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on a steel plate revolving with great ve- would be a matter of great difficulty ; locity-an operation perfectly analogous while the attempt to make such a figure to that of glass cutting, or the ordinary practically, by any one unskilled in the well-known lapidary's wheel. The cutting operation, would only lead to continual plates are usually about ten or twelve in- trial—and error-attempts, which, even ches in diameter; they are placed horizon- if the thing were ever properly done at tally with their spindles vertical, and all, would waste a large portion in the are made to revolve about thirty or forty operation, and consequently much dimitimes in a second; the part acting on nish the ultimate available size. Any one the diamond travelling over the facet who will try, for example, to cut a turnip at the rate of about a mile in a minute. or a potato, by his eye and hand only, Diamond powder, of extreme fineness, into a regular octohedron, or solid figure mixed with the best olive oil, is placed of eight equal and similar sides, will at with a feather upon the upper table of once appreciate the difficulty. Yet the the wheel, and the apparatus is then diamond-cutter has to do a much more ready for action on the diamond. The difficult problem, namely, to give about stone is embedded in a mass of soft sixty symmetrical and regular faces to metal, an amalgam of lead and tin, easily stones sometimes only about an eighth of fusible, and yet hard enough to retain an inch diameter; without any mechanthe stone firmly in its position ; this is ical aids whatever to his judgment; and fixed in a moveable handle, which is yet producing, without a particle of unagain attached to a small frame. The necessary waste, the very largest stone workman, having first heated the metal geometrically possible out of the rough to a soft state, beds the diamond in it in body. This of course can only be the the required position, and fixes it there result of great skill and long experience. by plunging into water; the frame is Having made one facet, he judges by then placed to project over the wheel, his eye the exact angle at which the and the diamond, being downwards, stone must be placed to cut the new one, comes in contact with its upper surface, and the exact depth to which the grinding on which the diamond powder is placed ; for the latter must be carried ; and weights are then applied, and the result accurately is this done, that it is very of the friction, at the immense velocity, seldom a good workman ever has to is to cut a facet upon the stone in a very revert to a facet for correction, after he short space of time. When one of these has once passed it over.
The stone is is finished, the workman softens the so fixed in the metal as to leave other metal, extracts the stone, and replaces it facets visible for constant comparison in the proper position for making another with the one under progress; and the facet; and here comes into play a very handle is capable, by a sort of universal remarkable feature of the operation, joint, of adjustment to any nicety for the namely, the accuracy of judgment which position of the stone in touching the skill and experience give in arranging wheel. There is no further division of the faces of the stone. It is obvious labour than between the rough cutter that, in any many-sided solid body whose and the finisher—the latter taking the shape is to have any pretensions to stone from the former in its roughed-out regularity or symmetry, the different state, and returning it to the proprietor faces must not only all stand in certain in the shape of the perfect finished brildefinite angular positions in regard to liant ready for sale. The last touches to each other, but must all bear a certain the facets consist of polishing, or giving size in relation to the magnitude and to them the peculiar diamond lustre; form of the whole. Further, any one but this is in no wise different from the acquainted with geometry will know, grinding, except in being done with that for a solid figure of fifty or sixty more care. The man can at any time sides, the determination of these angles adjust the weight or force with which
he can remove it entirely, and substi- a pointed apex.
The flat base is imtute the gentle pressure of his hand; bedded in the setting ; and, therefore, in and he can also modify the velocity of the rose diamond, the whole of the the grinding action ; for, although the stone appears projecting above. wheel itself is kept at a constant number The brilliant is the more valuable of revolutions per minute, he can place form ; it may be considered as formed the stone nearer to, or further from the of two pyramids, connected together at axis, as he likes, which will of course their bases, with the apex of each give a less or greater effective velocity, truncated or cut off, and the sides according to the radius of the acting worked into facets, as in the case of the circle.
