186 THE DIAMOND MINES OF SOUTH AFRICA
Loss in Cutting
No
general rule can be stated covering loss which occurs in cutting gems.
The waste depends on the character of the stone, — its perfect natural
form and crystallization, its purity, and the style of the cut adopted.
Perfect octahedrons lose two-fifths of their weight, if cut as
brilliants. Rhombohedrons will lose over half of their weight in taking
the same form, and stones of other shape will lose as much or more. The
following figures will show at what cost of substance some of the
natural gems have been perfected in the process of their cutting: The
Mogul in its rough outer coat weighed originally 780-1/2 carats ; when
cut it weighed only 279 9/16 carats, a loss of nearly
two-thirds. The Regent weighed 410 carats and was reduced to 136-1/2
carats. The weight of the Koh-i-nur was originally 793 carats. It was
first cut unskilfully by Hortensio Borgio to 186-1/2 carats, and a
second cutting reduced it to 102-1/2 carats, — a loss by both processes
of the astonishing amount of 690-1/2 carats, or more than six and a
half times its present weight. The L'Etoile du Sud shrunk from 254-1/2
carats to 124-9/16 carats in the process of cutting.1 The
average loss of South African diamonds by cutting is from one-half to
three-fifths of their gross weight. The 428-1/2 carat diamond found in
De Beers mine lost 200 carats in cutting.
It
has been demonstrated in cutting that diamonds are of different degrees
of hardness and that the same stone may exhibit different degrees on
different faces. The Koh-i-nur is a signal example of this fact. In
cutting the facet near a yellow flaw, the section grew noticeably hard,
until six hours' grinding at a speed of 2400 revolutions a minute
produced only the faintest change. A speed of 3000 revolutions was
necessary to cause any perceptible loss of material on that facet. A
speed of 4000 revolutions a minute is about the average now in vogue at
Amsterdam.2
1 " Famous Diamonds of the World," Streeter, 1882.
2 Description by Messrs. Veder and Rozelaar, dated 6th March, 1902.
