A Treatise on Diamonds, and Precious Stones/Chapter 2
THESE gems are considered to belong to the same class, having the same chemical characters, specific gravity, and hardness, differing only in color.
The perfect Sapphire first claims our attention. When pure, its color is of a clear and bright Indigo blue, united to a high degree of translucency; but it more generally occurs pale blue or cloudy; and not unfrequently transparent in one part, and spotted and streaked of a dark inky blue in the other.—It is found in the streams and rivers in Ceylon, and various parts of India, but more particularly in the kingdom of Pegu, where it is met with in rounded or crystallized fragments, generally small, seldom exceeding the size of a a common nut, though sometimes much larger.
There are several choice specimens in Europe, and one of the finest is in the possession of P. H. Hope, Esq. which weighs 133 carats, and is without a flaw. In perfection this gem is unrivalled, and although not so large as some, it surpasses all in brilliancy and beauty. It is cut in exact proportion, and is set round with brilliants.
Sapphires of less note are by no means rare, and smaller stones of ten or twenty carats are always in the market. They are generally offered for sale in lots cut and polished, consisting of stones of various sizes and quality, and of the value of from twenty to sixty shillings per carat. 1 possess one of eighteen carats, for which I paid £30. The price of stones of three or four carats, may be said to be capricious, depending on thie brilliancy of the gem, and the peculiar beauty of its color.
A very remarkable variety of this gem is the Asteria[2] or Star-stone. This is a semi-transparent sapphire with a pale cloudy tinge, and exhibiting the appearance of a star with six radii, which sparkles with great brilliancy as its position is varied in the rays of the sun.
This gem, when extremely fine, is rare.—The best specimen known, I had the honor to sell for the private collection of his Majesty Louis XVIII.[3]
THE ORIENTAL RUBY
Is esteemed the most valuable of precious stones, and is supposed to differ from the Sapphire in color alone; the hardness, form of crystallization, and specific gravity, being very nearly the same[4].
The color of this gem, when perfect, is, by transmitted light, a cochineal red, presenting a richness of hue the most exquisite and unrivalled; it is however in general more or less pale, and often mixed. with blue, hence it occurs rose red, peach blossom red, and lilac blue, passing into the Amethyst, which we shall notice hereafter.
The monarchs of Pegu, Siam, and Ava, monopolize rubies uf the greatest beauty, as the sovereigns of India have done with regard to the largest Diamonds. The finest ruby in the world is in the possession of the first of these potentates, its purity has passed into a proverb, and its worth in Pegu, compared with gold, is said to be inestimable,—The Subah of Decan is also in possession of one remarkably fine, which he wears as an armlet.
European princes cannot boast of any of first rate magnitude. Henry VIII. is decorated in most of his portraits with a magnificent collar of rubies; but it no longer exists among the Crown jewels, and it is unknown what has become of it.
A superlatively fine ruby of the most enchanting color and greatest perfection, lately arrived in this country; it was purchased by Mr. Hope, whose well known taste and liberality far surpasses any eulogium. This gem has been recut since it came into that gentleman's collection, and may be justly said to be the finest colored stone in Europe.
Rubies of ten carats are extremely rare and valuable; one of twenty-two grains was sold for £160; and another which I possessed, weighing four carats, sold for £60; it would require to be recut, when it would be reduced to thirteen or fourteen grains.
Rubies in lots, Indian cut, of small sizes and of different qualities, are at all times to be had, and sell at from fifteen to sixty-five shillings per carat; but a perfect stone of a carat or six grains may be deemed rare, and falls little short of the value of the Diamond: nay, in some cases, rubies of two, three, or four carats, if very fine, are much scarcer, and even more valuable than diamonds of equal weight.
I Have frequently been called upon to value stones in the India-house, &c. but I have rarely met with a good ruby above a carat and a half.
From this gem I pass to another of the same family, which if it yields in beauty, is yet more rare.
THE ORIENTAL AMETHYST OR VIOLET SAPPHIRE.
