An oriental Diamond formerly belonging to Nadir Shah, Sultan of Persia, deserves the next place: it is without flaws or faults of any kind, and weighs 193 carats. Its form is that of a flattened ovoid, and it is about the size of a pigeon’s egg.

The next in size is a rough Brasilian Diamond, found in the river Abatio in, possession of the Prince Regent of Portugal weighing near an ounce troy.

The Pitt or Regent Diamond, is said to, have been found in Malacca, It was purchased by Mr. Pitt, an English gentleman, then Governor of Bencoolen in Sumatra, and was sold by him to the Regent Duke of Orleans by whom it was placed among the crown jewels of France, and of which it still forms the great glory. It is cut in the form of a brilliant, and is absolutely faultless. It weighs 136 carats, and its value as estimated by a commission of jewellers in the year 1791, is twelve millions of livres.

Perhaps one of the largest and most beautiful coloured Diamonds is a rich sky-blue brilliant, belonging to the crown jewels of France: it weighs 67 carats, and is estimated at three millions of livres.

In this list I have not enumerated the supposed great Diamond of Portugal, because it is now the general opinion, both of mineralogists and jewellers, that this stone is a white topaz. It was found in Brazil, in the Diamond mines, is as yet in its rough state, and weighs 1680 carats, above eleven ounces.

From the centre to the circumference of the iron plate are lines or shallow grooves formed by rubbing it in that direction with a fine-grained gritstone; these grooves serve to retain the mixture of oil and Diamond powder with which the plate is charged. In order to keep the Diamond perfectly steady while the polishing of each facet is going on, the following contrivance is had recourse to. A copper cup (called a dopp) about three quarters of an inch in depth and in width, and furnished with a stem about four inches long of stout copper wire, is filled with plumbers’ solder, which also projects in a conical form beyond the rim of the cup: in the apex of this cone, the solder being softened by heat, the Diamond is imbedded with one of the facets projecting.

The stem of the cup is now put into very powerful pincers, which screw up with a nut and a wrench or lever, and thus hold it perfectly tight. The handles of the pincers (called tongs) are of wood, are broad and terminated by two feet, about an inch high, so that when laid horizontally they are supported exactly as a pair of candle snuffers is, the studs fixed to the handles of the snuffers representing the legs of the pincers, and the single stud near the point of the snuffers representing the inverted copper cup holding the Diamond, and at the same time having its stem strongly griped by the pincers. In this position the Diamond is placed on the plate, the pincers resting on their legs on the wooden bench or table that supports the plate, and pressing at the same time against an upright iron peg; the broad part of the pincers between the legs and the Diamond, is then loaded with weights, both to steady the machine, and to increase the pressure of the Diamond against the skive.

Matters being thus adjusted, a little oil and Diamond powder is dropped on the plate, it is set in motion at the rate of about 200 revolutions in a minute, and the process of grinding down, and at the same time of polishing is begun. The Diamond is taken up and examined from time to time, and is adjusted so as to give the facet its true form. The heat occasioned by the friction is at all times pretty considerable, and when the pincers are heavily loaclen it occasionally increases to such a degree as to soften the solder and displace the Diamond. This is a serious accident, frequently occasioning a flaw in the Diamond, and always tearing up the surface of the skive so as to damage it very considerably. There is room on the skive for three or four Diamonds at the same time; and to give each its proper share of attention is as much as one person can well manage. The completion of a single facet often occupies some hours.

Diamonds are brilliant cut, rose cut, and table cut. The brilliant is deservedly in the highest estimation, as it is the form which shows to the greatest advantage the peculiar lustre of this gem. The proportions and method of forming the brilliant are described by Jeffries; and with regard to the shape and position of the facets no change has hitherto taken place, although, from the present fashion of preserving as great a spread or surface as possible, the rules for proportioning the dimensions of the brilliant are by no means strictly adhered to.

The brilliant may be considered as formed of two truncated pyramids united together by one common base, the upper pyramid being much more deeply truncated than the lower one. The plane formed by the truncature of the upper pyramid is called the table (a); that formed by the truncature of the lower is called the collet (b); the common base is called the girdle (c); the space between the table and the girdle is the bizel (d) and that between the girdle and the collet is the collet-side (e).

Both the table and the collet are regular octagons; the bizel is formed by eight lozenges and twenty-four triangles; the collet side is occupied by four irregular pentagons alternating with as many irregular lozenges, radiating from the collet as a centre, and usually called the pavilion facets, and bordered by sixteen triangular facets, adjoining the girdle. The brilliant is set with the table side upwards, and the collet side implanted in the cavity made to receive the Diamond.

The regular rose Diamond, is the form given to those stones the spread of which is too great in proportion to their depth to admit of being brilliant cut, without a great loss of substance. It is formed by covering the whole surface of the stone with equilateral triangles, each pair being placed base to base, so as to form a kind of rhomb.

