Chap. 76.] METHODS OF TESTING PEECIOUS STONES. 463 



another.^^ Sardonyx, for example, is imitated by cementing 

 together three other precious stones, in such a way that no 

 skill can detect the fraud ; a black stone being used for the 

 purpose, a white stone, and one of a vermilion^- colour, each 

 of them, in its own way, a stone of high repute. Nay, even 

 more than this, there are books in existence, the authors of 

 which I forbear to name,*^ which give instructions how to stain 

 crystal in such a way as to imitate smaragdus and other trans- 

 parent stones, how to make sardonyx of sarda, and other 

 gems in a similar manner. Indeed, there is no kind of fraud 

 practised, by which larger profits are made. 



CHAP. 76. (13.) THE METHODS OF TESTING PRECIOTJS STONES. 



On the contrary, we will make it our business to point out 

 the methods of detecting these false stones, seeing that it is 

 only proper to put luxury even on its guard against fraud. 

 In addition to the particulars which we have already given, 

 when treating of each individual kind of precious stone, it is 

 generally agreed that transparent stones should be tested by 

 a morning light, or even, if necessary, so late as the fourth"^ 

 hour, but never after that hour. The modes of testing^^ stones 

 are numerous : first, by their weight, the genuine stone being 

 the heavier of the two ; next, by their comparative coolness, 

 the genuine stone being cooler than the other to the mouth ; 

 and, next to that, by their substance ; there being blisters per- 

 ceptible in the body of the fictitious stone, as well as a certain 

 roughness on the surface ; filaments, too, an unequal brilliancy, 

 and a brightness that falls short before it reaches the eye. 

 The best^^ mode of testing is to strike off a fragment with 

 an iron saw ; but this is a thing not allowed by the 

 dealers, who equally refuse to let their gems be tested by the 

 file. Dust of Obsian^' stone will not leave a mark upon the 

 surface of a genuine stone : but where the gem is artificial, 



^^ Substituting garnets for rubies, as an illustration. 



^2 '■' Minium." See Chaper 23 of tliis Book. 



83 Lest the deception should be commonly practised. Seneca, Epist. 19, 

 mentions one Democritus, who liad discovered the art of making artificial 

 Emeralds. See further on this subject, Beckmann, Hist. Inv. Vol. I. p. 

 124. Bohn's Edition. ^^ Ten in the morning. 



8= See Chapters 18 and 20. 



86 "We can only guess at the meaning of this passage, as it isacknow- 

 ledgedly corrupt. 



«^ Our Obsidian. See B. xxxvi. c. 67, and Chapter Q5 of this Book. 



