Want of certainty about the name applied to the turquoise in classic times leaves us in doubt as to what mystic virtues were then attributed to it. But in the middle ages, the turquoise, like other gems, was believed to have wonderful properties; indeed, it was credited with more supernatural virtues than most of them. The wearer of it had both his sight strengthened and his spirits cheered; he enjoyed immunity from the consequences of a fall by the gem itself breaking, in order to save his bones; and his turquoise, like himself, turned pale if he became sick. When its possessor died, it entirely lost its colour; but recovered it again on passing into the hands of a new owner. In some mysterious way, when suspended by a string, it correctly struck the hours on the inside of a glass vessel. Other precious stones have lost all the marvellous powers that belonged to them for centuries: the emerald no longer relieves the fatigued eyesight; the diamond cannot now dispel fear; the sapphire, though still cold to the touch, has ceased to be able to extinguish fire. In these perverse days, the hailstorm comes down even upon the wearer of an amethyst, and bright red coral attracts rather than repels robbers. But the turquoise still retains one of its mysterious properties, and flaunts it in the face of modern science. Sometimes slowly, sometimes suddenly, it unaccountably turns pale, becomes spotted, or changes from blue to white; and specimens that behave in this capricious manner are found more commonly than those whose colour is distinctly permanent.
The turquoise is called in chemical language a hydrated phosphate of alumina. This means that it consists mainly of phosphoric acid and alumina, along with nearly twenty per cent. of water. It owes its colour to small quantities of compounds of copper and iron. It occurs blue, green, and bluish green; but the change to a pale, mottled, or white colour, which inferior turquoises undergo, generally takes place soon after they are taken from the mine. These colours are opaque, or only very slightly translucent, and the stone has a somewhat waxy lustre. It is only those of a fast ‘sky-blue’ colour that are prized for jewelry; but at one time, a green turquoise was more highly valued than a blue one. Nowadays, however, people have no patience with either precious stones or precious metals that can be easily mistaken for those of inferior value. Either green felspar, which is of the same hardness, or malachite, which is softer, might be mistaken for green turquoise, and both are more common minerals. But there is hardly any other natural stone of the same, or even inferior, hardness that can be confounded with a blue turquoise. The material of some fossil teeth when coloured with phosphate of iron does, however, resemble it. Still, there need be no confusion, because this substance is softer. It is called odontolite or occidental turquoise; while the real stone is known by jewellers as the oriental turquoise. Odontolite is easily recognised under the microscope by the characteristic markings of dentine. Opaque blue glass can be made to imitate the turquoise; but the former differs in lustre and in the nature of its fracture.
Turquoises are found in Tibet, China, and the neighbourhood of Mount Sinai; but, as has been already stated, the supply for jewellers’ purposes comes almost wholly from the celebrated Persian mines. Very little was known about these till a remarkably interesting and exhaustive Report upon them was recently furnished to the British Foreign Office by Mr A. Hontum Schindler, who was for a short time Director of the mines. They are situated in a range of mountains bounding on the north an open plain in the Bâr-i-Madèn district, thirty-two miles north-west of Nishâpûr, in the province of Khorassan. Botanists tell us that the brightest blue is seen on alpine flowers. If pure mountain air could be supposed to brighten the colour of a gem as well as a flower, there is no want of it where these turquoise veins occur. Their position is between five and six thousand feet above the level of the sea, and a strong north wind blows almost continually over the ridges of the hills, rendering the situation very healthy. Wheat, barley, and mulberry trees grow well on the slopes at the lower of these heights.
Geologically, the mountains are composed of sandstones and nummulitic limestones lying on clay-slates and inclosing immense beds of gypsum and rock-salt. But these stratified rocks are broken through and metamorphosed by rocks of igneous origin, such as greenstones and porphyries. The turquoise-bearing veins occur in the metamorphic strata, and the mines proper consist of shafts and galleries in the solid rock. There are also ‘diggings’ in the detritus of disintegrated rock washed down towards the plain, and it is here that some of the best turquoises are found. A number of the mines are ancient and very extensive; and although most of them are now more or less in a state of neglect, Mr Schindler states that the presence of many old shafts—now filled up—for light and ventilation proves that they have at one time been skilfully worked, and were probably then under government control. But they appear to have been, for nearly two centuries, farmed by the villagers, who only think of a quick return for their money, and therefore cut away the rock wherever they see turquoises, without leaving proper supports to prevent the falling in of the mine. Several labourers have at different times been buried in the galleries through the rubbish being badly propped up. The perpendicular depth of one mine is one hundred and sixty feet, and others are nearly as deep. The miners work with picks and crowbars in much the same way as that in which vein-mining is carried on elsewhere; and it is a curious illustration of how slowly long-established processes are altered in the East, that gunpowder should have been used in these mines only within the last thirty years. But it is not strange, as can be seen by some examples of rock-blasting at home, to learn that the results obtained by gunpowder are, in one view, less satisfactory than those got by the pick. The powder does more work, but it is also more destructive, as it breaks the turquoises into small pieces.
