Popular Technology Volume II Part 17

8. Gold obtained in any of these methods is always more or less alloyed with some other metal, especially with silver or copper; but a separation is produced, so far as it is required for the purposes of commerce, by two processes, one of which is called _cupellation_, and the other _parting_. The former of these operations consists in melting the gold with a quant.i.ty of lead, which readily oxydizes and vitrifies, and which causes the same changes to take place in the metal to be detached from the ma.s.s of gold. The operation is called cupellation, because it is usually performed on a _cupel_, a vessel formed of bone-ashes, or sometimes of wood-ashes.

9. Cupellation is effectual in removing copper, but not so with regard to silver; the latter is separated by means of a process called _parting_. The metal is rolled out into thin sheets or strips, and cut into small pieces. These are put into diluted nitric acid, which, by the aid of a moderate heat, dissolves the silver, leaving the gold in a porous state.

10. Another process, called _cementation_, is also sometimes used. It is performed by beating the alloyed metal into thin plates, and arranging them in alternate layers with a cement containing nitrate of potash, and sulphate of iron. The whole is then exposed to heat, until a great part of the baser metals has been removed by the action of the nitric acid liberated by the nitre. Cementation is often employed by goldsmiths, to refine the surface of articles in which the gold has been combined, in too small a proportion, with metals of less value.

11. The average amount of gold annually obtained in every part of the globe cannot fall far short of twenty-millions of dollars in value, of which South America supplies about one half, and Europe, about one twenty-fifth part. The amount yielded by the Southern states of our Union, cannot be accurately ascertained, but the whole sum coined at the United States' Mint in 1834, from gold obtained in this quarter, amounted to $898,000, and since 1824 to that time, to $3,679,000. In 1824, the sum was but $5000. Our Southern mines will probably continue to increase in productiveness.

THE GOLD-BEATER.

1. Gold, not being subject to intrinsic change by atmospheric action, or by that of common chemical agents, is extensively used in gilding various substances, either with the view of preserving them from decay, or for the purpose of embellishment. To prepare the gold for application in this manner is the business of the gold-beater.

2. The metal is first melted with some borax in a crucible, and formed into an _ingot_ by pouring it into an iron mould. The ma.s.s is next hammered a little on an anvil, to increase the cohesion of its parts, and afterwards repeatedly pa.s.sed between steel rollers, until it has become a riband as thin as paper.

3. Two ounces and a half of this riband are cut into 150 pieces of equal dimensions. These are hammered a little to make them smooth, and then interlaid with pieces of fine vellum four inches square. The whole, with twenty other pieces of vellum on each side, is inclosed in two cases of parchment. The packet is then beaten on a marble anvil with a hammer weighing sixteen pounds, until the gold has been spread to near the size of the vellum leaves, it, in the mean time, being often turned over.

4. The gold leaves are next divided into four equal squares, with a steel knife on a leather cus.h.i.+on; and the 600 leaves thus produced, are interlaid with a kind of leather or parchment made of the intestines of the ox, and beaten with a hammer weighing twelve pounds, until the leaves have been extended as before. They are again quartered and interlaid, and beaten with a hammer weighing six or eight pounds.

5. The gold having now been sufficiently extended, the packets are taken apart, and the leaves cut to a proper and uniform size, by means of a cane frame on a leather cus.h.i.+on. The leaves, as fast as they are trimmed, are placed in a book, the paper of which has been covered with red bole, to prevent the gold from sticking. Of the two ounces and a half of gold thus treated, only about one ounce remains in perfect leaves, which, altogether, amount to 2000 three inches and three-eighths square. The books contain twenty-five leaves, so that one ounce of gold makes eighty books.

6. Gold extended into leaves, is alloyed, in a greater or less degree, with silver or copper, or both, because, in a pure state, it would be too ductile. The newest skins will work the purest gold, and make the thinnest leaf, because they are the smoothest. The alloy varies from three to twenty-four grains to the ounce, but in general it is six, or one part of alloy to eighty of gold.

7. A kind of leaf called _party gold_, is formed by the union of a thin leaf of gold and a thicker one of silver. The two are laid together, and afterwards heated and pressed, until they have cohered.