The table Diamond is the least beautiful mode of cutting, and is applied only to those stones or rather fragments, which with a considerable breadth have only a very trifling depth.

Good stones, from one to four or five carats, if skilfully cut either into brilliants or rose Diamonds, lose in the process somewhat less than half their weight; hence the value of a cut stone is twice that of a rough stone of equal weight, independently of the cost of cutting.

The Diamond-cutters of England are confessedly the best in Europe, but their number is unfortunately so small as to, occasion many stones to be sent to Holland ; where, from the greater number and more active competition of the artists, the price of workmanship is considerably lower, but in at least an equal degree inferior to that of London. Brilliant cut Diamonds are so infinitely superior to the others, that of late many rose-cut stones from Holland have been recut into brilliants, notwithstanding the additional expence and the loss of size necessarily attendant on this operation.

Diamonds themselves are always equally in fashion, but the mode of setting them varies according to the caprice of taste or the desire of novelty : hence the jeweller has perpetual opportunities of exercising and displaying the inventive elegance of his taste in the assortment of hues and the arrangement of groups. He will cluster together the smaller stones so as to aggrandize and enhance the effect of the whole; the larger and more perfect ones will generally be set open and displayed to the greatest advantage, while the inferior ones will be assisted by setting them solid on black, or, if need be, with coloured foil.

But whatever be the occasion that calls forth his art, whether the construction of a star, a bandeau, a tiara, a plume, a necklace, or an ear-drop, he will bear in mind that his greatest merit is the concealment of his art: the display of belts and borders of gold can add nothing to the superlative splendour of the Diamond.

Silver fades in the presence of gold, gold itself yields to the more brilliant and costly materials of the jeweller, and of these the most beautiful, the most costly, the very perfection of the gem creation is a colourless brilliant without speck or flaw, large enough to attract notice, yet not so bulky as to be cumbersome in itself, or too disproportionate to the smaller ones with which it is associated.

We have seen a large and costly Brazilian diamond fractured accidentally in two by some such means ; but if we remember right, this was occasioned by a fall, after having been subjected to heat. Many authors have permitted their fancy to rove on some attribute peculiar to the diamond, either real or supposed; thus, we are told, that a diamond is softened and broken if steeped in the blood of a goat; but not, according to others, unless it be fresh and warm, nor even then, fractured without blows; and that it will also break the best hammers and anvils of iron.

Sir Thomas Brown says, that a diamond being steeped in goat’s blood rather receives thereby an increase of hardness; ” for,” he observes ” the best we have are reducible to powder without it; and are so far from breaking hammers, that they submit to pistillation, and resist not an ordinary pestle.”
The truth is, as far as the goat’s blood is concerned it makes no difference either way ; and we know very well that it is a matter of no difficulty to crush the diamond in a steel mortar; from its lamellar texture it is also capable of being split and cleaved, and jewellers are by these means enabled to work it. The test of a diamond, in the Brazils, we believe to be this: when placed on a hard stone, and struck with a hammer, if it either resist the blow, or separate into laminae, it is concluded to be one. The introduction of a steel point will easily separate the laminse of the diamond. Small round diamonds cannot however be split.

From the extreme brilliancy of the diamond, and its purity, it was consecrated to all that was celestial, and accordingly supposed that it would triumph over all means employed to subdue it, the solar ray, excepted. It did triumph indeed over the hot furnaces to which it was exposed in the crucible of the alchymist, but the spell which united it to the sunbeam is now dissolved, and it has yielded to the severity of the ” torture and inquisition” of modern chemistry. Newton, reasoning from its great density and high refractive property, concluded that the diamond was combustible, or, to use his own language, ” an unctuous substance coagulated,” though he was in some measure anticipated by Boetius de Boot, in 1609. The event has amply verified this conjecture, and the Tuscan philosophers and the Honourable Mr. Boyle ascertained the fact.

The first grand experiment to prove the combustibility of the diamond took place in the presence of Cosmo the III. Grand Duke of Tuscany, wherein the diamond being exposed in the focus of the great lens (still in the Grand Duke’s laboratory at Florence), it was entirely volatilized. Guyton de Morveau, and others, consumed the diamond, and it was readily dissipated in the focus of the great mirror of Tchirnhausen, as we believe it subsequently was in that of Parker’s burning lens. In the year 1771, Macquer observed the diamond to inflame. Guyton de Morveau had proved that the diamond was destroyed when projected into red-hot nitre; and it was also burnt by means of melted nitre in a gold tube, by Mr. Tennant.
When fragments of diamond were introduced into the brilliant arch of flame, evolved between points of charcoal in the galvanic batteries of the Royal Institution, consisting of 2,000 double plates, and exposing a surface of 128,000 square inches, they rapidly disappeared, being completely volatilized. The diamond may be easily consumed by being placed in a cavity of charcoal, and urging on it the flame of a spirit lamp, by means of a stream of oxygen.

