260 SYSTEMATIC DESCRIPTION OF PRECIOUS STOiNES 



6. IMITATION AND COUNTERFEITING. 



Attempts have often been made by unprincipled dealers to pass off* stones of little value 

 or worthless imitations as genuine diamonds. The gems of inferior value most frequently 

 used for this purpose are colourless topaz, zircon rendered colourless by heating, white 

 sapphire, spinel, beryl, tourmaline, phenakite, and even rock-crystal and other minerals. 

 In all these stones, however, the beautiful play of prismatic colours so characteristic of the 

 diamond is far less marked, as is also, except, perhaps, in the case of colourless zircon, 

 the peculiarly high lustre of the diamond. No one in the least degree familiar 

 with the appearance of the diamond would for a moment confuse it with any of the 

 stones just mentioned. Among the physical characters by which the diamond may be 

 distinguished from other colourless gems are hardness, specific gravity, and refraction of 

 light, the spinel alone of the minerals mentioned above being singly refracting like the 

 diamond. The diamond is much less frequently confused with coloured than with 

 colourless gems. 



In absence of colour, in transparency, lustre, and play of prismatic colours, some kinds, 

 of glass, especially strass, resemble the diamond with astonishing closeness. This material] 

 is, therefore, largely used in the manufacture of imitation diamonds, and so closely does the- 

 appearance of a piece of freshly-cut strass simulate that of a genuine diamond that it is. 

 possible even for an expert to be deceived. The genuineness, or otherwise, of such a stone 

 can, however, be easily a,nd conclusively proved by a simple test of the hardness with a steell 

 point or file. 



The construction of so-called doublets for the purpose of deception is by no means-, 

 infrequent. In such cases the upper portion of the brilliant is of diamond, while the lower- 

 is of glass or of some colourless stone such as white sapphire. The device by which the 

 yellow tinge of a diamond is temporarily concealed, namely, by applying a thin coating of 

 some blue substance, has been already referred to. The play of prismatic colours,, 

 characteristic of the diamond, is imitated with a certain amount of success by painting 

 the under side of the counterfeit stone. Arbicles of this description, known as irises, have 

 found a ready sale, without any attempt at passing them off' for anything other than what, 

 they are. 



