244 



SYSTEMATIC DESCRIPTION OF PRECIOUS STONES 



Fig. 45. Directions of least hard 

 ness on the facets of a brilliant. 



unnecessarily prolonged. When, for example, the table of a brilliant is to be developed 

 upon an octahedron, the grinding disc should move from centre to centre of two opposite 

 octahedral faces ; if allowed to move from edge to edge, the facet can only be developed 

 with the greatest difficulty, for in this direction the hardness of the diamond is much greater 



than in the other. The directions of least resistance to 

 grinding on each of the facets of a brilliant are indicated in 

 Fig. 45 by arrows. The large four-sided facets above and 

 below and to the right and left of the table, are the faces of 

 the octahedron. 



We have thus seen that the three operations in the 

 process of diamond-cutting are entrusted to as many classes 

 of skilled workmen, namely cleavers, bruters, and grinders 

 or polishers. 



The order in which the facets of a brilliant are ground 

 has also a certain importance. Starting from the octahedral 

 ground-form, the table and culet are in every case first 

 developed. The correct proportions of a brilliant are 

 attained by grinding away five-ninths of the upper half for the table, and one-ninth of the 

 lower half of the stone for the culet, the upper portion of a perfect brilliant being 

 one-third, and the lower being two-thirds of the whole thickness of the stone from table 

 to culet. 



Some rough stones are of such a shape that they cannot be cut into the usual brilliant 

 form, but are given an oval or triangular outline ; in this case, the method of procedure 



described above requires a slight modification, as also when 

 the stone is to be cut as a rose or in some form other than 

 the brilliant. In the latter cases the cleavage of the stone 

 does not play so important a part, but otherwise the mode of 

 procedui'e is much the same. 



In past times the diamond-cutting industry has centred 

 now round this town, now round that. The important 

 invention ascribed to Ludwig van Berquen was made in 1476 

 at Bruges; in the fifteenth and sixteenth centuries, however, 

 most of the work was done in Antwerp, where the workers of 

 L. van Berquen had settled. Later on Amsterdam became 

 the centre of the industry, and through many vicissitudes this 

 city has retained its supremacy up to the present day. In 

 Amsterdam there are now seventy diamond-cutting establish- 

 ments, large and small, fitted up with all the modern technical appliances, and using steam 

 as the motive-power. The industry gives employment tr> more than 12,000 people, all of 

 whom are Jews ; in one establishment alone there are 450 grinding machines and 1000 

 employees, and in the whole of Amsterdam there are said to be a total of about 7000 

 grinding machines (skaifs) at work. Amsterdam, however, no longer monopolises the 

 industry, for skilful cutters are now to be found in Antwerp, Ghent, Paris, St. Claude in the 

 French Jura, London, and specially in Germany, more particularly at Hanau ; diamond- 

 cutting works are also to be found at Berlin and at Oberstein on the Nahe, a town which 

 has long been well known as the centre for the working of agate and other varieties of 

 quartz. In America the diamond-cutting industry has been introduced at Boston. But 

 Amsterdam still holds the lead, and the largest and most valuable stones are always 



Fig. 46. First stage in the de- 

 velopment of a brilliant from an 

 octahedron, showing the position 

 of the table and culet. 



