Precious Stones. 221 



known to the ancients ; it is ascribed to Louis von Berg-hem in 

 1456, The Dutch are now the great diamond cutters for the 

 world, the chief establishments being at Amsterdam, where the 

 largest mills, those of Mr. Coster, employ, as Mr. Emanuel 

 tells us, five hundred to six hundred workmen. " To this firm 

 was entrusted the cutting of the Koh-i-noor." 



Mr. Emanuel observes, " the general form of the rough 

 diamond is of two pyramids joined at the base : if a diamond 

 is not naturally of this form, it must be made so by art.''-' To 

 cut diamonds, two stones are fixed with cement to the top of 

 two sticks, and they are rubbed together till a facet is pro- 

 duced. " It must be understood that by this operation only 

 the general outline of the form is made. A stone which would 

 have, when quite completed, fifty- eight facets, including the 

 table and culet, receives in cutting only eighteen, eight of 

 which are the surfaces of an octohedron, or double pyramid, 

 and are formed by taking away eight edges or angles of these 

 eiofht surfaces, one for the whole table and one for the culet." 

 The "table" is the flat face at the top of a brilliant; the 

 " culet" is the small face terminating the pyramid into which the 

 back of the brilliant is worked. In the rose form of cutting 

 there is no "table." The " diamond polishing" on a steel disc, 

 with diamond powder, gives the remaining facets required for 

 the perfect form, and leaves the surface brilliantly smooth. 



In Mr. Emanuel's book will be found a series of diagrams 

 representing the different patterns into which diamonds are 

 cut, and he also gives views of the most famous diamonds in 

 the world. 



In the case of the diamond we have an instance of a very 

 common material having its particles so arranged as to confer 

 upon it very remarkable properties not exhibited by the same 

 substance in other conditions. The ruby, the sapphire, the 

 oriental topaz, the oriental emerald, and some other gems, are 

 composed of a material as common as carbon — namely, 

 alumina, the earthy oxide of aluminium, a metal now in 

 frequent use, and the basis of all kinds of clay. In Dana's 

 Mineralogy these gems are treated as minerals composed of 

 uncombined alumina, but this is not absolutely true. Mr. 

 Emanuel gives an analysis of a ruby, or red sapphire, which 

 represents it as containing — ■ 



Alumina 98'5 



Oxide of Iron 1 • 



Lime .5 



100- 

 And it is probable that these minute quantities of extraneous 