They are then beaten and otherwise treated, as in the process just described. Silver, and likewise copper, are also beaten into leaves, although they will by no means bear so great a reduction as gold.

Considerable quant.i.ties of copper leaf are brought from Holland, which in commerce is known by the denomination of "Dutch leaf," or "Dutch gold."

8. The ancient Romans were not ignorant of the process of gold-beating, although they did not carry it so far as we do. Pliny informs us that they sometimes made 750 leaves four fingers square, from an ounce of gold. At Praeneste was a statue of Fortune, gilt with leaves of a certain thickness; hence those beaten to the same degree of thickness were called _Praenestines_. Those of another and less degree of thickness, were called _quaestoriales_, for a similar reason.

9. The Romans began to gild the interior of their houses immediately after the destruction of Carthage. The wainscots of the Capitol were first ornamented in this manner; and afterwards it became fas.h.i.+onable to gild the walls and ceilings of private dwellings, as well as articles of furniture.

10. _Gold wire._--The ductility of gold is more conspicuous in wire than in leaves. The wire thus denominated, is in reality silver wire covered with gold. It is formed by covering a silver rod with thick leaves of gold, and then drawing it successively through conical holes of different sizes, made in plates of steel. The wire may be reduced, in this manner, to a degree of extreme fineness, the gold being drawn out with the silver, and const.i.tuting for it a perfect coating.

11. Wire thus formed is often used in the manufacture of _gold thread_. Before it is applied in this way, it is flattened between rollers of polished steel, and then wound on yellow silk by machinery.

The coating of gold on the silver wire employed in this way, does not exceed the millionth part of an inch in thickness.

THE JEWELLER.

1. The jeweller makes rings, lockets, bracelets, brooches, ear-rings, necklaces, watch-chains, and trinkets of like nature. The materials of the best quality of these ornaments are gold, pearls, and precious stones, although those of an inferior kind are often used.

2. There are several stones to which is applied the epithet _precious_, of which the following are the princ.i.p.al: the diamond, the ruby, the sapphire, the topaz, the chrysolite, the beryl, the emerald, the hyacinth, the amethyst, the garnet, the tourmalin, and the opal.

To these may be added rock crystal, the fine flints of pebbles, the cat's-eye, the oculis mundi or hydrophanes, the chalcedony, the moon-stone, the onyx, the carnelian, the sardonyx, agates, and the Labrador-stone. These stones, together with different kinds of pearl, are also called gems or jewels.

3. The precious stones are valuable, as articles of merchandise, in proportion to their scarcity, weight, transparency, l.u.s.tre, and hardness. In most of these particulars, the diamond is superior to any other; but those of the same size are not always of equal value, for all are not of the same color or brilliancy. The very best are said to be _diamonds of the first water_. The diamond was called adamant by the ancients, although this term was not confined exclusively to this stone.

4. The weight and consequent value of the most precious stones are estimated in _carats_, one of which is equal to four grains troy weight, and the value of each carat is increased in proportion to the size of the stone. In England, the cost of a cut diamond of the first water is thus estimated:

1 carat is = _l._8 2 do. is 2 2 8 = 32 3 do. is 3 3 8 = 72 4 do. is 4 4 8 = 128

By the foregoing examples, it will be seen that the weight is multiplied by itself, and the product by the price per carat, which may be some other sum, according to the general characteristics of the stone.

5. This rule, however, is not extended to diamonds of more than 20 carats in weight; nor is this or any other rule of estimate strictly adhered to in every case; nevertheless, it probably comes pretty near to general usage. In the same country, a perfect ruby of 3-1/2 carats is worth more than a diamond of equal weight. A ruby weighing one carat may be worth 10 guineas; two carats, 40 guineas; three carats, 150 guineas; six carats 1000 guineas. A ruby of a deep red color, exceeding 20 carats, is called a carbuncle; and of these, 108, weighing from 100 to 200 carats each, are said to have been in the throne of the Great Mogul.

