This term has been applied to a crystalline form of boron prepared by heating boraeic acid - or, what is still better, amorphous borun - with aluminium in a crucible. The name is not a very happy one, as it has been applied to several other articles, and the term "boron" would be much better. Crystallized boron, or adamantine, has not yet come into use in the arts; but from the fact that it is not very difficult to prepare, its peculiar properties may lead to some useful applications.
Wagner gives the following details in regard to its preparation; and as they are not very complicated or delicate, it forms a fine field for amateur experiment: 100 parts of anhydrous boraeic acid are mixed with 60 parts of sodium in a small iron crucible heated to a red heat. To this mixture 40 or 50 parts of common salt are added, and the crucible luted down. As soon as the reaction is finished, the mass - consisting of amorphous boron with boraeic acid, borax, and common salt intermingled - is stirred into water acidified with hydrochloric acid. The boron is filtered out, washed with a weak solution of hydrochloric acid, and placed upon a porous stone to dry, at the ordinary temperature. From this amorphous boron the crystalline boron, or adamantine, is prepared, as follows: - A small crucible is filled with amorphous boron, in the center of which a small bar of aluminium, weighing 4 to 6 grammes, is placed. The crucible is submitted to a temperature sufficient to melt nickel for l 1/2 to 2 hours. After cooling, the aluminium will be found covered with beautiful crystals of boron. The diamond boron is easily separated from the graphitoid. The crystals vary in color from a scarcely perceptible honey-yellow to deep garnet red: sometimes they are so deeply colored, probably by amorphous boron, that they appear black. In luster and refracting power they are nearly equal to the diamond. Their specific gravity is 2 63. They are extremely hard, - always sufficiently so to scratch corundum, or even the ruby, with facility; and some crystals are nearly as hard as the diamond itself. The hardest are obtained by repeatedly exposing aluminium to the action of boric anhydride at a temperature high enough to cause the anhydride to volatilize very quickly.
From the character of boron it would seem eminently fitted for many purposes in the arts. For cutting-tools for very hard substances, for jewels for timepieces, etc., and for ornamental jewelry, it seems specially valuable. Its luster, hardness, and wide range of color, would seem to give it peculiar value for artificial gems.