DETECTING FAKES.

Manawatu Times, Volume 61, Issue 193, 17 August 1936, Page 10

DETECTING FAKES.

SCIENCE COMES TO AID OF JEWELLERS.

TESTING OF PRECIOUS STONES. Talced and imitation precious stones nave recently become such a nuisance to jewellers that the London Chamber of Commerce has issued a special booklet te'lling how to distinguish the real from the false. So difficult to detect, are some of these imitations, particularly those rnado synthetically by chemical processes, that the diamond, pe'nrl, and precious stone section of the Chamber lias established a laboratory in Hatton Garden specially equipped for testing precious stones.' In addition it has arranged classes for jewellers at which they are taught the best methods of detecting‘imitation stones. “Claims- have been put forward from ’tifri'e to"tirrie,” says- the booklet, “that exact imitations could be made of diamonds, pearls, emeralds, rubies, and sapphires. In recent years these claims have become bolder, and it is now maintained that not even experts can distinguished between the real and .the imitation article. can be considered genuine unless it is entirely produced. by Mature. Any gem produced artificially, however closely it may resemble the real article of Nature, always has certain characteristics by which it can be Identified.”

Diamond Scare. The recent “scare” which arose when it was reported that a new process for producing diamonds had been evolved led the Chamber to go Into the whole question of imitation stones. “Tests show,” they report, “that these so-called ‘synthetic diamonds’ are not composed of diamond materials. In hardness, physical properties, and chemical composition they have nothing in common with genuine diamonds. "Apart from the ‘scare’ in diamonds, the most vexed question in recent years in the trado has been that of cultured pearls. A very old system of the Chinese was to insert in the pearl oysters figures of Buddha and also clay pellets which were then covered with pearl secretion, specimens of which can be seen in the Natural History Museum at South Kensington. "The Japanese improved the method by inserting mother-of-pearl beads which became covered uniformly with pearl secretion. The claim, however, ithat they are real pearls cannot be accepted any more than a gilt or rolled gold article can be accepted as a solid gold article. “It is not disputed that cultured pearls are legitimate articles of commerce, but they cannot be classified or sold as real pearls. As far as the legal side is concerned, it has been decided both in France and America that they must never be sold as real pearls.” The endoscope, which throws a beam of light through the hole drilled in the pearl, and X-ray machines, which are used for undrilled pearls, can distinguish a cultured pearl from a genuine pearl, and are in use at the laboratory. Synthetic rubies and sapphires are the most difficult to detect, because they have the same hardness and physical properties as the natural stones. They are made by fusing together the necessary chemical ingredients under intense heat. Careful examination under a microscope is sometimes necessary before a stone can be' definitely pronounced artificial. At the Hatton Garden laboratory an instrument called a dishroscope has been Installed to test stones of this group. Genuine rubies show two colours when seen through the 1 instrument — purplish red and yellowish red—in the two squares of the machine. Faked stones show the same colour in both squares. This Instrument is also used for testing emeralds. Another simple aid for testing emeralds is a colour filter. When seen through a filter, the genuine emerald appears red, while imitations retain their green colour. Apart from synthetic stones there are other ingenious forms of imitalioc known as “doublets.”

“Doublets.” “Pastes” (glass imitations), states the booklet, “are much softer and have different properties from . the real stones. Thus the only other artificial stones which may occasionally deceive the unwary are certain types of ‘doublet’ which defeat a simple hardness test. More difficult to detect - are the sapphire ‘doublets,’ of which there are three types. In one, two pieces of pale sapphire are cemented together with transparent, material of a deep blue colour; another has a pale sapphire front cemented to an underside of blue glass; while a third has a sapphire back and front and a layer of blue glass between. “Doublets," out of their setting, can be easily detected when viewed on edge immersed in water. Immerslan , in liquid Is also of assistance in deI tecting markings in synthetic stones