Leisure hours among the gems

by Augustus C. Hamlin

The green variety is probably the rarest of all the forms of sapphire, and finely tinted stones are very seldom seen. They are generally of a faint sea-green tinge, and resemble beryls in their hues. But when they do occur of grass-green color, they form magnificent gems and far exceed the true emerald in lustre and brilliancy. We very much doubt, however, if they ever approach the emerald in its exquisite shade of green. We have examined many green stones from the Ceylon gem mines, and with one exception have found them to be green spinels, zircons, and tourmalines of various intensities of shade. The one undoubted specimen referred to was of an impure hue. The celebrated Romè de L’Isle possessed two beautiful crystals of green sapphire. When they display the sea-green hue or the mountain-blue of the beryl, they are then called Oriental aqua-marines, but fine stones of this description are not common. We have seen some small but very beautifully tinted gems of this class from the gold fields of Montana. Barbot speaks with ecstasy of two green sapphires from Matura in Ceylon, and which far exceeded any other gem in their velvety color, limpidity, and brilliancy. It is possible that these two gems may have been zircons, as these stones abound in Matura, and are of the most vivid lustre when perfect. But stones of fine green hues of this mineral are exceedingly rare. We have also seen a specimen of transparent corundum from Siam which was dichroite, blue and green one way, and entirely green the other. It called to mind that found at Expailly in France, by the naturalist Fanjas, and which appeared of an almost emerald green when viewed in one direction, or of a most beautiful blue when the axis of vision was changed.

The name girasole is applied to those gems that exhibit a peculiar radiance when exposed to the sunbeams. This curious play of light is seen in the transparent and translucent stones, but especially in the translucent. When the gem which possesses this quality is cut in the boss form it shows a glimmering light brighter at one part than at another, owing to a peculiar internal refraction. The effect is very beautiful when the gem is of fine color, and the bright spot moves mysteriously over a more sombre ground as the stone is turned in various directions. The sapphire rarely shows this property to the same perfection exhibited by one of the varieties of opal. We have seen two specimens from the North Carolina corundum mines, which would have been very superior gems if they had not been traversed in all directions by numerous cleavage planes. They were quite an inch in diameter, of a nodular form, and had been deposited in a ledge of ripidolite.

One of the most remarkable varieties of the sapphire is known as the asteria, which was so named by Pliny from the fact of its displaying diverging rays of light. This phenomenon is only seen in stones of semi-opacity or inferior clearness, and the star-like rays are so arranged as to be inclined to each other at an angle of 60 degrees. These stones may be of various colors,—blue, red, or gray,—yet the rays of the star are always white or faintly tinged, and stream forth in beautiful contrast to a ground of delicate blue or decided red. The stars appear the most distinctly to view when the polished gem is exposed to direct sunlight or a small bright flame. This mysterious play is seen in but few of the gems, and the sapphire exhibits it in its greatest perfection. It is indeed a curious thing to see a six-rayed star with long silken beams of light suddenly appear to view as the gem is turned to the light, and as quickly disappear as the focus is changed. No wonder the ancients believed the appearance due to supernatural powers. The microscope, however, has disclosed to the moderns the cause of the asterism. This instrument reveals multitudes of minute crystals within the stone, arranged in three different but equal angles. To obtain the stellate appearance in perfection, then, the stone must be cut and polished in cabochon or dome-like form. The apex of the gem is then in a direct plane to these angles, being perpendicular to the axis of the primitive form of the crystal, and therefore the rays of light are reflected from the sides of these multitudinous crystals producing the asterism.

As we have said before, some other minerals exhibit this phenomenon at times. We find it in rare specimens of quartz and in some of the mica group. In some rare fragments of quartz from Siberia the stellate appearance is seen in extraordinary perfection. The six-rayed star is not only seen by refracted light, but is even visible by transmitted light. Sometimes these stones also exhibit reflections of red and blue as the direction of the stone is changed, thus combining the girasole and asteria in the same gem. Lancon relates that M. Desmaret possessed a little plate of this variety of quartz, of so great beauty and perfection as to refuse 25,000 francs for it. There is in the Museum of the Jardin des Plantes a remarkable diamond asteria; and there are also in this collection and in the cabinet of the École des Mines some superb blue and red sapphire asterias.

The pure white sapphires are not often found. When well cut they exhibit a vivid eclat, and are sometimes mistaken for diamonds; but they are easily detected by the expert, since they do not possess even three fourths of the degree of brilliancy of the diamond, nor the prismatic play of color. Some of the faint-colored stones lose their tints when subjected to a high degree of heat, and improve in brilliancy and lustre. It is said that the Orientals practise this trick extensively, and sell the altered gems for diamonds. We are not aware of the refractive index of these fire-tested stones having been measured with the view of ascertaining the degree of change; but it is certain that their lustre is increased in a marked degree. Heat, however, does not affect all colored sapphires. Some of the red are often changed to deeper hues, and others are not affected. Brogniart found that the French sapphires from Expailly were actually rendered more intense in color by the action of fire. After numerous experiments with the faint-colored sapphires from Montana, we also have come to the conclusion that the stones from this locality are not perceptibly affected by long-continued heat.

