IMITATIONS AND TESTS	71
	chemical properties and pressure, cannot, of course, maintain these continuously for " ages," therefore the chemist must manufacture the jewels in such manner that he may soon see the results of his labours, and though real diamonds may be made, and with comparative ease, from boron in the amorphous or pure state along with aluminium, fused in a crucible at a high temperature, these diamonds are but microscopic, nor can a number of them be fused, or in any other way converted into a large single stone, so that imitation stones, to be of any service must be made of a good clear glass. The glass for this purpose is usually composed of 53.70 per cent, of red lead, 38-48 per cent, of pure quartz in fine powder, pre­ferably water-ground, and 7.82 per cent, of carbonate of potash, the whole coloured when necessary with metallic oxides of a similar nature to the constituents of the natural stones imitated. But for colourless diamonds, the glass requires no such addition to tint it. From the formula given is made the material known as "strass," or " paste," and stones made of it are mostly exhibited under and amongst brilliant artificial lights. The mere fact that they are sold cheaply is prima facie proof that the stones are glass, for it is evident that a diamond, the commercial value of which might be £50 or more, cannot be purchased for a few shillings and be genuine. So long as this is understood and the stone is sold for the few shil­lings, no harm is done : but to offer it as a genuine stone and at the price of a genuine stone, would amount to fraud, and be punishable accordingly. Some of these "paste," or " white stones," as they are called in the trade, are cut and polished exactly like a diamond, and