Here we may say a few words about how it fares with the people who are occupied with the mining, cutting, and selling of the turquoises. About two hundred men work in the mines or at the diggings, and some thirty more—elders of the village—buy the turquoises and sell them to merchants and jewellers. A certain additional number of hands cut and polish the stones; but this work is done elsewhere, as well as in the district where they are found. The population of the villages in the neighbourhood of the mines is about twelve hundred, and the inhabitants, as in most mining districts, are improvident. Nearly all the men, and not a few of the women, are inveterate opium-smokers. Agriculture is neglected. Turquoise-dealing and its gains make the people careless of anything else. As a rule, the money is quickly spent; and men who easily earn a sum fully equal to fifty pounds sterling per annum, have often nothing to eat.
At the mines, the turquoises are roughly divided into three classes, of first, second, and third qualities. All the stones of good and fast colour and favourable shape belong to the first class. But how curiously these vary in value will be best understood by quoting Mr Schindler’s own words: ‘It is impossible to fix any price, or classify them according to different qualities. I have not yet seen two stones alike. A stone two-thirds of an inch in length, two-fifths of an inch in width, and about half an inch in thickness, cut peikâni (conical) shape, was valued at Meshed at three hundred pounds; another, of about the same size, shape, and cut, was valued at only eighty pounds. Turquoises of the size of a pea are sometimes sold for eight pounds. The colour most prized is the deep blue of the sky. A small speck of a lighter colour, which only connoisseurs can distinguish, or an almost unappreciable tinge of green, decreases the value considerably. Then there is that undefinable property of a good turquoise, the zât, something like the “water” of a diamond or the lustre of a pearl; a fine coloured turquoise without the zât is not worth much.’ He subsequently adds: ‘The above-mentioned three hundred pounds Meshed turquoise was bought from the finder by one of the Rish-i-Safîds (elders of the village) for three pounds; the latter sold it still uncut at Meshed for thirty-eight pounds. As soon as it was cut, its true value became apparent, and it was sent to Paris, where it was valued at six hundred pounds. The second purchaser, however, received only three hundred and forty pounds for it; the difference was gained by the agents.’ Among the fine turquoises in the possession of the Shah, there is one valued at two thousand pounds.
The best stones of the second class are worth about ninety pounds per pound; whilst the most inferior will scarcely bring a twentieth part of this price. The latter are chiefly used in Persia for the decoration of swords, horse-trappings, pipe-heads, and the common kinds of jewelry. Small cut turquoises of a slightly better quality than these sell at the rate of from two to three shillings per thousand. In the third class are included stones unsaleable in Persia, as well as large flat stones, some of which are esteemed for amulets, brooches, buckles, and the like. The prices given there will be more than doubled when the turquoises are sold in Europe.
The turquoise being an opaque stone, it would be useless to cut facets upon it, as these would not reflect light in the same way as when fashioned upon a transparent gem like a diamond or a sapphire. There are three ways of cutting the turquoise, all much in the same style—the flat or slightly convex form, the truncated cone, and the tallow drop or en cabochon. The higher the conical and convex surfaces in the two latter, the more the turquoises are prized. None but a fine deep-coloured stone can be advantageously cut into a conical shape, since one of pale colour would appear almost white at the apex. Turquoises are cut by the hand on wheels made of a composition of emery and gum. They are afterwards polished by being rubbed on a fine-grained sandstone, and then on a piece of soft leather with turquoise dust.
Of the few mines which yield good turquoises, one or two are dangerous, on account of the loose rubbish they contain. The one from which the best of all are obtained yields very few. Some mines contain stones which look well at first, but soon change their colour and fade. Mr Schindler gives an instance of a recently found turquoise, as large as a walnut and of fine colour, being presented to His Majesty the Shah, which he had for only two days, when it became green and whitish, and therefore of no value. Throughout Europe, there has been a great fall in the price of this gem within the last few years, and it would seem that this is owing to the fact that large quantities of stones which appeared to be of fine quality, but were really of fugitive colour, had been disposed of not long ago at good prices. Up to the time that they were sold, their colour had been preserved by keeping them damp; but when taken out of their moist packing, they slowly became white. It need hardly be said that the colour of most precious stones is very permanent. There is, however, a variety of opal occurring in Mexico which is very beautiful when first found; but after a brief time it entirely loses its bright play of colours. Both the turquoise and the opal are peculiar in containing a considerable amount of water in their composition.
The colour of a fine turquoise has not escaped the notice of enamellers and potters. For centuries, an imitation of its characteristic and lovely blue has been applied among other colours to the exquisitely decorated pottery of Persia. On the most expensive and perhaps also the most beautiful of all porcelain, the Sèvres ware of soft body made in the latter half of last century, the turquoise blue is often a conspicuous colour. Towards the end of the century, when the directors of the far-famed fabrique changed the character of the china to that of a hard paste or body, its decoration with a turquoise colour was no longer possible. But modern English porcelain, like the old Sèvres, is of soft paste; and one of the feats on which our great Staffordshire potters pride themselves is the successful production upon it, in recent years, of a soft and clear turquoise blue.