Sir David Brewster, in conducting his famous experiments in optics, was of the opinion that the white sapphire, on account of its structure and its refractive power, was superior to all other transparent minerals for lenses for the microscope. The diamond, which one would naturally suppose to be the most perfect material for the purpose, on account of its high refractive power and apparent clearness, is really faulty, and comparatively worthless on account of its internal structure. If the white sapphire is of such excellence in this respect, on account of its compactness and refractive power, why will not the white zircon prove far superior as a lens, as it is the most compact, transparent, hard mineral known, and its refractive power is much greater than that of the sapphire? Black sapphires are now and then mentioned by authors, but we are inclined to believe that they are very rare; for Davy declares that he met with but two or three specimens in his travels in India or Ceylon. Blue stones of very deep hue appear sometimes quite black; but when they are placed in a strong light, and viewed in another direction, the blue tinge clearly appears. The violet sapphire of perfect hue is a very rare gem, and may be regarded as an accidental stone, being formed of an admixture of the blue and the red. Davy, in all his extended researches in Ceylon, found but two specimens of violet sapphire; and in our examinations of the rough gems from the mines, we are inclined to think the purple spinel is often supposed to be a purple sapphire. Romè de L’Isle found that this variety of sapphire is oftener ruby-violet than sapphire-violet, or that the red tinge prevailed more distinctly than the blue. The lilac-blue are exceedingly rare, and are eagerly sought for by amateurs.

There are some sapphires which exhibit a double play of colors when viewed by natural and then by artificial light. For instance, they may display a decided blue color by day and an amethystine tint by night. D’Auguy possessed a stone that showed in the daylight a beautiful, clear, and sparkling blue, but by candlelight it changed to a royal purple. The cause of this phenomenon is perhaps due to an excess of latent red in the stone, which, however, is not visible in the daytime; but which is called forth by the difference in the illuminating lights, as is shown in their spectra. The hyacinth sapphire is seldom seen, and when perfect is regarded as among the marvels of the species. Dutens possessed a fine one which had been engraved upon by the Greeks.

The subject of the glyptic art, or engraving upon stones, is very interesting to the student who seeks for evidences and traces of the social life of man in early ages. The engraved cylinders of Babylon and Nineveh, with their cuneiform legends, carry us back to traditions two thousand years before the Christian era; and from the engraved scarabei of Egypt and Etruria we form some ideas of the people whose history has otherwise been lost. We may, perhaps, consider the true era of the glyptic art as dating from the time of the Macedonian princes and the Persian conquests, although it had been practised in a rude way from far earlier times. This art of cutting figures upon bright and richly colored, though minute stones, was quite as much admired among the ancients as the laborious skill, with its powerful blows, which produced the heroic statues out of bronze or marble. And perhaps we may say that these gems, in their estimation, were of greater value, not only on account of their beauty and rarity and their minuteness, but also on account of their hardness, which defied the steel instruments of the ordinary sculptor, and yielded only to the dust and splinters of the hardest minerals, like the sapphire and the diamond. We may also safely affirm that the gem-engravers of the Alexandrian and Augustan ages were, in all that concerns excellence of design and composition, rivals of the most famous workers in marble and bronze. These admirable and wonderful artists contrived to enclose within the narrow limit of a little stone all the complicated details of an event in history, or of a fable in mythology; and to make them stand forth in beautiful relief as a cameo, or to sink them down as an intaglio, with all that truth of design and power of expression which characterize the excellence of the largest works of the most consummate masters.

By means of these engraved gems, miniature but accurate copies of some of the celebrated masterpieces and noblest works of ancient sculptors have been preserved to us, while the originals have been destroyed, and even the record of them lost. An instance may be observed in the engraved gem in the Orleans cabinet, which is the only representation we now have of the famous statue of the Repose of Hercules, by Lysippus. As a learned critic has said, in these gems we have the emanations, ever fresh and unfaded, of the feelings and the taste of those ages when the love of the beautiful was the all-prevailing and almost sole religion, and flourished unfettered by tradition, prejudice, and conventional rules; whilst from the universal demand during those same ages for engraved gems, whether for signets or for personal ornaments, artists of the highest ability did not disdain the narrow field of the precious stone as the arena for the exercise of their power. The unparalleled vigor and perfection of many of these performances are a sufficient proof that they proceeded directly from the master’s hand, and were not mere slavish copies, by a mechanic, after designs created by the genius of another. The lovers of the fine arts may derive much benefit from the study of the antique in this particular branch of workmanship. What is there more pleasant than the contemplation of the work of the artists of antiquity; and to behold, shut up, as it were, within the narrow compass of a small gem, all the majesty of a vast design and a most elaborate performance? During the flourishing periods of the Greeks countless statues were carved by numerous artists; and it has been stated that Lysippus alone executed fifteen hundred, all perfect, and some of them colossal. Throughout Asia Minor, Greece, and Italy every town had its temple, gymnasium, or forum peopled with statues of those among her sons who had in any way distinguished themselves in arms, letters, or public games. These became the spoil of the later Romans, and an incredible number were transported to Rome from time to time. Nero is said to have selected from Delphos alone five hundred bronze statues for transportation to Rome. The Etruscan bronzes were quite as plentiful; and Flaccus is said to have carried away in triumph two thousand statues from the sack of Volsinii.

From these statements in ancient history concerning the number of large works in statuary, we can form some idea of the inexhaustible treasury of portraiture in another and oftentimes less costly material. It is estimated that for a period of three hundred years, the engraved gems were manufactured in countless numbers all over the Roman world. It is a little curious that licentious scenes and figures are never or rarely found on antique gems.