This name (sapphire) is derived probably from the Hebrew, as it is often mentioned in the Bible. It is not certain whether’ the ancients were acquainted with the blue variety only of this gem, and were ignorant of other blue stones, such as lazulite, fluorspar, &c. It was not used by them as a gem, probably on account of the difficulty of working it; but as a medicine, many peculiar virtues were ascribed to it. This species has hitherto been usually divided according to its different colors. The name of ruby has reference to a red color, and was applied by the ancients to the carbuncle.
Sapphire occurs in crystals, in rounded grains, and pebbles. It is generally transparent, but sometimes only translucent, or displays a shine of light of six rays, resembling the form of a star. It possesses double refraction in a slight degree, and a vivid vitreous lustre, which sometimes turns to that of mother of pearl.
Its fracture is from conchoidal to uneven. Its principal colors are blue and red, with their various shadings; sometimes white, gray, yellow, green, brownish-greeu, and black. If the red sapphire (ruby) is exposed to a great heat, it becomes green, but when cold, returns to its original color; the green sapphire undergoes no changes.
The sapphires which sometimes display a peculiar play of light are divided into—
1st. Star sapphire (asteria, opalescent, or chatoyant sapphire). Some translucent sapphires display, if held before the sun, or a burning taper, a white light running in six rays, resembling three white planes, or stripes crossing themselves at one point. This property is thus visible when the sapphire is cut convex (or cabochon), and when the principal axis of the crystal stands perpendicular to the base of the convex cut stone ; these star sapphires are either called ruby-asteria, sapphire-asteria, or topaz-asteria, according to the color they bear.
2d. Girasol sapphire, Oriental girasol, sunstone sapphire, or ruby cat’s-eye, have a yellowish, reddish, or bluish shine, or reflection of light, generally of a lighter color than the stone itself, displayed when moved or turned on the convex surface.
Sapphire is composed of pure alumina; the opaque contains about one per cent, oxide of iron and one per cent, silica; before the blowpipe it is unaltered; fuses with borax and salt of phosphorus, but is not attacked by the strongest mineral acids ; friction excites electricity, and in the polished specimens the electrical attraction continues for a considerable length of time.
The perfect and colorless sapphire has a brilliant lustre, so that the same may be confounded with the diamond; its hardness is inferior to the latter. The specific gravity of the blue sapphire- is 3.979; of the ruby, 3.909; of the green (Oriental emerald), 3-949; of the violet (amethyst), 3.921.
The various names given to sapphire, according to its color, are—
1st. Ruby (Oriental ruby), of a dark crimson red, cochineal or carmine, and rose-red, mostly inclining to violet-blue.
a. Oriental hyacinth, aurora-red.
2d. Oriental amethyst, palish violet-blue; playing sometimes in rose and purple red, like the common amethyst, except in its superior lustre.
3d. White sapphire, limpid and perfectly transparent; vivid lustre, resembling the diamond.
4th. Sapphire, Oriental sapphire, from the darkest to the lightest blue, with different shadings, whence it is denominated by different terms, such as male sapphire, of a perfectly clear Berlin or smalts blue; female sapphire, full blue, with a tinge of white—sometimes sky-blue, with streaks or specks; water sapphire, very pale-blue, and sometimes discolored; cat sapphire, blackish or greenish blue, often not transparent.
5th. Oriental topaz; lightly yellow, lemon, or brownish straw yellow, sometimes playing into green ; it is distinguished from the common or true topaz by color and lustre, but it occurs likewise much larger, and is seldom less free from faults than any other species of sapphire.
6th. Oriental aquamarine; greenish blue, pure and transparent, possessing a higher lustre and greater hardness than the common aquamarine.
8th. Oriental emerald; green, more or less dark, inclining to yellow; it does not equal in color the real emerald, but possesses a higher lustre, and is at the same time very rare.
The sapphire was well known to the ancients. Pliny gave a description of the star’ sapphire, under the nartie of asteria. The sapphire possesses the double refraction in an indifferent degi’ee, and its fracture is unequal and conchoidal. The finest ruby sapphire occurs in the Capelan mountains, near Syrian, a city of Pegu, in the kingdom of w a ; also in the sand of the Expaillio river, in Auvergne.