6. Some of the European sovereigns have, in their possession, diamonds of great value, several of which were originally brought to England from India. The _Pitt_ or _Regent diamond_ was purchased in India by Robert Pitt, grandfather of the Right Honorable William Pitt, for 12,500 sterling. It was brought to England in a rough state, and 5000 were there expended in cutting it; but the cuttings themselves were worth 7000 or 8000. It was sold to the Duke of Orleans, for the King of France, at the enormous price of 136,000. Its weight is 136 carats; and, before it was cut, it was as large as a common pullet's egg.

7. A celebrated diamond, in the possession of the emperor of Russia, is denominated the _Effingham_ or _Russian diamond_. It was brought to England by the Earl of Effingham, while governor-general of India, and sold to the Empress Catharine for 90,000. It is inferior in shape to the last mentioned, but superior to it in magnitude, it weighing 198 carats. The Queen of England has a diamond which cost 22,000.

8. The largest diamond hitherto known was found in the island of Borneo, and it is now in the possession of the Rajah of Mattan. Many years ago, the governor of Batavia offered, in exchange for it, $150,000, and two large brigs of war with their equipments and outfit; but the rajah refused to part with the jewel, to which the Malays supposed miraculous power belonged, and which they believed to be connected with the fate of his family. The weight of this diamond is 367 carats.

9. Other jewels, belonging to different sovereigns, as well as to private persons, might be mentioned; but a sufficient number has been noticed to enable the reader to form some idea of the extravagant expenditures often made for articles of imaginary value. We will merely add that the royal family of Portugal is in possession of a stone which was formerly supposed to be a diamond, but which has lately proved to be some kind of crystal of little value. The weight of this stone is 1680 carats; and, until its real character was discovered, it was valued at 224 millions sterling.

10. The value of precious stones was much increased in ancient times, by the absurd notion commonly entertained, that they possessed miraculous powers in preventing or curing diseases, as well as in keeping off witches and evil spirits. These notions still prevail more or less in heathen nations; and many, even in countries called Christian, wear them, or something else, as amulets for the same or similar purposes.

11. _The Gem-sculptor._--Figures and letters are often cut in precious stones by the gem-engraver, or gem-sculptor, whose art, according to the opinion of some writers, originated with the Babylonians; but, according to others, it had its commencement in India or Egypt. In the latter country, it was first employed in the production of hieroglyphical figures on basalt and granite rocks. This art, which is denominated lithoglyptics, or the glyptic art, was held in great estimation by the Greeks in ancient times. It arose to eminence with the other fine arts; and, like them, it had its zenith of perfection, was buried with them in the ruins of the Roman empire, and with them revived towards the end of the fifteenth century.

12. The productions of gem-sculpture are chiefly of two kinds. The first of these are _cameos_, which are little bas-reliefs, or figures raised above the surface. They are commonly made of stones, the strata of which are of different colors, so that the figure is different in color from the ground on which it has been raised. The other productions of this art are denominated _intaglios_. The work of these is the reverse of that first mentioned, since the figure is cut below the surface of the stone, so that they serve as seals to produce impressions in relief upon soft substances.

13. This artist performs his work by means of a lathe, with the aid of diamond dust. The instruments are made of soft iron, and are fixed in leaden chucks, which can be readily fastened to one end of the mandril. The diamond dust is made into thin paste with olive oil, and is applied to the point of the instrument. The small invisible particles insinuate themselves into the iron, where they remain permanently fixed. In producing figures and letters with a tool thus charged with the hardest substance in nature, the precious stone is brought in contact with it while in rapid motion.

14. The engraved gems of antiquity have been greatly esteemed, as works of art, by the curious, and various methods have, therefore, been devised to imitate them. This has been done in gla.s.s in such perfection, both as to form and color, that good judges can scarcely distinguish the imitations from the originals. The impression of the gem is first taken in some kind of fine earth; and, upon the mould thus formed, the proposed material is pressed, while in a plastic state.

15. The precious stones generally have likewise been imitated with great success. The basis of the different compositions is a _paste_ made of the finest flint gla.s.s, the materials of which have been selected and combined with great care. The desired color is produced with metallic oxydes. A great number of complex receipts are in use among manufacturers of these articles.

16. _The Lapidary._--The precious stones and imitations of them in gla.s.s are brought to the desired form by the lapidary. The instrument with which this artist chiefly operates is a wheel which is made to revolve horizontally before him. It is put in motion by means of an endless rope extending from another wheel, which is moved with the left hand of the operator, while, with his right, he holds, in a proper position, the substance to be reduced.

