Tortoiseshell comes next under consideration. "The animal which produces this beautiful substance, is a marine tortoise, called the Testudo imbricata, or hawk's-bill turtle. Its Latin name is derived from the mode in which the scales on its back are placed, over-lapping one another like the tiles on the roof of a house. In the circumstance it seems to differ from almost all others of its genus." *
* A patent has been taken out by the Messrs. Deakins for making knife-handles, door-knobs, large rings, etc., of horn, by an ingenious combination of moulding and dovetailing; the material from its greasy nature being less adapted to the cementing or soldering process than tortoiseshell.
"On referring to French authorities," says Mr. Aikin, "I find it stated that horn, steeped for a week in a liquor, the active ingredient of which is caustic fixed alkali, become so soft that it may be easily moulded into any required shape. Horn shavings subjected to the same process become semi-gelatinous, and may be pressed in a mould in the form of snuff-boxes and other articles. Horn, however, so treated becomes hard and very brittle, probably in consequence of its laminated structure being obliterated by the joint action of the alkali and strong pressure." - Trans, of the Society of Arts, Vol. LII., page 340.
† Idem, 341.
The usual size of the full-grown animal is about a yard long and three quarters of a yard wide; its covering consists of thirteen principal plates, five down the center of the back, and four on each side, and in a tortoise of the above size, the largest, or main-plates, weigh about nine ounces, and measure about thirteen by eight inches, and one quarter of an inch thick at the central parts; but they are thinned away at the edges where they overlap, owing to the deposition of the substance of the shell in annual layers, each extending beyond the previous one. Very rarely, the shells are three-eighths thick and proportionately heavy. Others are very thin and appear to consist of only one single layer; this is supposed to occur when the animal loses a plate by accident,or that it is stripped and thrown back again into the sea whilst alive; such shells are usually very light coloured and are called "yellow belly." There are also twenty-five small pieces of shell which envelope the edge of the animal, but these can only be applied to very small purposes.
Some of the tortoiseshell is of very dark brown tints running into black, and interspersed with light gold-coloured dashes and marks; these are considered the best; others are lighter, even to pale red-browns, yellow, and white; the last are not valued, the yellow arc used for covering the works of musical snuff-boxes, † and the light red and brown shells are manufactured into ladies' combs, for exportation to Spain, where they obtain double the price of those made of the darker coloured tortoiseshell. The shell of the turtle is also used, but it has not the trans-parent character of the foregoing; the colours are lighter, less beautifully marked, and it is little valued.‡
* Trans. Soc. of Arts, Vo1.LII.. p. 343.
† Some musical boxes are covered with horn or the belly shells of the turtle.
‡ A tortoiseshell merchant of considerable experience informs me that he considers the following the qualities of the different varieties. Manilla, fine and large; Singapore, nearly as good; West Indian, large and heavy, but red; Honduras, better coloured, darker, but with huge dark red spots; Calcutta, dark, heavy, and of bad colour; Bombay shell, the worst and very scabby, from the attachment of barnacles, limpets, etc. There is also the Loggerhead tortoiseshell, which is almost useless, and the Yellow Belly, which plates are very thin and yellow.
Of the Turtle shell, that from Colombina is best, fine and dark; Jamaica, light coloured red and very inferior; East Indian, of middling quality and but seldom met with. The small fishes art called chicknes, and their markings are diminutival powerful screw at the end opposite to the joint; the mould, dies, and horn, are dipped into boiling water for a few minutes, and then screwed as fast as possible immediately on removal from the same, and in about twenty minutes the work is ready for finishing; some handles are made of two pieces joined together.* "Horn is easily dyed by boiling it in infusions of various coloured ingredients, as we see in the horn lanterns made in China. In Europe it is chiefly coloured of a rich red-brown, to imitate tortoiseshell, for combs and inlaid-work. The usual mode of effecting this is to mix together pearl-ash, quicklime, and litharge, with a sufficient quantity of water and a little pounded dragon's-blood, and boil them together for half an hour. The compound is then to be applied hot on the parts that are required to be coloured, and is to remain on the surface till the colour has struck; on those parts where a deeper tinge is required, the composition is to be applied a second time. This process is nearly the same as that employed for giving a brown or black colour to white hair; and depends on the combination of the sulphur, (which is an essential ingredient in albumen,) with the lead dissolved in the alkali, and thus introduced into the substance of the horn." † The horn which is naturally black is less brittle than that which is so stained.
The treatment of tortoiseshell is essentially the same as that of horn, but on account of its very much greater expense, it is economised so far as possible. Before the shells are worked they are often dipped in boiling water to temper them; three or four minutes commonly suffice, but they require a longer period when they are either thicker or more brittle than usual: excess of boiling spoils the colours of the shells, renders them darker, and covers the outside with an opaque white film. Others, flatten and temper the shells with hot irons, such as are used by laundresses; the shell is continually dipped in cold water to prevent its being scorched; but as a general rule the less tortoiseshell is subjected to heat, or to being pulled about, the better, as from its apparent "want of grain" or fibre, it becomes in consequence very brittle.