Popular Science Monthly/Volume 8/December 1875/Diamond-Cutting
THE process of diamond-cutting is a very simple matter to those acquainted with the nature of the gem. To cut the facets, two stones are cemented on two sticks, and rubbed against each other until a facet is cut; then the position of one of the stones is changed, and another flat surface is cut. The process is thus continued until the gem is faceted all over. After the facets are cut, and a definite form given to the stone, the diamond is placed in the hands of the polisher, who fastens it in solder, and then holds it against a small steel disk revolving horizontally with a speed of 1,500 to 3,000 times a minute. This disk is moistened with oil mixed with diamond-powder, and one facet is polished at a time. Diamond-cutting proper is a rapid operation, but the polishing is slow and tedious. One cutter can generally furnish sufficient work for four or five polishers.
There are a number of forms adopted by the lapidaries for these gems, but the two principal ones are the brilliant and the rose. The former pattern, first practised in Europe in the seventeenth century, is by far the best adapted for calling forth the powers of the gem. The other form is of unknown antiquity, and has long been in use among the Hindoos. It affords the largest beams of light for the weight, but it lacks greatly in colored reflections when compared with the brilliant.
For the perfection of the rainbow-play of hues, it is essential that the facets of the superior and inferior parts of the stone should correspond in exact proportions, and stand at fixed distances, so as to multiply the reflections and refractions, and produce the colors of the prismatic spectrum. All limpid and white gems must be cut according to this rule, but with colored stones the case is different, for here perfection of color is to be attained, and brilliancy is a secondary consideration. Hence, a fine ruby or sapphire may be decidedly thin, and yet be a gem of great beauty and value.
|Fig. 1.—Stewart Diamond. Rough South African Crystal, weight, 288-3/8 carats.||Fig. 2.—Star of the South. Rough weight, 254-1/2 carats.|
The process of rifting diamonds by splitting them in their cleavage-planes was known long ago to the Hindoos, but was forgotten to modern lapidaries till revived by Wollaston not many years ago. By this means masses of the crystal may be removed to escape a flaw or remove a spot. Some diamonds of the spheroidal form are deficient
|Fig. 3.—Mattam Diamond. Borneo. Rough weight, 367 carats.||Fig. 4.—The Koh-i-noor before Recutting.|
in cleavage-planes, and are quite impracticable for cutting; others have a concentric arrangement of the planes of cleavage, as though crystallization radiated from the centre, and it is very difficult to polish them. The Hindoos avail themselves of the natural cleavage of the gem, and form table diamonds by adroitly striking along one of the planes with a sharp-edged tool, thereby separating the layers, as slate is rifted by the miner. This operation, which appears so simple, really requires considerable skill, and much of that acquired instinct or tact which is best exhibited by our Western Indians, who chip, with marvelous rapidity and certainty, a glass-bottle into symmetrical arrow-heads.
The workman at a glance ascertains the direction of the laminæ, and with another diamond cuts a notch at the point where he would begin operations. In this notch he places the edge of his blunt steel knife, and, by tapping the back of it with a light iron rod, he splits the diamond with perfect ease. In reducing the natural diamond to a regular form, much of its substance is lost, and sometimes as much as one-half the weight of the stone. The amount of loss, however, depends
|Fig. 5.—The Koh-i-noor after Recutting. Weight, 1021⁄2 carats.||Fig. 6.—The Regent. Weight, 136 carats.|
greatly on the natural form of the crystal. Perfect octahedrons lose but one-fifth of their weight when fashioned into brilliants, but rhombohedrons lose over one-third on taking the same form. The following figures will give some notion of the loss:
|The Mogul weighed in the rough||7801||carats|
|Reduced in cutting to||2799||"|
|The Regent weighed 410 carats; reduced to||13614||"|
|The Koh-i-noor weighed 1861 carats; reduced to||1021||"|
|The Star of the South weighed 2541 carats; reduced to||1244||"|
The process of cutting diamonds of large size is always attended with risk, and is necessarily a costly operation. The Regent cost for cutting $25,000, and occupied two years' time. The Star of the South occupied only ninety days, and the Koh-i-noor only thirty-eight working-days. This great feat in diamond-cutting was performed by the ablest of the Dutch lapidaries, with the aid of steam-power. The cost of cutting is said to have been $40,000—reduced, however, to some extent by the sale of the fragments.