So far the combustibility of the diamond was completely ascertained, but its nature remained still undetermined. Lavoisier had proved and pointed out that carbonic acid gas was evolved as a product both in the combustion of the diamond and that of charcoal, and thus their identity was inferred. The researches of Clouet, Messrs. Allen and Pepys, and others, have confirmed this conclusion- Sir George Mackenzie converted iron into steel by powdered diamonds. Mr. Children’s immense battery consisted of twenty triads, each six feet long, by two feet eight inches broad, exposing a total surface of thirty-two feet; when iron, with diamond powder interposed, was exposed to its influence, the iron was converted into steel, and the diamond disappeared; and Mr. Smithson Tennant, having placed a diamond in a gold tube, supported in a state of incandescence ; a stream of oxygen, by means of gentle pressure, was made to traverse it, and the result proved that the oxygen was transformed into an equal volume of carbonic acid gas, which was found in an opposite receiver resting over mercury.

Sir Humphry Davy, when at Florence, made some experiments with the Grand Duke’s burning lens, on the combustion of the diamond. He found that when the gem was introduced into a glass globe supplied with oxygen, and kindled by the lens, it continued to burn after it was removed from the focus—the oxygen was supplanted by an equal volume of carbonic acid gas, while there was no deposit of aqueous vapour. On the other hand, when plumbago and charcoal were consumed under similar circumstances, there was a sensible diminution of volume, and also a formation of watery vapour, clearly proving that the latter contained hydrogen.

It was once stated that some approximation had been made to the formation of the diamond in the laboratory of the Royal Institution, with their extensive galvanic battery. By acting on charcoal in vacuo, minute hard crystals were said to be formed round the superior wire. Our informant, however, had but an indistinct idea of the mode adopted, and the general features of the experiments ; and as it has never been announced or described, in all probability there is some mistake in the case. It does not seem to us at all probable that diamonds are likely to be formed by an artificial process, though we know the attempt has been made both by means of the galvanic battery and the compound-gas blowpipe; no fear need, however, be apprehended from any such rivalry, more than from the method of forcing by artificial means the unio margaritifera or meleagrina margaritifera to form pearls at command. These molluscs either would not obey the commission, or they were misshapen, unsightly, and worthless.

Spherules of shells, or some other substance, flattened at the bottom, are forcibly inserted between the animal and the shell, in such a way as the animal may not be able to displace them. These, in a short time, are covered with a layer of pearly matter, which is supposed to be secreted by the mantle. It has been stated in France, that a solution of phosphorus in sulphuret of carbon yields minute diamonds. We have been in the habit of using this compound for many years, and have never discovered any thing of the kind; and the diligent search we have made, since this strange announcement, has been equally unsuccessful—we believe diamonds are not so easily formed. From the result of our experiments, we are inclined to think, that in steel the charcoal assumes a crystalline form and arrangement.

The diamond is a gem characterised by its extreme hardness ; notwithstanding this, it often presents, in its rough state, sufficient evidence of having undergone abrasion by friction. There is a peculiar and almost indescribable grating sound produced by rubbing two diamonds together in the hand, which is a tolerably good test.

The diamond is sometimes externally, and always internally, bright, and causes a single refraction of the rays of light.
It is generally crystallized of various forms, of a lamellar structure, strikes fire with steel, and is the hardest of all known bodies; it cuts the hardest crystals, even rubies and sapphires, and the oriental amethyst.
Nothing but diamond powder, obtained by rubbing two diamonds against each other, can polish it, and it is cut by fragments of diamond set in a maule. The diamond is stated to be consumed and volatilized at a temperature which melts silver. It requires a temperature of 5000° F. for its combustion. When exposed to the sunbeam, and carried afterwards into darkness, it exhibits phosphorescence, and it has been stated that such diamonds as do not display this peculiarity may be made to do so by dipping them into melted borax. It becomes phosphorescent also when fixed to the prime conductor of an electrical machine, and a few sparks are taken from it.

The diamond becomes electric by friction, and the Honourable Mr.Boyle obtained electric gleams on rubbing two diamonds together in the dark. It is said, that when fulminating silver is exploded in contact with the diamond, reduced silver is precipitated on it. By igniting fulminating mercury both on and near some diamonds, I found however only faint and equivocal evidence of reduction. The specific gravity of the diamond has been estimated at 3500, water being 1000,—though it must be admitted, that the comparative hardness and specific gravity have been variously estimated, thus:

—An oriental diamond from Ormus, possessed a specific gravity of 3′ 4, and a comparative hardness equal to 20
—a pink diamond with a similar specific gravity, exhibited a hardness equal to 19
—while a bluish diamond, and one of a yellowish tint, with a similar hardness of 19, possessed a specific gravity of 3′ 3, and a cubic diamond of 18, a specific gravity of 3′ 2.