This interesting gem appears to unite the blue of the sapphire with the red of the ruby, so nicely blended as to produce the most perfeet violet color. Language is insufficient to express the beautiful hue and lustre of this gem—indeed the captivating effect and fascinating qualities of these precious stones set description at defiance.
The finest Oriental Amethyst in Europe is also in the valuable collection of Mr. Hope; it is of considerable size, though smaller than his sapphire or ruby: it is finely proportioned, and exceeds an inch in its greatest diameter. It has the peculiar property of transmitting, by day-light, the most beautiful and perfect violet color; but by candle-light a decided blue! This stone was in the possession of a nobleman of great taste and judgment, from whose collection it was, for a valuable consideration, transferred to Mr. Hope.
The Oriental Amethyst is extremely scarce, and I have rarely seen one offered for sale, unless very small and inferior in color.
THE ORIENTAL TOPAZ
Is of a light yellow or straw color, and when pure possesses great beauty. It occurs in the same localities with the preceding, is less common than the Sapphire, but not so rare or valuable as the Ruby or Amethyst. When perfect, and skilfully cut and polished, it is highly splendent, and resembles the yellow diamond, for which it may have been sold.
This gem is also of considerable value: a perfect stone of twelve carats, of the finest quality, was sold for above £120; but I have known much larger sold for less; the price depending entirely on brilliancy and perfection. I possess five or six, not very fine, which 1 purchased at forty shillings per carat; they weigh from about two carats to sixteen grains each.
Sapphires exhibiting two colors are occasionally met with, but they may be deenied rare. The ruby and sapphire frequently present a chatoyant or cloudy appearance, which is termed milky, and is considered an imperfection, except in the Asteria, which owes its principal beauty: to this characters I have seen inferior sapphires so dense as to appear black; and I accidentally met with two or three of a dull green tinge, but very different fromthe color of an emerald, Transparent and opalescent sapphires are not uncommon; they possess a considerable degree of brilliancy, but are not to be compared with the diamond, for which, as the French authors assert, they have been often sold.
In preparing stones of this class for the purposes of jewellery, for instance, the sapphire or ruby, the first object to be considered is the intensity of color, which must alone regulate the proportion of the gem, and the sort of work that must be put upon it; taking it as a general rule that the beauty of all precious stones depends on the skill of the workman, for, as an inferior stone is much improved by the best workmanship, so is a fine and perfect gem deteriorated and rendered of little value, if finished by an inferior lapidary.
If a sapphire, ruby, or amethyst is very highly colored, the gem need not have the thickness or depth that a stone of less color would require; the four-sided facets, (steps[5]), may also be made much larger, which will greatly add to its splendor. The table should be large, and must be regulated by the judg~ ment of the workman, as well as the bizel, and which, however low, ought to have double work upon it. If the color is light, the stone will require greater thickness and more work, that is, the facets must be smaller, and separated by ribs at equal distances: the bizel must in this case be higher and full of work, and the table consequently less; aspheroidal form may also be given to the stone. Small facets (technically a deal of work) greatly assist the color, as each facet refracts a portion of the transmitted light to the table, which gives it additional intensity.
The topaz and white sapphire should have considerable thickness, and although they are sometimes cut in brilliant, yet I prefer the steps; as in the latter form, they refract more light, (have more play), and appear with greater lustre.
SECT. II.
Chrysoberyl or Oriental Chrysolite[6] , and Cymophane
The chrysoberyl, though differing in some characters from the sapphire, yet closely approximates to it in hardness and specific gravity. When pure, it is of a gold yellow color inter-mixed with green, exhibiting a peculiar richness of tint, and in lustre yields only to the brilliant.
It occurs in Brazil, in the alluvial soil, associating with diamonds, usually in grains or rounded pieces, and sometimes in crystals: a stone of twenty carats is rarely met with. In that country it is esteemed the most valuable of all colored stones; and although but recently introduced into Europe, it is rapidly rising in public estimation.
The high lustreand exquisite polish which it is capable of receiving, enables it to sustain a competition with the yellow diamond; and so great is its brilliancy by candle-light, that while the transcendant splendor of the diamond destroys the effect of other stones, this is able to support its presence with unimpaired beauty.