Blue sapphires are brought from Ceylon. Large masses of blue sapphire, of opaque color, have been found in North Carolina, as well as some isolated crystals in Buncombe County, North Carolina; but there are many more localities in the United States, such as New Jersey, New York, and Connecticut. Sapphires are mostly found in the sands of rivers, or in boulders, with garnets, zircons, kyanite, and in basalt.
It has been observed that the blue sapphires are frequent in Ceylon, but not the rubies, and that in Pegu it is the reverse. The most celebrated mines of sapphire are at Mo-gaot and Kyat-Pyan, five days’ journey from w a . The Boa, or-Emperor of the Birmans, retains all the larger sapphires.
For cutting a sapphire an iron mill is used, and for polishing, a copper mill, or one made of alloy of lead and tin, to which a horizontal motion is given by a very simple machinery ; its surface is charged with diamond powder and oil, or with fine emery and water. A thick peg or gauge of wood, pierced with small holes in all directions, is set upright on the lapidary’s bench, close to the mill.
The stone, being placed on the surface of the mill, and the opposite end of the stick to which it is cemented being inserted in one of the holes of the gauge, the mill is put in motion by turning a winch, and the stone kept steady on it. When the stone has all the facets, the cutting mill is taken out and replaced by one of brass, on which the polishing is performed by means of fine emery and rotten-stone, in the same manner as before.
A good judgment is required in determining the form and proportions best adapted to set off any particular stone to the best advantage. If the color is full and rich, its transparency perfect, and its refractive power considerable, the best form to give it is the brilliant. If, on the contrary, the color is dilute, the most advantageous method of cutting it is, to cut the table side (pavilion) brilliant fashion, and the collet side (culasse) in steps; by this means the table itself will be left dark, while all the light reflected from the steps on the under side of the stone will be thrown up into the facets, by which the table is surrounded.
The French lapidaries cut the most perfect sapphires in a square or octagon form, with a single delicate step between the table and the girdle, and three or four steps between the girdle and the collet. If the sapphires possess a varying chatoyant lustre, or are of a small size, their form is always hemispherical or elliptical, without any flat facets; the flatter the ellipse the more the varying lustre is diffused over the surface of the stone ; whereas with a high ellipse it is condensed on a single spot.
In setting sapphires we always use foil answering to their color. The ruby is set with a reddish gold foil, or a foil of copper or red glass; the blue sapphire with a silver foil, or blue-colored foil, or with feathers of blue ducks, pigeons, or peacocks; and the water sapphire in a black back : but all perfectly pure sapphires are set d jour.
Many sapphires may be deprived of their specks by a careful calcination in a crucible filled with ashes or clay, and they assume then a more agreeable and purer color and greater transparency. Sapphires are very favorite gems, and are extensively used by jewellers for setting in pins, lings, &c. In China, the ladies’-slippers are mounted with rubies.
The blue sapphires have of late been employed as lenses for microscopes with great success. According to Brewster, it is, for its refracting power, second only to the diamond, and superior to all other gems. A new use has lately been made of the sapphire for drawing wires—it being cut in the form of a wedge, through which, by means of a diamond-point, a circular hole is drilled and then fastened on a brass plate; the wire is drawn through the smaller aperture of the sapphire towards the wider, by which process it is reduced to a thinness never otherwise attained.
The price of sapphires is very relative, but their proportional value is next to that of the diamond. The Oriental ruby stands highest in value, and when perfect, and exceeding three carats, is generally as dear as a diamond of equal weight and quality. After the ruby, blue sapphire stands next in value ; and as this is not so rare, and occurs in large specimens, it is not so high in price.
Some put the price of the blue sapphire equal to that of the colored diamonds; others put the price at half that of a brilliant under similar circumstances. Sometimes the value is fixed by multiplying half the price of a sapphire weighing a carat, with the square of its weight. It is therefore very difficult to come at an exact price-current, and the following average prices come nearest to their commercial value: