SYNTHETIC JEWELS

Greymouth Evening Star, 13 July 1935, Page 10

SYNTHETIC JEWELS

CHALLENGE TO NATURE

From the days of Tut-ankh-apien to the days o£ Diamond Jim Brady it has been a virtually universal custom for wealthy and‘ spectacular mortals to symbolise their mundane gloty. bj decking their exteriors with precious stones. Such stones are nothing more than small lumps of certain rare minerals and from a strictly utilitarian standpoint are quite useless Yet so much artificial value has been put upon them by human vanity that they have been searched for by explorers, fought over by soldiers, laboured upon by artisans, invested in by financiers, and wept for by fair ladies. And also, it must be confessed, no small amount of scientific ingenuity has been expended in trying to make them artificially, • . A precious stone must have certain definite properties aside from its rarity. It must, of course, be beautiful to look upon. It must be very hard, so that it will not become scratched or worn away during longusage. It must refract, or bend, light to a considerable extent, so that it vyill sparkle when cut properly. And it must be able to disperse the various colours of the spectrum, so that it will show a little fire along with its sparkling. Chemically speaking, the average precious stone is not worth very much. The diamond, for example, is nothing more than a pure carbon in a certain crystalised form. Chemically it is ho different from graphite or lampblack. The amethyst is nothing more than a crystal of coloured sand. Rubies and sapphires are virtually identical with the cheap artificial abrasive known as corundrum, owing their colours to traces of impurities. An emerald is nothing more than a beryl of a different colour. Of course, if these gems happened to be as common as sand they would not be entirely useless. -fThe fact that extreme hardness is one of their properties indicates that they would bo used for grinding or cutting other materials. As a matter of fact, the diamond, which is far harder than any -other known substance, has a number of well-known applications along this line. It must be remembered, however, that the diamonds used for this purpose have imperfections which . prevent their use as gems.

Since there is ho little real difference between valuable gems and the previously mentioned cheaper materials. it is to be expected that a lot of work would bo done toward trying to make artificial precious stones. It should be noted that the word artificial does not mean the same as imitation. An imitation gem is one made out of some cheap material, such us glass, while an artificial one is identical with the real thing in composition and appearance* and differs from it only in the fact that it was made through the agency of man rather than of nature.

Imitation jewels have been known for thousands of years. They are made for the most part out of glass coloured suitably for this particular purpose. The glass usually is colcured by certain mineral substances; for example, gold gives a red colour, cobalt oxide a blue, and silver oxide a yellow. Ordinary window or brittle glass is not used, as its optical re-

fraction and dispersion are definitely less than those of natural gems. FIRST ARTIFICIAL DIAMOND.

Lead glass, which is a. glass containing a large amount of lead oxide, can be made to show the correct optical properties, and accordingly is the basis for most of the imitation jewellery. Unfortunately, this lead content also introduces the undesirable property of softness in the glass. Such imitations are quite easily recognised by an expert. Since the diamond is the most expensive of gems, and since it is also chemically identical with such cheap materials as charcoal or coke, especial efforts have been made to reproduce it artificially. Unfortunately, the conversion of charcoal or graphite into diamond is by no means easy. A diamond is more than 50 per cent, more dense than graphite. In other words, the carbon in a diamond is packed into a third less space than it would seem reasonable that the application of a very high pressure would be necessary to change graphite into diamond. This has been tried, but it was found that the pressures produced by the usual industrial methods are insufficient to bring about this change.

About 40 years ago Moissan, the French chemist, who pioneered in the study of chemical reactions at extremely high temperatures, learned that someone had analysed a piece of a meteorite and had found a few tiny diamonds in it. Moissan decided to try to prepare diamonds by subjecting carbon to the same treatment it would receive in a meteor.

Now, meteorites consist largely of iron, and iron possesses a number of interesting properties. For one thing, molten iron will dissolve several per cent of its weight of carbon, and will throw most of this carbon out of solution when it solidifies. Moreover, the presence of this carbon converts the iron into steel. Finally, iron is like type metal or water in that it expands when it changes from a liquid to a solid. Moissan melted up a small batch of iron and dissolved as much charcoal in it as it would hold. He then cooled the molten mass quickly by plunging it into molten lead: after all, hot and cold are relative terms, and he- found that molten lead would cool the iron much more quickly than water would. The mass of iron solidified first on the outside, forming a strong steel jacket. The iron on the inside then solidified, throwing most of the dissolved carbon out of solution. But since the expansion of the iron was checked by the steel shell around it. a tremendous pressure developed, subjecting the carbon to the combined effect ol high temperature and pressure. Then when the iron was dissolved away by acid it was found that most of the carbon had been changed into graphite, but scattered through this graphite mass were a few small diamonds. This was quite a triumph from a standpoint of pure science. But unfortunately its commercial applications were decidedly limited, its most] of the diamonds were too small to] see without, a magnifying glass. The; largest of them was only about l-athh of an inch in diampter. Since that time there have been several attempts to improve upon these results by modifying the procedure, but without any appreciable success. RUBIES AND SAPPHIRES. The production of synthetic rubies and sapphires, however, has been •

made commercially practicable. Both of thege gems consist of crystallised aluminium oxide, along with small amounts of certain minerals to give the colour. The ruby owes its colour to a few per cent of chromium oxide, while the sapphire’s blue is the result of traces of the oxides of iron and titanium. In the commercial manufacture of these stones a fine powder of aluminum oxide and the colouring agent is gradually shaken into the intensely hot flame of hydrogen and oxygen. The molten powder then falls upon a email pedestal of some infusible material, where it gradually builds up a small globule of the desired product. These synthetic stones are identical with the natural ones in both appearance and composition. In fact, they are almost too good. The only way of detecting a ruby’s origin lies in the fact that the natural gems have a number of microscopic flaws that are absent in the artificial ones. During the last dozen years the products of this process have become serious competitors to natural rubies and sapphires. Attempts to prepare artificial eni■eraids have not been so successful, it is possible to prepare the stones, but unfortunately they happen to be of microscopic size. As for various other more common stones, no serious effort has been made to produce them on a commercial scale.

Of great importance in industry is the matter of abrasives. The makers of tool steels are faced with a dilemma like that of the munition makers who simultaneously must keep improving their shellproof armour plate and also their armour-piercing shells. The tool-makers must develop more and more resistant steels, and at the same time find harder abrasives with which to grind tiiis steel.

The naturally occurring abrasives, such as emery, have long since been found unsatisfactory. The high temperatures of the electric furnace, however, have made possible the production of a number of much harder artificial materials. One of the first of these was silicon carbite, or carborundum, which is prepared by the intense heating of sand and coke. Corundum mentioned above, is aluminum oxide that has been melted in an electric furnace and allowed to crystallise. A recent development is that of boron carbide, prepared from boric acid and coke. Next to the diamond it is the hardest substance known.—Thomas M. Beck in the “Chicago Tribune.”