This gem is very difficult to be cut, and few lapidaries are capable of doing justice to it. The Chrysolite is the only colored stone that shows to the greatest advantage when formed into brilliant; but thin stones must be cut in steps.
CYMOPHANE, or OPALESCENT CHRYSOBERYL
SECT. III.
On the Ruby—Spinelle and Balais.
The Spinelle, when perfect, is a gem of great value and scarcity; its color is a fine, full carmine or rose red, which varies in intensity; in hardness and specific gravity it is inferior to the oriental ruby, and it differs also in some other characters, which will be described in the Appendix.
It is found in Ceylon and Pegu, of an octahedral form. Small crystals, from one to two grains, are very common, but stones of three carats and upwards are rare, and may be considered nearly of equal value with the oriental ruby.
BALAIS RUBY.
This is a pale variety of the spinelle; it varies in color from light red to yellowish red. It probably derives its name from some supposed locality, or from some peculiar earth, in which it may have occurred.
The Balais possesses considerable beauty, and though not so rare as the spinelle, it is by no means common. It is much admired for its agreeable tinge of color, and, when pure and perfect, sells for a high price, but considerably less than the other distinguished stones of this class.
SECT. IV.
On the Emerald and Aquamarine.
In public estimation, the Emerald ranks next to the Ruby. It is distinguished from all other gems by its color, which is a pure unmixed green, which varies in intensity from the palest possible tinge, to a full and pure body of color, than which nothing can be more beautiful. After beholding the dazzling splendor of the preceding gems, exquisite as they are in beauty and brilliancy, with what quiet pleasure does the sight turn to, and dwell upon the refreshing green of the emerald, calling up in the mind the full verdure of spring, with all the delightful associations connected with the youth of the year, the spring of life!
It appears from Pliny, that the true emerald was certainly known to the ancients, although many other stones, having a green color, were popularly confounded with that gem.
For the last two centuries and more, the only country known to yield Emeralds is Peru, where they occur in Santa Fé,and in the Valley of Tunca. Several large stones have appeared in Europe: about two years ago I cut one, exceeding two ounces in weight, for the Emperor of Morocco, but it was full of imperfections. The largest specimen known is an hexagonal crystal, nearly six inches long, and above two in diameter.
This gem, however small, is so rarely seen perfect, that "an Emerald without a flaw" has passed into a proverb. A fine stone of four carats may be valued at £40 or £50, or even more if very pure. Inferior stones of one or two carats, are sold at from forty to seventy shillings per carat; and if smaller and defective, at ten or fifteen shillings per carat.
The emerald is so highly esteemed in Europe, that it merits the best workmanship. It ought to be cut in planes or steps, larger or smaller, according to the intensity of its color, with a low bizel, and large table, and set on black. With this work it appears to the greatest advantage, especially if also surrounded by brilliants, the lustre of which contrasts agreeably with the softened hue of the gem.
Fine emeralds are rare, and in such demand, that a particular suit has been known to have passed into the possession of a series of purchasers, and to have made the tour of Europe in the course of half a century.
THE AQUAMARINE
Is, as its name implies, a stone of a sea green color, of different shades; sometimes it is greenish yellow, bluish green, and greenish blue. In hardnes it is inferior to the blue topaz, which some varieties resemble, but they may be distinguished by not possessing electricity. The finest stones are from Ceylon and Brazil.
This substance was formerly, and indeed only a few years ago, of considerable value, but it has been found in such abundance in Brazil, Siberia, and latterly in India, from whence vast quantities have been imported, as scarcely to allow it to retain its former rank.
Those only which are of a good color and sufficient depth are manufactured; they have a pretty, lively effect, if in good proportion and well polished. Large stones from one to three or four ounces, are not uncommon, but from their bulk are only in request as specimens for the cabinet[7]; smaller stones, suitable for necklaces, may be bought at low prices, within the reach of every description of purchasers: ring stones may be had at a few shillings each, and larger for brooches or seals from £1 to £5, and often lower. They appear to the greatest advantage when proportioned with a high bizel, table not large, and full of work,
Aquamarines of inferior quality are generally offered for sale in lots, at lower prices than they would have cost in cutting a few years ago. SECT. V.
