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 the 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 brilliolette, 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 the 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, but when and where is still a mystery. And it is thought that the famous twelve Mazarins were also cut after this shape.
The star pattern, which was invented by Caire, is but little used at the present time.
CHAPTER XIII.
TESTING OF THE DIAMOND, ETC.
The testing of the diamond is generally an easy matter to the expert, but the merchant and the amateur are often unable to decide quickly concerning the character of a gem that may be offered to them. The learned Abbé Haüy was often called in consultation upon matters of this kind, and even appeared in court as an expert of diamonds. Fortunately, the methods of ascertaining the diamond beyond a doubt are now so easy and numerous that few attempts are made like those of the last century, when white topazes and zircons were sold or substituted for diamonds.
We may be permitted to say that the first and surest test of the gem is that of hardness, and that the diamond scratches all other substances with ease. The application of this test is not always made with facility, but a little practice with a rough crystal of diamond will soon enable the experimenter to perform it satisfactorily. In performing the test for hardness for all gems it is well to be provided with a fine English file, and splinters of quartz, topaz, and sapphire. The file, adroitly applied, will detect the character of gems below the quartz in hardness, and the splinters above mentioned will determine all others but the diamond.
In applying these tests, it is well to touch the middle of a facet, if the gem be polished, and remember that the edges of many of the gems are very brittle. The diamond, for instance, although it is so very hard when its surface is directly tested, yet its thin edges, when cut into a gem, are broken down with the greatest ease; therefore the test of hardness should be applied to the polished face of the stone.
But when the stone has been polished and set in such a manner that the test of hardness cannot be easily applied, then the easiest method of distinguishing its character is to expose it to the rays of artificial light and observe their effects. If the stone, when placed at a certain distance from the candle, flashes out the prismatic hues in a marked manner, then the observer may safely conclude that the object is either a diamond or one of the artificial gems known as strass. To distinguish them by means of the eye alone will be a difficult task, for both possess very high refractive powers and exhibit remarkable displays of the prismatic hues; but the application of a fragment of diamond, sapphire, or topaz to the object will at once make known its character, and even the test of the steel file will betray the softness of the glass.
The transparent zircons closely approach the diamond in brilliancy, and are among the rarest of gems; in fact, a fine specimen of perfect purity would be worth more to the amateur than a diamond of equal weight. The pure yellow are declared by King to be among the rarest and most beautiful of gems on account of their remarkable brilliancy and lustre. He also states that they are seldom found above two karats in weight.
The white zircon, which resembles the diamond so closely, is always minute and rarely above one karat in size. All that are known in commerce come from Matura, in Ceylon, and are sometimes called Matura diamonds. In times past they were in great demand for incrustation work of watches and jewelry, for when cut in the form of roses and set upon brilliant foil they could not be easily detected by the eye from the diamond. At the present day they are seldom seen in commerce, but whether from scarcity, or from an improvement in the ideas of honor in the jewellers, we are unable to state. We know, however, that they are still mined by the natives of Ceylon, and are used in Asia for ornamental purposes. The white spinel is sometimes mistaken for the adamas; but its inferiority in hardness and its want of the prismatic hues render its detection easy. The white topaz, when of two or three karats weight, resembles the diamond in the rough very closely, especially when in the modified or globular forms of crystallization. The degree of specific gravity is exactly the same; but the test of hardness and the want of the prismatic display serve to dispel all doubts as to its nature. Neither of these gems, nor the white sapphire, has that peculiar sharp flash of the diamond which is known as the adamantine eclat. It has been stated by Hoppè that some of the Brazilian diamonds do not exhibit any more play of color when cut than rock crystal; but we have no doubt but that the writer is in error, and has probably been deceived by some of the white spinels or topazes which are sometimes found in the diamond mines of Brazil and are of great brilliancy.