is 

 used by the turner in the manufacture of numberless useful and ornamental articles ; 

 the cutler makes his best knife-handles from it ; and the philosophical-instrument 

 maker constructs his scales from this material. 



When ivory 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 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 

 1 oz. ; asphalt, ^ oz. 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 1 inch in diameter. These should 

 be kept wrapped round with taffety. If white resin be substituted for the mastic, 

 cheaper composition will be obtained, which answers nearly as well ; 2 oz. asphalt, 

 1 oz. resin, oz. white wax, being good proportions. Callot's etching ground is made 

 by dissolving with heat 4 oz. of mastic in 4 oz. of very fine linseed oil ; filtering tho 

 varnish through a rag, and bottling it for use. 



Either of these 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 bo then covered with strong sulphuric acid. Tho effect comes bettor out with 

 the aid of a little heat ; and by replacing tho 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 bo used for etching, the design will become 

 purple or black on exposure to sunshine. The wax may be washed away oil of tur- 

 pentine. 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 tho 

 ivory for some time in a strained decoction of logwood, and then steeping it in a solu- 

 tion 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. 