Yellow, Red, Blue, and White Topaz[8].
In speaking of the Topaz, a gem of a beautiful yellow color is always understood; it is wine yellow of different degrees of intensity; and the fuller and deeper the tinge, the more the stone is esteemed. In hardness it yields to the spinelle.
There are few gems more universal favorites than the yellow Topaz when perfect: the rich warm tone of its color, the vivacity of its lustre, (which it retains even by the side of the diamond), and its large size compared with many others, are characters which deservedly entitle it to distinction; it bears accordingly a high price when of good quality.
It is chiefly employed for necklaces, ear-drops, bracelets, &c. in suit. No little skill and taste are required in cutting and duly proportioning this gem; the table should be perfectJy symmetrical, and not too large, the bizel of sufficient depth, and the collet-side should be formed in delicate steps[9]. It works easily on the mill, and the lapidaries are in general tolerably well acquainted with it; yet it is uncommon to meet with one well cut.
The yellow topaz varies in price according to its beauty and perfection. A superlatively fine stone, perfect in color and workmanship, sufficiently large for an armlet, or any other ornament, and weighing nearly eighty carats was sold for £100.
Topazes have become more common since our intercourse with Brazil, consequently they are less in demand, and lower in price. A fine stone of sixty carats may be purchased at from £20 to £35; and smaller, calculated for ring stones, at from £2 to £5: but it is not usual to sell them by weight.
THE PINK TOPAZ.
Tue pink topaz is made from the yellow, which, when of intense color, is put into the bowl of a tobacco-pipe or small crucible, covered with ashes or sand: on the application of a low degree of heat, it changes its color from a yellow to a beautiful pink[10]. This is performed with little hazard, and if the color produced happens to be fine, the price is much augmented[11],
THE RED TOPAZ.
This beautiful gem, which yery seldom occurs naturally, is of afine crimson color, tinged with a rich brown; it is extremely rare, and generally taken to bea variety of ruby, for which I have seen it offered for sale. Its price, from its scarcity, is quite capricious; it has an exquisite pleasing color, very different from the glare of the artificial pink topaz.
THE BLUE TOPAZ
Is also a beautiful gem, of a fine celestial blue color. It has occurred of considerable magnitude; the finest specimen known I brought in the rough from Brazil; when cut and polished, it weighed above an ounce and a quarter. Smaller specimens are not uncommon, and, when light colored, are often taken for aquamarines, from which they may always be distinguished by their greater weight and hardness, &c.[12]
THE WHITE TOPAZ
Is familiarly called Minas Nova. It is a beautiful pellucid gem, and is used for bracelets, necklaces, &c. It possesses greater brilliancy than crystal, and from its hardness has been used to cover paste, &c.; and to form doublets.
SECT. VI.
Of the Garnet.
The color of the garnet varies from dark to light red or brown; the Syrian is considered the finest, and supposed to be the stone the ancients called the Carbuncle. It is always known by its peculiar color, and better by its great specific gravity. The finest varieties come from India, and some good specimens have been received from Greenland. When large, and free from flaws, they are worth from £2 to £5 or £6, and even more: but stones of this value are of rare occurrence, and always in demand.
Five garnets are never out of fashion, as they can always be worn in mourning. A century ago, a suit of them was considered a magnificent ornament for ladies of distinction. They are much worn in beads, both cut and plain.
Although in hardness the garnet is inferior to many of the gems before mentioned, still it receives a fine polish. On account of the intensity of its color, the table is made very large, and the facets are placed only on the bizel: the under side is frequently hollowed. Thus managed and set on shining foil, whether white or red, the garnet has deceived the purchaser, and has been sold for a better stone. Small garnets are often cut in rose.
SECT. VII.
Amethyst, Yellow Crystal, Rock Crystal, and Cat's Eye,
Sard & Onyx, Opal, and Chrysoprase.