The stone is held in the setting The diamond powder, of which a large at the broadest part, or junction of the quantity is used, is obtained partly from pyramids ; one pyramid projects upthe first process, of rough-cutting the wards in sight, the other is hidden stones; partiy from diamonds of a quality below, so that only half the stone, or not good enough to cut for sale, which somewhat less, appears; but the hidden are broken up for the purpose ; and partly part is most powerfully effective in adfrom the newly discovered substance, ding to the brilliancy. The apex of "carbonado,” which is hard enough for the upper pyramid is cut off to a conthis use, although of a somewhat coarse siderable extent, and the large facet thus quality. The powder is carefully sifted, formed is called the table : the correcleaned from dirt and extraneous mat- sponding facet below, formed by the ters, and, when about to be used, is mixed truncation of the lower
or hidden with the finest vegetable oil.
pyramid, is much smaller, and is called The workmen are all Jews, and are the collet. The rim where the setting regularly educated to the trade. They takes hold, or, as we have described it, are paid by piece-work. Formerly, they the junction of the bases of the pyramids, did their work at their own houses, their is called the girdle. There are thirtywheels being turned by manual power; two facets cut round the upper slanting but it is now found more advantageous surface of the stone, i.e., between the for the large proprietors to provide girdle and the table, and twenty-four workshops of their own furnished with on the lower part, between the girdle steam power, for the use of which the and the collet. All these facets have men pay out of their earnings. Some of names by which they are known to the the more skilful and industrious men cutters ; and all the dimensions of the realise considerable incomes. There is, stone should, in order to produce the of course, always temptation to dis- best effect, bear certain definite proporhonesty, from the great value which is tions to each other. The most favourcompressed into so small a space; but all able form of brilliant for exhibiting the possible precautions are taken, and the lustre of the stone is considered to be character of the men is made of so high a square, having the corners slightly weight in all the transactions with them, rounded off ; but, of course, many stones that losses very seldom occur.
will not admit of being cut to this form The form into which a diamond is without loss, and, therefore round, oval, cut has great influence on its beauty and pear shapes, &c., are perhaps more fire. The two most common are what
The stones lose about fifty are called the “brilliant,” and the per cent. in cutting, more or less, so “rose” or “rosette.” The latter, so that, to make a brilliant of one carat, a named from its similarity to an un- rough stone of two carats is required. opened rosebud, was one of the earliest The chemical nature of the diamond forms in use, and is applied generally is well known. It consists of pure to the cheaper kinds of stones.
carbon ; identically the same thing as sort of pyramid, with a flat base, and the soot from a kitchen chimney, but in inclined facets, terminating upwards in
It is a
different form. Sir Isaac Newton sus
pected, by its optical properties, that it mond, therefore, as far as destructibility was a combustible body; and its cha- by abrasion is concerned, defies all racter has been subsequently proved nature. This quality renders it of conbeyond a doubt. If sufficient heat be siderable value for other purposes than applied, diamonds will completely con- ornament—as for cutting glass, and for sume, combining with oxygen to form working other stones, for the pivots of carbonic acid, precisely like charcoal or watch-work, &c. coke in an ordinary furnace.
But, although the diamond is so hard, There have been many speculations it is very easily broken, and, indeed, by as to the mode by which nature has a particular knack, it may even be cut effected this wonderful metamorphosis, with a common pen-knife. This appaand many have been the attempts made rent anomaly is due to what is called to imitate her; but hitherto she has its cleavage, a result of the crystalline kept her secret well, and baffled all her structure. Many well-known substances, admiring followers. Sir David Brew- as slate for example, split or cleave with ster has suspected, by optical peculiari- peculiar facility in certain definite dities exhibited in some examples, that rections, while they offer considerable rediamonds may not be of mineral origin, sistance to fracture in all others. The but may have resulted from the harden- diamond has this property, cleaving ing of a kind of gum, something like easily in no less than four directions, amber.
parallel to the surfaces of the original A curious substance has lately been octohedric crystal ; and, therefore, when found in the Brazilian mines, called moderate force is applied in either “Carbonado," or amorphous diamond-a of these ways, the stone splits into kind of intermediate grade between pieces. Pliny, mentioning the great diamond and charcoal, combining the hardness of the diamond, states that if hardness of the former with the black laid upon an anvil, and struck with a unformed character of the latter. Close hammer, the steel would sooner give inspection shows curious traces of a pas- way than the stone. This assertion is a sage between the two states; and it is matter of popular belief in the present thought further examination of this day, but we would not recommend any substance may lead to some better in- possessor of a good diamond to try the sight than we at present possess, as to experiment. The chances of some of the chemical nature of the change. the forces acting in the cleavage direc
The diamond is totally insensible to tions are so great, that the stone would the action of any chemical reagents. Its in all probability fly to pieces under the specific gravity is about 3.5.
