* See Mr. Rogers' Comb-cutting Machine, Trans. Soc. Arts, Vol. 49, part 2, pp. 150 - 8: since remodelled and improved by Mr. Kelly.
The construction of tortoiseshell boxes requires a copper, with a fire-place beneath the same; a trough with cold water; and the all-important parts, a press and moulds. The former may be compared to the ordinary coining press, or to a strong rectangular frame, usually of wrought iron, with a screw in the center of the upper cross-piece; the base of the press is fitted into a square recess in the center of a bench, fixed so firmly to the floor or wall, as to resist the efforts of two or three men at the end of a lever five or six feet long, whose entire force is sometimes required in tightening the mould. For the convenience of transferring the heavy press, from the hole in the beneh to the hot or cold water, a crane, the center of which is squally distant from the three, is added to the establishment.*
The mould required for a round box consists of a thick wrought-iron ring a a, fig. 39, turned interiorly to the diameter of the box, it stands loosely upon a plate b; it is accurately fitted with several pieces commonly of brass, as c the bottom die, d the top die for a plain box, e a plain block for flat plates, and f a die engraved with any particular device to be impressed upon the work.
* This amusement, described from an English workshop, (Mr. Vauham's,) is toe respects more convenient than the apparatus described in the Manuel du
Tourneur In the Encyclopedia Metropolitana, part Mechanics, article 428, plate xxxiv, is described a press for horn and tortoiscshell, by Holtzapffel and Co., in which the press, crane, and boiler are combined; the cast-iron pedestal contains water and a fire place beneath, and the press is lowered into the water by racks and pinions; as the screw of the press has a multiplying power, the force of one individual suffices and the machine does not require to be fixed to the floor of the apartment.
In the Manuel du Tourneur the methods of making four different kinds of boxes are minutely given. Thus in the "Boites a feuilles," the best kind, in which the cover and bottom part are each made out of a single leaf of shell, the circular pieces are to be cut out of the shell as much larger than the size of the box, as the vertical height in addition to the diameter; so that a box of three inches diameter and one inch deep, would require pieces of four and five inches respectively for the cover and bottom.
The round plate of shell is first placed centrally over the edge of the ring, as in fig. 39; it is slightly squeezed with the small round edged block g, and the entire press is then lowered into the boiling water; in one quarter, or half an hour, it is transferred to the bench, and g, is pressed entirely down, which bends the shell into the shape of a saucer, as at fig. 40, without cutting or injuring the tortoiseshell, after which the press is cooled in the water-trough. The same processes are repeated with the die d, which has a rebate turned away to the thickness of the shell, and perfects the angle of the box to the section fig. 41, ready for completion in the lathe; it is however safer to perform each of these processes at twice, with two boilings.
When the shell is insufficiently thick, two pieces are joined together, and should they from the nature of the shell be of irregular thickness, the thick and thin parts respectively are placed in contact; for such cases the dies c e, of a larger mould are used. The piece d, is adapted to boxes of various depths, or to the tops or bottoms respectively, by slipping loose rings upon it to contract the length of its smaller part.
When the box is required to have a device, an engraved die f, is substituted in place of c. The same tools arc also used for horn boxes, and for the embossed wooden boxes, but but latter process is mostly performed in the dry way, the warmth being supplied by heated plates, put above and below the two parts of the mould which arc then compressed, and the whole is allowed to cool in the air.
The Manuel describes the construction of inferior boxes, "Tabatieres de morceaux," in which small pieces of tortoiseshell with bevelled edges are carefully fitted together with the file and arranged along the bottom and up the sides of the mould; or else they are first pressed into a flat plate, and made into a box as a separate process, but the joints, from the manner in which they are made, can scarcely ever escape observation.
The "Boites de tres-petits morceaux" are made of still smaller fragments, which arc often cemented on a thin leaf of shell to ensure their better union; and lastly, the "Bodes de drogues" arc made of the fine dust and filings, which are passed through a sieve, and treated in other respects much in the same manner as the foregoing, but these boxes are quite opaque and brittle; a thin hoop of good tortoiseshell is sometimes inserted in the mould, to form the rebate of the box, which alone is then transparent; at other times, the shavings are mixed with mineral colouring matters, to imitate granite, lapis-lazuli, and other stones, arts that are scarcely at all practiced in this country.*
After the lapse of ten days or a fortnight, it sometimes happens the box shows a tendency to recover its primary form, that of a flat plate, and from being cylindrical on the edge, it becomes in a slight degree conical and larger without. After being again returned to the mould, boiled and pressed, its figure is in general permanent.
This disposition is turned to useful account in restoring the fitting of a box that may have become loose, as by dipping the lower part, or the rebate, into warm water, it will expand and fill out the lid, but it requires care that it be not overdone.