These substances belong to the same class, and differ chiefly in color and translucency. The color of the Amethyst, when perfect, resembles that of the violet or purple grape; but it not unfrequently happens, that the tinge is confined to one part of the stone only, while the other is left almost colorless. When it possesses a richness, clearness, and uniformity of hue, it is considered a gem of exquisite beauty; and as it occurs of considerable size, it is suited to all ornamental purposes.
In specific gravity and hardness, it bears no comparison with the oriental amethyst; it is also inferior in beauty and lustre; though I have often seen the common amethyst offered for sale as Oriental.
Brazil, Siberia, and Ceylon, produce very fine amethysts: they are found in rolled pieces in the alluvial soil, and finely crystallized in fissures of the rock, From the first of these localities, they have lately been imported in such quantities, as considerably to diminish their value: but, as they are the only colored stones, except garnets, that are worn with mourning, they still retain, when perfect, a distinguished rank among the precious gems.
The present price of inferior light colored stones, in the rough state, is about twenty shillings per pound, whilst those of good quality sell at ten or twelve shillings per ounce. Amethysts calculated for brooches or seals, may be purchased at from fifteen shillings to two or three guineas each, for which, ten years ago, treble that sum would have been given.
The amethyst shews to the greatest advantage when cutin steps, with double work upon the bizel; and the table and facets proportioned according to the intensity of the color. A perfect stone, when turned out of hand by a good workman, is a beautiful gem; it contrasts well with fine gold setting, and when surrounded with brilliants has a rich and splendid effect, but alone it loses much of its beauty by candle-light,
YELLOW CRYSTAL—CAIRNGORHM
Is of a beautiful yellow color, and of different shades, from deep to light yellow; also smoky and brown. It is used in various ornaments, as necklaces, &c. but more generally in seals and brooches. Stones sufficiently large for this purpose, may be purchased at from five to ten or fifteen shillings each, and inferior for considerably less.
This substance has also been lately imported in large quantities from Brazil, which has so overstocked the market, that it is now selling at from fifteen shillings to two guineas per pound; whereas a few years ago it sold for three guineas per ounce: it is a beautiful stone, and will most likely become more valuable.—It is often set on foil, and sold for topaz, which it much resembles, but is less brilliant.
ROCK CRYSTAL
Is a transparent substance proverbially clear. It occurs massive and crystallized, filling veins and crevices of rocks; also in rolled pieces in the alluvium, and may be said to be generally distributed in all parts of the world. Small pebbles of crystal are often collected in the vicinity of London, as Bagshot, &c.. which, on account of their cutting glass, and shining when polished, are called diamonds.—We have also Irish and Cornish diamonds belonging to the same class.
Crystal receives a good polish, and is worked into an immense variety of forms; it is much used in jewellery, and commonly set on foil. Larger pieces are cut for the glasses of spectacles, hence called Pebble Spectacles. It is a substance in very general demand, and sells at from two shillings to ten shillings per pound.
THE CAT'S EYE
Is considered to be a variety of crystal, enveloping amianthus.
It is a common substance in Ceylon, from whence great quantities are annually received. It presents a peculiar luminous appearance when held in a strong light, resembling the eye of the animal from which it is named. Its color is generally light grey, yellowish, or reddish brown: a variety, of rare occurrence, is dark green, which exhibits more strongly and in greater perfection the same characters, and is much more valuable and highly prized.
Fine specimens of this stone are held in high veneration by the Cinglese. They are generally used for ring stones, and cut hemispherically,
SARD OR SARDOINE AND ONYX
Are terms not very distinctly understood; they are frequently confounded by writers on mineralogy, and still more so by lapidaries.
The sard or sardoine[13] is considered to be a beautiful variety of chalcedony, and,when perfect, of one uniform tone of color, which is yellowish brown, or reddish brown, of lighter or darker tints, sometimes approaching black; it is more or less translucent when held between the eye and a strong light. When it exhibits angular lines of lighter colors, it is called Oriental Agate. It is generally found in the alluvial soil, and has often been met with in searching for gold and diamonds. It also oceurs stalactitic and forming geodes.
