Ivory requires a similar drying, or seasoning, to that recommended for wood; as when the pieces cut out of the tooth are too suddenly exposed to hot dry air, they crack and warp nearly after the same manner as wood, and the risk is the greater the larger the pieces; and on this account ornaments turned out of ivory or wood, especially those composed of many parts, should not be placed upon those chimney-pieces which, from their size, are so close to the fire as to become heated thereby in any sensible manner.

Notwithstanding the difference between the component parts of wood and ivory, and that the latter does not absorb water in any material degree, it is subject to all the changes of size and figure experienced by the woods, and in one respect it exceeds them, as ivory alters in length as well as width, whereas from the former change wood is comparatively free.*

The change however is very much less in the direction of the length than the width; this is particularly experienced in billiard-balls, which soon exhibit a difference in the two diameters, if the air of the apartment in which they are used, differ materially from that in which the ivory had been previously kept. The balls are usually roughly turned to the sphere, for some months before they are used, to allow the material to become thoroughly dry before being turned truly spherical; and in some of the clubs they even take the precaution of keeping the rough balls in their own billiard-room for a period, to expose them to the identical atmosphere in which they will be used.

* See foot note, p. 47. The Tithe Commissioners there referred to, refuse to sanction ivory drawing scales at all, as although they may appear to be correct;it the time of observation, they find them subject to a considerable variation from atmospheric influence. See their Tapers.

Ivory agrees likewise with wood, in shrinking unequally upon the radius and tangent when cutout of quarterings,as explained by the fig. 14, p. 49; on this account, billiard balls are always made out of teeth scarcely larger than themselves, which sued teeth arc called * ball teeth," and procure an advanced price.

It may be asked what means there arc of bleaching ivory which has become discoloured; the author regrets to add that he is unacquainted with any of value. It is recommended in various popular works to scrub the ivory with Trent sand and water, and similar gritty materials; but these would only produce a sensible effect, by the removal of the external surface of the material, which would be fatal to objects delicately carved by hand or with revolving cutting instruments applied to the lathe.

Perhaps it may be truly advanced that ivory suffers the least change of colour when it is exposed to the light, and closely covered with a glass shade. It assumes its most nearly white condition when the oil with which it is naturally combined is recently evaporated; and it is the custom in some thin works, such as the keys of piano-fortes, to hasten this period, by placing them for a few hours in an oven heated in a very moderate degree, although the more immediate object is to cause the pieces to shrink before they are glued upon the wooden bodies of the keys. Some persons boil the transparent ivory in pearl-ash and water to whiten it; this appears to act by the superficial extraction of the oily matter as in bone, although it is very much better not to resort to the practice, which is principally employed to render that ivory which is partly opaque and partly transparent, of more nearly uniform appearance.

It is imagined by some that ivory may be softened so as to admit of being moulded like horn or tortoiseshell, its diffrent analysis contradicts this expectation; thick pieces suffer no change in boiling water, thin pieces become a little more flexible, and thin shavings give off their jelly, which substance is furnished the sketches of the figures and the annexed description.

"In the accompanying drawing is represented the nose of a lathe with an egg chucked ready for cutting. Fig 56, is the section of a chuck for holding the eggs to prepare them for the chuck represented in fig. 57.

"Fig. 56, is what is generally termed a spring chuck, and is made by rolling stout paper thoroughly moistened with glue, upon a metal or hard-wood cylinder, the surface of which has been greased to prevent the paper adhering to it, and upon which it must remain until perfectly dry; when it may be removed, and cut or turned in the lathe as occasion may require."

Figs. 56.

Preparation Of Ivory Etc Part 4 10040

"This sort of chuck is very light, easily made, and well adapted for the brittle material it is intended to hold. Before fixing the egg in it, the inner surface should be rubbed with some adhesive substance, (common diachylon answers exceedingly well;) when this is done, the egg should be carefully placed in the chuck, the lathe being slowly kept in motion by one hand, whilst with the other the operator must adjust its position, until he observes that it runs perfectly true: then with a sharp-pointed tool he must mark the center, and drill a hole sufficiently large for the wire in the chuck, fig. 57, to pass freely through."

"When this is done, the egg must be reversed, and the same operation repeated on the opposite end; its contents must then be removed by blowing carefully through it; it is now ready for cutting, for which purpose it must be fixed in the chuck shown in fig. 57, which is made as follows:"

"A, is a chuck of box or other hard wood, having a recess turned in it at a, b, into which is fitted a piece of cork, as a soft substance for the egg to rest against. B, is a small cup of wood, with a piece of cork fitted into it, serving the same purpose as that in A. A piece of brass, d, is to be firmly screwed into the chuck A, and into that a steel wire, screwed on the outer end; on this a small brass nut, c, is fitted to work freely in a recess in the piece B; when the egg is threaded on the wire through the holes which have been previously made in it, this nut is to be gradually tightened up until it presses the cup, B, against the egg, sufficiently to hold it steady and firm enough to resist the action of a finely-pointed graver used to cut it."

Mr. Kittoe adds that the tool requires to be held very lightly as a little undue violence would crush the shell; neither should the latter be pinched unnecessarily tight in the chuck, as other-wise when the point of the tool divides the shell, the two parts might spring together and be destroyed by the pressure.

It requires some delicacy of hand to attach the rings to the edges of the shell to constitute the fitting; the foot and top ornaments are fixed by very fine ivory screws, the heads of which are inserted within the shell.*

In the next chapter I have to proceed to the materials obtained from the Mineral Kingdom.

* Mr. Kittoe has done me the favour to give me a very elegant example of this fragile manufacture, one rather different from those to which his mind is professionally directed in his study as an engineer, in the works of Messrs. Maudslay, Son and Field He informs me, the shells, when soiled with the fingers, are the most safely cleaned with a solution of citric acid, and that even the eggs of the sparrow may be successfully treated, as above.