The process of diamond-cutting has within a few years been established in the United States. Mr. Henry D. Morse, a jeweler of Boston, conceived the idea of constructing a machine for cutting and polishing the gem. While engaged in perfecting his appliances,
|Fig. 7.—Proper Size of Brilliant Diamond, 100 carats, according to Jeffries's Scale.||Fig. 8.—Form of the Brilliant-Cut|
chance threw in his way an itinerant vender of porcelain, who had once been employed as a workman in the diamond ateliers of Amsterdam. The sight of the rough gems and the apparatus recalled to the mind of the Jew the scenes of his youth, and awakened a desire to resume his former occupation, and he offered to do the work of a diamond-cutter. But, as the process was carefully considered, it was discovered that the Jew could only cut the facets of the diamond, and the art of the subsequent polishing he did not understand. It seemed strange that an artisan who possessed the rare ability to tell at a glance how large a gem the stone would cut, how to avoid internal imperfections, and how to take advantage of the cleavage-planes, could not polish the facets after he had cut them. But such was the fact, for the two processes of cutting and polishing are widely different, and require separate instruction. However, the deficiency was soon supplied by an acquaintance who was induced to leave Holland and act as polisher in the American diamond adventure. The establishment was now complete, but the business was at first confined to recutting and repolishing gems that had been damaged by long use or accident. The inventive genius of Mr. Morse made several important changes in the machinery required by the lapidary, and displaced the rude and cumbersome apparatus of the old system. At first but two or three men were employed, but, after the discovery of the South African diamond-mines, the rough gems soon furnished abundant material, and now several men and boys are constantly employed, with the aid of steam-power.
In consequence of the success of the South African diamonds, and the abundant supply of the stones, another atelier has been established in New York, under the direction of Mr. J. Hermann. A large amount of capital is said to be invested in this adventure, and employment is given to forty or more workmen, all Israelites, with the aid of steam-power. The establishment already boasts of having cut a fine crystal from South Africa, weighing eighty carats.
|Fig. 9.—Form of the Rose-Cut.||Fig. 10.—Form of the Table-Cut.|
The process of cutting the diamond is divided by the Jews into several distinct branches, and workmen are educated to perform one part but not another. Thus the cleaving, the cutting, and the polishing, have special operators, who become expert in performing well the parts assigned to them, without attempting the others. This course has undoubtedly produced skillful workmen, but we see no reason why all the parts may not be perfectly acquired by an intelligent mechanic. The art of cleavage, however, requires tact, and ought to include some knowledge of mineralogy. For the particulars of the art of diamond-cutting, we will refer our readers to the interesting works of Jeffries, Mawe, and Barbot; still we briefly mention here some of the forms adopted for the diamond, and how they are produced.
|Fig. 11.—The Star of the South. Weight, 1241⁄4 carats.||Fig. 12.—The Great Mogul. Weight, 2799 carats.|
The table and the rose patterns were the first regular forms adopted by the lapidaries. The first was simply the top of the stone ground flat, with a corresponding flat bottom of less area, with its four upper and lower sides parallel to each other. As the light passed through the stone without much refraction, the beauty of the mineral was not developed by this pattern. It has been stated that the rose-shape was invented in Paris, under the auspices of Cardinal Mazarin; but Tavernier describes the diamonds of Aurungzebe as being of the rose-cut. Therefore, we must give a more ancient date to the pattern than Mazarin's day. The form of the rose-cut is simply that of a hemisphere, covered with small facets. Its flattened base is therefore admirably adapted for incrustation-work, and the foil on which it is usually set serves as a reflector for the entering rays of light. The rose-pattern has several names, indicating the number of facets. If it has but twelve or less facets, it is called an Antwerp rose; if but eighteen or twenty, it is a semi-Holland; and a Holland rose, if it bears twenty-four facets. At the present time these gems are not in much demand, unless for incrustation-work, for which they are superior, both in effect and in adaptability to the surface of the object to be ornamented.
The form which appears to exhibit the splendors of the gem to the best advantage, is that known as the brilliant, and is rightly named from its effects. It was discovered in Italy, in the latter part of the seventeenth century, by Peruzzi, of Venice, which city was then one of the chief gem-marts of the world. The conclusions which led to the adoption of this shape were derived from experiments upon colored stones. This form of the brilliant is that of the ancient deep
table modified by receiving thirty-two facets above and twenty-four below its girdle. The great relative depth of the gem, aided by the numerous facets of the sides, appears to increase the natural refractive power of the stone by confining, as it were, the rays of light inside of it. Another pattern, called the brillolette, shows the beautiful qualities of the gem to great advantage. It is formed like two rose-diamonds joined together at the base; or may be flattened and elongated like an almond, and faceted all over with small facets. This is the form of the Sancy, and should have been given to the Koh-i-noor and the Star of the South. The Austrian yellow diamond is of this pattern, and was probably cut in India. And it is thought that the famous twelve Mazarin diamonds were also cut after this pattern. The star-pattern, which was invented by Cane, is but little used at the present time.
- From a work on "The Diamond," in the press of D. Appleton & Co.