The ancients selected this substance, and the following variety, to engrave upon, no doubt from its possessing two peculiar and necessary qualities, namely hardness and tenacity, by which it is capable of receiving the finest touch or stroke of the tool without chipping, and shewing the art of the engraver to the highest perfection.
Any stone exhibiting layers of two or more colors, strongly contrasted, is called Onyx[14]: as banded jasper, chalcedony, &c. but more particularly the latter, when it is marked with white, and stratified with opaque and translucent lines. But the oriental onyx is considered a substance consisting of two or more layers or bands of distinct and different colors. A sard or sardoine, having a layer of white upon it, would be called an Onyx; and according to the number of layers, it would be distinguished as an onyx with three or more bands: some of the antique engravings are upon onyxes of four bands.
THE PRECIOUS OPAL.
The color of the opal is white or pearl grey, and when held between the eye and the light is pale red, or wine yellow, with a milky translucency. By reflected light it exhibits, as its position is varied, elegant, and most beautiful iridescent colors, particularly emerald green, golden yellow, flame and fire red, violet purple, and celestial blue, so beautifully blended, and so fascinating, as to captivate the admirer. When the color is arranged in small spangles, it takes the name of the Harlequin Opal.—Sometimes it exhibits only one of the above colors, and of these the most esteemed are the vivid emerald green, and the orange yellow. When the stone possesses the latter of these colors, it is called the Golden Opal.
The precious opal is not quite so hard as rock crystal; it is frequently full of flaws, which greatly contributes to its beauty, as the vivid iridescent colors which it displays are occasioned by the reflection and refraction of light, which is decomposed at these fissures, It is never cut in facets, but always hemispherical. It is generally small, rarely so large as an almond or hazel nut, though I have seen some specimens the size of a small walnut, for which several hundred pounds were demanded. At present,a pretty opal may be bought at from one to three, or five guineas, sufficiently large for a pin, or ring stone. It requires great care and judgment in the cutting, as it is fragile, and easily spoiled,
The opal in all ages has been highly esteemed; the history of the Roman senator, who preferred death rather than give up his opal ring to the emperor Nero, is familiar to every one. Among the Eastern nations the opal ranks higher than in Europe.
A spurious substance is sometimes sold for black and green opal, and is often set in jewellery; it ocurs of the size of a small almond, but more commonly not larger than a lentil or pea. This precious gem is nothing more than the cartilage of the hinge of a large shell. Glass, and even scoria, having an iridescent appearance, have also often been sold for opal[15].
THE CHRYSOPRASE
Is of a cloudy pale green color, and has an agreeable appearance: it is translucent, and shews to advantage by. candle-light, more particularly if surrounded by small brilliants.
a Chrysophase of fine quality, and sufficiently large for a brooch or a seal, is worth from two to four or five. guineas. It does not admit of being cut with facets, except round the bizel, which should be low, and the under siderounded. Inferior stones are common, and very low priced.
Carnelians are often extremely beautiful, and deservedly much esteemed, as are varieties of fine mocha stones, agates, and jaspers, whose peculiar characters are strikingly attractive. They are, generally speaking, the most common ornaments set in jewellery, but are not ranked in the class of precious stones.
SECT. VIII.
On the Peridot or Chrysolite.
The peridot, or common chrysolite, is of an olive green color, of more or less intensity. It comes from the Levant, and is commonly found imbedded in lava. Although deficient in hardness and brilliancy, it is, on account of its agreeable color, not unfrequently worked up into necklaces and other ornaments: but owing to its being less hard than crystal, or scarcely harder than glass, it is but little in request.
The tools the lapidary commonly uses, are not fit to polish the peridot; it should be transferred to the glass cutter, who will give it the finest lustre it is capable of receiving: or the lapidary should use glass-cutters' tools, and polish with putty.
When cut in steps, and formed in nice proportion, it will appear to the greatest advantage.
SECT IX.
On the Turquois.
