Information on Diamond Cutting by Machine in 1921
EVEN IN SUCH A DELICATE OPERATION as the cutting and polishing of diamonds, machinery is now fast supplanting hand-work, and mechanical devices are relied on instead of the operator's eye and judgment.
B. K.Price, who writes on the subject in Abrasive Industry (Cleveland), tells us that America is now the largest diamond-buying country in the world. New York is becoming a great center of the diamond-cutting industry. The diamonds here are first sawed or cleaved into sections, and then cut and polished by the special machinery that has superseded manual operations. Diamond-cutting, Mr. Price tells us. is one of the oldest of the abrasive processes, and yet mechanical methods were not applied to the art until recent years. The trade has been handed down from generation to generation, and the advancement of mechanical equipment in the industry has been slow. The two most important recent developments have been, first, the invention of the diamond saw, and second, a practical mechanical device for cutting diamond facets. He writes;
"Until a half century ago, the cutting of diamonds for sale in this country was carried on almost entirely in Holland and Belgium, and to a slight extent in England. However, since the United States is the largest diamond-buying nation in the world, it is only natural that the cutting industry would be developed here, and its expansion in recent years has been phenomenal. Approximately 90 per cent. of the country's diamond-cutting shops are located in New York, within four city blocks in the heart of the downtown business section. Here also is located the diamond dealing center of the United States, the most unique feature of which is the diamond curb market at the corner of John and Nassau streets.
"As received by the diamond-cutter, the stones usually are octahedral in shape, and the process involved in preparing them for the market consists either in cleaving or sawing them into a workable shape and then cutting each stone round and shaping the facets. There are exceptions, however, in the case of particular stones that lend themselves to cutting into fancy shapes. The uncut diamonds first are inspected carefully to determine weight, flaws and cleavage planes. In the majority of cases the stone is sawed, and in that event it is marked with ink to guide the operator. A certain percentage of diamonds, however, never are sawed or cleaved, going direct to the cutter and polisher.
"The stone is set in a metal container termed a dop with a matrix of lead or plaster. It is located for sawing according to its grain, the machine being provided with suitable adjustments to enable the operator to set the stone at the desired angle. The wheel or so-called saw is phosphor bronze, ranging from 0.0025 to 0.007-inch in thickness and is approximately 4 inches in diameter. The saw is operated at speeds from 2200 to 2400 revolutions per minute, according to the quality of the stone. The sawing process on a one-carat stone takes about a day. Sometimes large stones remain in the machine from a week to a month. In some of the shops in this country 100 of those machines are in operation.
"The phosphor bronze saws are impregnated with a mixture of olive oil and diamond dust which imparts the necessary abrasive qualities. Occasionally as many as six stones, weighing one carat each, can be cut with one saw. Phosphor bronze is used because it makes a rigid saw sufficiently porous to hold the abrasive mixture.
"While the sawing process is used extensively in cutting a rough stone into two or more sections, the cleaving of diamonds is by no means a forgotten art. In fact, a certain amount of cleaving must be carried on in every diamond shop. To cleave a diamond calls for the exercise of extreme skill and rare judgment. The operation consists of cementing the stone in a depression in the end of a wood handle, while another diamond is used to cut a groove at the desired point of cleavage. Then by inserting a cutting tool, which resembles a dull knife, the stone is broken into two sections by a sharp hammer blow."
After the rough stones have been reduced to the desired sizes they are ready for cutting, which is done by rubbing one against another. One is revolved at 1000 to 1200 revolutions a minute while the other, on the end of a handle, is manipulated so that the wear on both stones is approximately equal. From one-half to one hour is consumed in cutting a one-carat diamond.
Source: Literary Digest - December 3, 1921