AGATE. Some of the uses of Agate in the mechanical and useful arts are described in Vol. i. page 173, and this substance although much harder than Carnelian is cut and polished precisely after the same manner, and which process is fully described under the head Carnelian in this Catalogue.
ALBATA or British Plate of the best kind is treated almost like silver work. In polishing spoons made of the inferior kinds of Albata, the 1st operation, which is called roughing, is done upon bobs (see WHEELS, article 51,) covered with sea-horse hide with a plentiful supply of Trent sand and oil; 2ndly, rottenstone and oil is used; and 3dly, the finishing is done upon bobs with oil and very finely powdered lime, materials that are of the cheapest kind, and require little or no preparation. Albata or German Silver is polished by the mathematical instrument makers the same as Brass. See that article, paragraph 4.
ALUMINA, in a compact or crystalline form is the base of some very hard mineral substances used in the arts, namely, emery, corundum, sapphire and ruby, of which it constitutes from 86 1/2 to 98 per cent.: these are only exceeded in hardness by the diamond. See the table, page 1029.
AMBER after having been filed, may be polished 1st with Trent sand, or scraped Flanders brick on flannel with water; 2ndly, rottenstone with oil on flannel; 3rdly, rottenstone dry on the hand.
Turned works are generally polished first with glass paper, and then with rottenstone and oil.
The lapidary works amber just after the mode described under Alabaster, article 3, but necklaces and other ornaments in amber that are cut into facets, are more usually and better executed by the gold cutters, or those artizans who cut and polish facetted works, and by the same routine as that described in the article 3, under the head Gold.
AMETHYST or violet quartz is cut and polished by the lapidary like Carnelian, which see.
AQUAMARINE, called also Beryl, and Ancient Beryl, is of various shades of pale yellow, green and blue, it was so named from its resemblance to sea water, and is worked like Carnelian.
ASTERIA. See Sapphire.
BERYL, a term that designates amongst lapidaries and virtuosi a very rich deep brown diaphanous carnelian; it is frequently engraved into intaglios, just after the manner of carnelian generally.
BETEL-NUTS, when turned, are in general polished only with fine glass paper, and a few of their own shavings; whiting and water may be used as for Ivory.
BLOODSTONE is a very hard, compact variety of hoematite iron ore, which when reduced to a suitable form, fixed into a handle, and well polished, forms the best description of burnisher for producing a higher lustre on gilt coat-buttons, which is performed in the turning lathe by the Birmingham manufacturers. The gold on china ware is burnished by its means. Burnishers are likewise formed of agate and flint; the former substance is preferred by bookbinders, and the latter for gilding on wood, as picture-frames, etc." - Knight. Bloodstone, the appellation sometimes employed by the lapidary and jeweller, to distinguish a dark green stone usually containing red spots, whence its popular name of bloodstone; it is mineralogically known as the Heliotrope, and is considered as a variety of chalcedony: this stone is worked exactly like Carnelian, but is much harder and takes longer to polish.