At the time the manufactured ruby was a novelty it fetched as much as £6 a carat, but as soon as it was discovered that it could easily be differentiated from the natural stone, a collapse took place, and the price fell abruptly to 30s., and eventually to 5s. and even 1s. a carat. The sapphires run slightly higher, from 2s. to 7s. a carat. The prices of the natural stones, which at first had fallen, have now risen to almost their former level. The extreme disparity at present obtaining between the prices of the artificial and the natural ruby renders the fraudulent substitution of the one for the other a great temptation, and it behoves purchasers to beware where and from whom they buy, and to be suspicious of apparently remarkable bargains, especially at places like Colombo and Singapore where tourists abound. It is no secret that some thousands of carats of manufactured rubies are shipped annually to the East. _Caveat emptor._ CHAPTER XV IMITATION STONES The beryl glass mentioned in the previous chapter marks the transition stage between manufactured stones which in all essential characters are identical with those found in nature, and artificial stones which resemble the corresponding natural stone in outward appearance only. In a sense both sorts may be styled artificial, but it would be misleading to confound them under the same appellation. Common paste,[6] which is met with in drapery goods and cheap ornaments in general—hat-pins, buckles, and so forth—is composed of ordinary crown-glass or flint-glass, the refractive indices being about 1·53 and 1·63 respectively. The finest quality, which is used for imitations of brilliants, is called ‘strass.’ It is a dense lead flint-glass of high refraction and strong colour-dispersion, consisting of 38·2 per cent. of silica, 53·3 red lead (oxide of lead), and 7·8 potassium carbonate, with small quantities of soda, alumina, and other substances. How admirable these imitations may be, a study of the windows of a shop devoted to such things will show. Unfortunately the addition of lead, which is necessary for imparting the requisite refraction and ‘fire’ to the strass, renders the stones exceedingly soft. All glass yields to the file, but strass stones are scratched even by ordinary window-glass. If worn in such a way that they are rubbed, they speedily lose the brilliance of their polish, and, moreover, they are susceptible to attack by the sulphurous fumes present in the smoky air of towns, and turn after a time a dirty brown in hue. When coloured stones are to be imitated, small quantities of a suitable metallic oxide are fused with the glass; cobalt gives rise to a royal-blue tint, chromium a ruby red, and manganese a violet. Common paste is not highly refractive enough to give satisfactory results when cut as a brilliant, and the bases are therefore often coated with quicksilver, or, in the