IMITATION GEMS

Dominion, Volume 14, Issue 265, 3 August 1921, Page 7

IMITATION GEMS

DIAMOND MAKING SYNTHETIC RUBIES AND SAPPHIRES The "culture” pearls which appear - to have been disturbing Hatton Garden, London, are not by any means the only imitations of precious jewels. Almost all gems have been simulated. With rubies and sapphires, science, indeed, has been very successful. For the manufacture of synthetic rubies, a representative of the London "Observer’ was informed by the manager of a firm of jewellers, a small crystal of silicate of alumina coloured by bi-chromate of potash is rotated at a very high speed whilst kept at a temperature of 1800 degrees centigrade by means of an oxyhydrogen blqwpipe. It is then covered with minute particles of natural ruby, ami eventually with great care and patience a large bead is built up from which rubies can be cut. Artificial sapphires are made'in a similar way. In structure the artificial ruby differ from the natural ruby in several ways. The colouring, for example, runs in a circular form, whereas in the natural stone it is either straight or forms de; finite angles. The little "air bells which are often seen in artificial rubies are perfectly round.- They are never this shape in the natural stone. In real rubies, moreover, there is often wh Is known as "silk,” which runs straight lines across the stone, gntog it » hazy appearance, * hlch ?, eVW seen in that which is made artificially. The emerald and other atones arc> often imitated in “doublets and trl P } * ; In the doublet the surface is a real eton. nn.l the back coloured, glass, U>e two being cemented together with balsam. The triolet has a real stone top am. bottom, P with glass sandwiched between “to 'produce diamonds artificially two tblngs MO necessary, heat and pressure simultaneously applied. There have lem several experiments which hate produced diamonds from the pomt °f ! v cHmrr a success, but commercially an utter faUure, the cost always far ex-, seeding their th- . iron filings One method was to place and! pure sugar charcoal in an LirnJce with a of about Thhndee C. At this heat the iron oi gnn to’vaporise. It was then , into molten lead. This process solidified the outer skin of the tng 7 cooling. The interior expanding as It solidified put it under enormous. pi«sure The iron was eaten nway ny acid and left tome small crystals which were diamonds, but they did not exceed half a. millimetre in diameter. Another method which was tried wa. that of using tho power from the MFalls. A great electric furnace was built up in a bed between two large plates, to which the electrfic connections wore attached. First of all clay X puddled in, then layers alternately of silicious sand, coke, sawdust sugar and salt, the latter as a flux with n centre core of carbon blocks;. These were covered again with the same materials anti finally packed once more with clay, and covered. When the-current was put on it would arc from block to block on tho carbon core and would thus.produce an enormous heat. This was kept up for fl month or more. When the furnace was broken down a thin core of very small diamonds of no marketable value, was found, but a valuable product was discovered, namely carborundum which is next hardest to the diamond, and is used extensively as an abrasive in many industries. . "Japanese pearls,” continued the Observer’s” linfrtrmant, "were ” e '~ fore those which have been cultivated by Mr. Mikimoto. The former process consisted in fastening a small particle.of pearl under the oyster in its shell, the irritation having the effect of causing it to throw over it layer after layer of nacre or spittle. When tho pearl thus formed was cut away from its shell it was about three-parts real pearl on the outer surface, the remainder being mother of pearl. **ln the pe?rl now on tho market, which is also produced by an artificial stimulus, the whole of the surface is real pearl. It has been stated that it is impossible to detect its 'culture. This, however, is not tho case. “Practically DO per cent, of these cultured pearls can be picked out with ease, and the remaining 10 per cent, with difficulty. Some of these pearls are. of course, better than others, but it will not be long before wo are able to detect every one of them as readily as we can reconstructed or synthetic rubies. . "Lapis lazuli is a stone which has been stimulated a great deal, and in more ways than one. The Germans have nut on the market an alabaster imitation. which is coated with a blue substance. This imitation, if scratched with a knife, will show a white mark. "Jasper, which is a real stone, is sometimes stained with blue and passed as lapis, or Swiss lapis, the word lazuli being omitted. Tho market difference between the real stone and the imitation is considerable, for whereas a lapis lazuli necklet will cost anything from -£:>o to .£2OO. a jasper necklet is worth no more than a few pounds. Imitations of a cruder kind are obtained with blue china and blue glass. . “Chinese jade is another stone of which there are imitations on the market. The majority of these stones are of Chinese origin, and I do not think they were made with the intention of deluding the public. The Chinese mandarins, like many European ladies, did not always wear their actual jewels, but imitations of them, and it is these pieces of mandarin chains which one comes across. They can be fairly easily detected bv tho spherical air bells which thev contain. »

“The public, of course, can always protect themselves against imitations, in the first place by dealing only with the best iewellers. and in the second, if n«cessary, bv having a written guarantee of genuineness. Many of the imitations can be defected without the aid of experts at all. Where, for example, glass is used for the purpose of simulation, it can be scratched with a knife or file-. No precious stone, with the exception of tho opal and turquoise, can be so scratched.