Leisure hours among the gems

by Augustus C. Hamlin

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 at fixed distances, so as to multiply the reflections and refractions, and produce the colors of the prismatic spectrum. Therefore the perfect cutting of the diamond is a mathematical problem, governed by rigid laws.

All limpid and white gems must be cut according to this rule, but in case of colored stones the case is far different; for perfection of color is to be attained, and brilliancy is a secondary thought. Therefore a fine ruby or sapphire may be decidedly thin in form, and yet be a gem of great beauty and value. It is very rare we obtain the full perfection of brilliancy and color in the colored gems; for generally the depth of the finest hues prevents a display of the refractive powers of the stone.

The process of rifting diamonds by splitting them in their cleavage planes was known long ago to the Hindoos; but, strange to say, it was forgotten by modern lapidaries until 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, and yet preserve material that may be utilized, and which would have been lost by the process of grinding away the exterior.

Some diamonds of the spheroidal form are deficient in cleavage planes, and are quite impracticable for cutting; and the fact of the impossibility of polishing them is sufficient proof of their peculiar origin, and that their form is not due to aqueous action.

Others, known as bort, seem to be of concentric arrangement, as though crystallization radiated from the centre; and it is very difficult to polish them. The Hindoos avail themselves of this natural cleavage, and form table diamonds by adroitly striking along one of the planes of the stone with a sharp-edged tool, thereby separating the layers of the gem as the slate is rifted by the miner.

The operation, which seems 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 marvellous rapidity and certainty, a glass bottle into symmetrical arrow-heads. This method of reducing diamonds by cleavage was early known to the Hindoos, and is mentioned by Tavernier in an unmistakable manner in his published travels.

The process of reduction by this means is very rapidly accomplished by the skilful workman. At a glance he ascertains the direction of the laminæ, which remind one of the layers of the onion, and then cuts a small notch with another diamond in the place he selects. In this minute rift he places the edge of his blunt steel knife, and, tapping the back of it with a light iron rod, the diamond is split with perfect ease. By this process flaws and imperfections in the external layers of the stone are removed without delay. In reducing the natural diamond to a regular form much of its substance is lost, and sometimes as much as one half of the weight of the stone. This loss, however, depends greatly upon the natural form of the crystal. The perfect octahedrons lose but one fifth of their weight when transformed into the shape of the brilliant; but the rhombohedrons lose over one third in taking the same form.

The following will give the reader an idea of the losses of the rough stones when converted into fine gems. However, it must be remembered that these great stones are generally of irregular shape and are rarely of fine crystalline forms. The Mogul weighed in the rough 780¹⁄₂ karats, but was reduced in cutting to 279⁹⁄₁₆ karats. The Regent weighed 410 karats, reduced to 136¹⁴⁄₁₆ karats. The Koh-i-noor weighed 186¹⁄₂ karats, reduced to 102¹⁄₂. L’Etoile du Sud, 254¹⁄₂ karats, reduced to 124⁴⁄₁₆.

The process of cutting diamonds of large size is always attended with risk, and is necessarily a costly operation. The Regent cost in cutting $25,000, and occupied two years’ time. The Star of the South, which was cut by Coster, occupied but 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 Holland lapidaries, with the aid of steam power. Although the time expended was less than forty days, yet the cost of cutting is said to have been $40,000, which sum was lessened by the sale of the rifted fragments.

The Oriental lapidaries, destitute of mechanical appliances of any considerable aid, consumed years in cutting some of the paragons of India. This condition of affairs will explain the reason why the Armenian lapidaries asked the immense sum of $80,000 to cut the slab of diamond weighing 130 karats, which was captured by the Sultan of Persia at Coocha, in 1832.