17. The precious stones, being of small size, cannot be held with steadiness on the wheel with the hand, nor with any holding instrument; they are, therefore, first fastened, by means of sealing-wax, to the end of small sticks. By this simple means, and a small upright post, against which the hand or the other end of the stick is rested, the workman can hold a stone in any position he may desire.

18. The lapidary's wheel is made of different kinds of metals. The diamond is cut on a wheel of soft steel, by the aid of its own dust mixed with olive oil. The Oriental ruby, sapphire, and topaz, are cut on a copper wheel in the same manner, and polished with tripoli and water. Stones of a less degree of hardness are cut and polished on a leaden or tin wheel with emery and rotten stone.

19. The ancients were not acquainted with any method of cutting the diamond, although they applied its powder to polis.h.i.+ng, cutting, and engraving other stones. Gems of this kind, either rough, or polished by nature, were set as ornaments, and were valued according to the beauty and perfection of their crystallization and transparency. The value of any precious stone, or jewel, depends much upon the skill of the lapidary.

20. _The Pearl-fisherman._--Pearls are obtained from a testaceous fish of the oyster kind, found in the waters of the East and West Indies, as well as in other seas of different lat.i.tudes. These oysters grow in some parts of the globe, in cl.u.s.ters, on rocks in the depths of the sea. Such places are called _pearl-banks_, of which the most celebrated are near the islands of Ceylon and j.a.pan, and in the Persian Gulf. The finest and most costly pearls are the Oriental.

21. Pearls are considered by some to be morbid concretions, or calculi, produced by the endeavor of the animal to fill up the holes which may have been made from without by small worms. Others suppose them to be mere concretions of the animal juice about some extraneous matter which may have been intruded by some means into the sh.e.l.l.

22. To collect the sh.e.l.ls containing these singular productions, is the business of _divers_, who have been brought up to this dangerous occupation. They must generally descend from eight to twelve fathoms, and must remain beneath the surface of the water for several minutes, during which time they are exposed to the attacks of the voracious shark. In addition to the danger from this cause, the employment is very destructive of health.

23. In preparing a diver for his descent, a rope is tied round the body, and a stone, weighing twenty or thirty pounds, is fastened to the foot to sink him. His ears and nostrils are filled with cotton, and a sponge dipped in oil is fastened to his arm, to which he may now and then apply his mouth, in order to breathe without inhaling water.

In addition to these equipments, he is furnished with a knife, with which the sh.e.l.ls may be detached from the rocks, and with a net or basket, in which they may be deposited.

24. Thus equipped, he descends to the bottom, and having filled his depository, or having stayed below as long as he may be able, he unlooses the stone, gives the signal to his companions above, who quickly draw him into the boat. At some pearl-fisheries, the diving-bell is employed, which in some degree obviates some of the dangers before stated.

25. The sh.e.l.ls thus obtained are laid by, until the body of the animal has putrified, when they commonly open of themselves. Those which contain any pearls, generally have from eight to twelve. The pearls having been dried, are a.s.sorted according to their various magnitudes; and, to effect this separation, they are pa.s.sed through nine sieves of different degrees of fineness. The largest pearls are about the size of a small walnut; but such are very rare. The smallest are called _seed pearls_.

26. Pearls are of various colors, such as white, yellow, lead-color, blackish, and totally black. The "white water" is preferred in Europe, and the "yellow water," in Arabia and India. In regard to their form, they vary considerably, being round, pear-formed, onion-formed, and irregular. The inner part of the pearl muscle is called _nacre_ or _mother of pearl_, and this is manufactured into beads, snuff-boxes, spoons, and a variety of other articles.

27. Pearls were objects of luxury among the ancients. A pearl valued by Pliny at a certain sum, which, reduced to our currency, amounts to $375,000, was dissolved by Cleopatra, and drunk to the health of Antony, at a banquet. These beautiful productions are not estimated so highly at present. The largest will sometimes command four or five hundred dollars, although very few, which are worth over forty or fifty dollars, are ever brought to this country.