TORTOISESHELL. - The covering of the Testudo imbricata, and on the working of which the reader is referred to vol. 1, pages 126 - 135, is usually polished after one of the following modes: - 1. - Tortoiseshell Handles for razors and penknives, combs, spectacle frames, and many similar works, after they have been sawn out and moulded into form, (see vol. 1, page 130,) are smoothed with a float or single cut file technically known as a quannet, (see vol. 2, page 838,) and then shaved or scraped smooth with a scraper like that used by joiners. Cutlers often use an old razor blade the edge of which has been sharpened at right angles, by placing the blade perpendicularly on the oilstone.
The works are then very sparingly polished on a wheel covered with thick buff leather, such as the bull neck, or sea cow, and fed with calcined Trent sand and oil, (see article on Horn, page 1067,) and they are finished on a similar wheel supplied with rottenstone and oil, occasionally the latter wheel is alone used. Razor handles and some other works are often handed up, or finished with the naked hand and dry rottenstone, and works required to be very nice and flat are more generally treated as follows: - 2. - Flat Works in Tortoiseshell, such as card and needle cases and others that require to be kept flat, are floated and scraped as above, and Mr. W. Vanham before referred to says, that he afterwards successively employs pumice-stone, putty-powder and rottenstone on three different buff sticks, and all generally with water but sometimes with oil, as the treatment varies according to the material inlaid in the tortoiseshell, which is lastly finished with the hand and rottenstone or whiting. When the works have mouldings and sharp edges that would be rounded by the buff stick, the same materials are used on slips of wood filed to the appropriate forms. 3. - Tortoiseshell when turned in the Lathe is usually smoothed with fine glass or emery paper, and finished with rottenstone and oil, on linen or woollen rag. TOUCHSTONE is a compact black basalt or Lydian stone, of a smooth and uniform nature, and is used principally by goldsmiths and jewellers as a ready means of determining the value of gold and silver by the touch, as it is termed - that is, by first rubbing the article under examination upon the stone, its appearance forms some criterion; and, as a further test, a drop of acid, of known strength, is let fall upon it, and its effect upon the metal denotes its value.