The color of the Turquois is beautiful celestial blue, which migrates into pale blue, and is sometimes tinged with green. It is destitute of that lustre which distinguishes most of the precious stones; it is also opaque, and does not admit of a very high polish; there is, therefore, nothing but its very agreeable hue which can recommend it to the notice of the jeweller. The latter character it possesses in no inconsiderable degree, and retains it unimpaired by candle-light. It has always been fashionable; and although great quantities have been imported, so as to render small stones extremely cheap, yet it has continued to be in considerable demand.
The finest variety is called Turquois Vieille Roche, its texture is uniform and compact. This gem is highly valued in Persia and other Mahometan states, and on that account the most beautiful stones are seldom sent to Europe.
It is doubtful whether the substance termed Turquois Nouvelle Roche is a real Turquois: it is generally supposed to be a fossil bone, colored by Phosphate of Iron; it frequently exhibits evident marks of organization[16].
The turquois is much worn in necklaces, and in every part of ornamental jewellery, from the size of a pin's head, to that of an almond: it contrasts beautifully with brilliants, or pearls set in fine gold, and appears to most advantage when cut spheroidal.
The imitations of this gem are feebly translucent, and lose their beautiful tone of color by candle-light. They are also much inferior in hardness, and have a greater specific gravity.
SECT. X.
Zircon—Hyacinth and Jargoon.
The Hyacinth is of an orange red color, and, when free from defects, is a beautiful and brilliant stone. Small specimens are common in Ceylon, where they are cut and polished; they rarely exceed the size of a bean, but they have occurred large enough for brooch stones. As they are generally full of flaws, they are not often employed in jewellery.
THE JARGOON.
Though differing in color, is of the same class with the preceding. It is a transparent stone, greatly resembling colored crystal, but when polished, it has considerably more lustre. A century ago this gem was considered to be a variety of diamond; it was usually set in rings, buckles, and around stones of little value: at present it is seldom used in jewellery, and therefore bears but a very low price.
TOURMALINE.
Tuts stone is remarkable for its electrical properties. It generally occurs in black and opaque crystals; but the precious varieties are translucent, and of a green, blue, or pink color; they are used for ring-stones, brooches, or seals. By heat or friction it becomes elec tric, and may be distinguished by this property, which it retains many hours.
MOON-STONE.
Is a beautiful translucent substance, of a bluish white color, When cut spheroidal, it reflects a strong light, which appears on the surface of the stone, agreeably contrasting with the pale celestial hue of the gem. It is used chiefly for ring-stones and ear-drops. Fine specimens were formerly sold at high prices; but the recent importations from Ceylon have considerably reduced their value.
SUN-STONE
Is a rich variety of aventurine, which reflects a bright flame-like color, when held in a strong light. It is a silicious substance, and owes its peculiar beauty to the arrangement of its particles, or the dispersion of minute specks of mica in ferruginous quartz. It is rare, and much valued by connoisseurs.
SECT. XI.
On cutting and polishing precious Stones.
The cutting and polishing of precious stones forms the business of the lapidary, an art materially differing from that of the diamond cutter.
The lapidary's apparatus[17] consists of a bench and several mills, adapted to the various operations he has to perform. They receive their motion from a wheel, which is turned with the left hand, by means of a crank. The mill used for cutting or rubbing down the stones, is a horizontal plate of soft lead[18]; its surface is supplied with wet emery powder, which becomes indented in it by the pressure of the stone.
When a stone is to be polished, the lead mill is removed and replaced by one of pewter,which is first prepared by what is termed hacking. This operation is performed by holding the edge of a knife perpendicularly upon it, and turning the mill in contrary directions, until a rough surface is produced. Rotten-stone is then applied to it, with a little water, and the stone is held on the mill until it has received the polish required.
Soft stones, as Opals, Peridots, &c. are polished on mills covered with cloth, and oxide of tin is used with a little water, instead of rotten-stone.
Gems that require nicety in cutting, whether in steps or brilliant, should be given to an experienced workman. The operation is commenced by holding the stone between the fingers until it is rubbed down into the shape required, first forming the table, next the bizel and girdle, and lastly the collet-side, This done, the stone is cemented to a round stick, four or five inches in length. The ribs and facets are formed by holding the stick in an inclined position on the mill, and supporting the other end in a notch on the gin-peg: this instrument is an upright peg, fixed in the bench by the side of the mill, containing holes or notches, one above another, to receive the end of the stick: thus the angle the facet makes with the girdle is greater or less, as the stick is inserted in a higher or lower notch. The peg not only tends to keep the hand steady, but is the cause of the facets being cut true, and always forming the same angle. In step cutting, it is particularly useful; otherwise it would be difficult to place the rows of steps parallel to each other.
To assist the lapidary, quadrants, angles, &e. have been formed with mathematical exactness, in which the stone is placed to be cut and polished; but our workmen have rejected their use, considering them only fit for novices, and depend wholly on tact and a well-practised eye.
The slitting of precious stones, which is a very important branch of the lapidary's business, is performed by a horizontal mill of thin iron, properly hammered, on the edge of which diamond powder is placed, and pressed into it so as to form teeth. Some nicety is required in corning the mill. The best method is to put half a grain of diamond powder in a watch glass, with a few drops of oil, and, with the point of a pen, to place a minute quantity ona small circular instrument, called a Gigger, which is then held against the edge of the mill, while itis gently turned round. By this means the diamond powder is equally distributed. Practical lapidaries usually put a small quantity of powder on a block of steel or a smooth stone, with a drop of oil, and rub it with a muller to separate the particles; they then apply it to the mill with the finger, and set it in the edge by holding a piece of glass against it, at the same time turning the mill round gently.
Oil must be copiously supplied during the operation of slitting; and if the mill be properly corned, it may be worked a whole day without requiring any additional diamond powder. Lapidaries use Oil of Brick, on account of its great fluidity; but as its smell is extremely disagreeable, warm olive oil may be substituted.
THE END.
- ↑ The stones of this class, being superior to all others in hardness and brilliancy, were formerly exclusively called precious. They are all varieties of sapphire—the ruby is sometimes called the Red Sapphire; the oriental topaz, the Yellow Sapphire, &c.
- ↑ The Asteria is produced by cutting the stone across, (en cabochon), and if the primitive crystal (the rhomboid) should be in the centre, the rays of light entering the stone will be refracted and diverge from the angle of the nucleus in the form of a star with six rays.
- ↑ This Asteria is represented in the plate of colored stones: it is considered of unrivalled beauty.
- ↑ The Asteria is also produced in the ruby, by the same cause as in the sapphire. It is very small and of rare occurrence.
- ↑ Colored stones should be cut in steps, see frontispiece, to a point or ridge on the collet-side; and if very thin, the bizel and collet-side should have a spheroidal outline.
- ↑ The common Chrysolite is a different substance, very inferior in hardness.
- ↑ His Excellency Lord Strangford, on his return from Brazil, presented his Majesty with one of the finest hitherto seen.
- ↑ All the varieties have the same hardness and specific gravity.
- ↑ See plate of colored stones.
- ↑ It possesses this property of changing color by heat in common with the blue and yellow varieties of fluor; it also contains fluoric acid; which may be the cause of the change of color produced by heat.
- ↑ Many impositions are practised in forming pink topazes. See appendix.
- ↑ This stone, and the yellow topaz before mentioned, now adorn the magnificent collection of Mr. Hope.
- ↑ The Sard or Sardoine owes its derivation to Sardis, a city of Minor Asia, where a peculiarly fine variety of chalcedony and agate is occasionally found.
- ↑ This stone derives its name from the resemblance which some varieties bear to the marks on the finger nail, and has been extended to all stones haying a banded appearance.
- ↑ See Appendix.
- ↑ This supposition is strengthened by its chemical characters, the Nouvelle Roche always effervescing in acid, which has no effect on the turquois.
- ↑ Portable lapidary's machines are so contrived, that they may be set on a parlour table
- ↑ The oriental stones and chrysoberyl require to be cut on a brass mill, with diamond powder and oil instead of emery and water. They should also be polished on a copper mill with rotten-stone.