first blow. The truth is, that Pliny The most characteristic quality of the referred not to the diamond, but to the diamond is its extreme hardness ; it is sapphire, which, though less hard than the hardest substance known. This the diamond, cleaves only in one direcquality was the earliest that attracted tion, and might, therefore, withstand attention, the name being derived from the test named. the Greek 'Adáuas, i.e. incapable of being The cleaving property of the diamond crushed or subdued for the comparison is made useful in two ways in the manuof hardness in different degrees, mine- facture : first, by splitting the stones ralogists have adopted a scale repre- when they contain flaws, and secondly, sented by the following substances. 1, in the preparation of diamond powder. talc ; 2, gypsum ; 3, calcareous spar; 4, When a rough diamond is seen to contain fluor spar; 5, phosphate of lime; 6, a defect of sufficient extent to depreciate felspar; 7, quartz ; 8, topaz ; 9, sap- its value as a single gem, it is split in phire and ruby ; 10, diamond. Any two, precisely at the flaw, so as to make one of these substances will scratch all two sound stones. This is a very below it in the scale, and may be simple operation in appearance, done in amount of skill to do it properly. The well-known prismatic colours. The cut workman, by a sort of intuitive know- drops of glass chandeliers show a familedge, gained by long experience, knows, liar example of these properties. Now, on a careful inspection of the stone, the the degree in which this effect is proexact direction which a cleavage plane duced by any substance depends on the passing through the flaw will take. refractive power it possesses, and it so Tracing this plane therefore to the exte- happens that the diamond has this rior, he makes on the edge of the stone, power in an extraordinarily high degree, precisely in that spot, a slight nick with its index of refraction being 2:47, while another diamond. He then places a small that of glass, or rock crystal, is only knife in that nick, gives it a light tap about 1.6, and of water 1.3. The with a hammer, and the stone at once effect of this great refractive capability, cleaves in two, directly through the particularly when aided by judicious flaw. This operation, in daily practice cutting, is, instead of allowing the light in the Amsterdam works, is one of the to pass through, to throw it about, backmost elegant and instructive processes wards and forwards in the body of the in the whole range of mineralogy. It stone, and ultimately to dart it out again is reported that Dr. Wollaston, cele- in all sorts of directions, and in the most brated as almost the originator of the brilliant array of mingled colours; and science of crystallography, once made a this is this marvellous effect that meets handsome sum by purchasing a large the eye. Sir David Brewster has shown flawed diamond from Rundall and that the play of colours is enhanced by Bridge at a low price, and subsequently the small dispersive power of the diasplitting it into smaller sound and
mond, in comparison with its refractive valuable stones; the principle of the properties. operation not being then generally It is often supposed that diamonds known.
are essentially colourless, but this is a Another use of the cleavage principle mistake ; they exist of many colours, is in the preparation of diamond powder
. yellow, orange, pink, blue, green, brown, Small diamonds of inferior quality, are and black. Three-fourths of the stones put into a steel mortar, and pounded found are tinged with some colour or and rubbed with a steel pestle, when other, mostly pale yellow, or yellow they break up through their various brown. The perfectly pure and colourcleavage planes into still smaller pieces, less ones are selected as the most valuand at last rub themselves into the able for the general market; but it finest dust, fit for use on the wheel. sometimes happens that fine stones of a The cause of the wonderful brilliancy decided colour are
more prized than of the diamond is not popularly known. white, from their peculiar rarity and It has no inherent luminous power; it beauty:? A blue diamond of about fiftyis simply transparent, like common glass, six carats, belonging to Mr. Hope, is a and yet, if the latter were cut into the celebrated stone, combining the beautiform of a brilliant, it could no more be ful colour of the sapphire with the fire mistaken for a real one than for a sap- and brilliancy of the diamond. phire or an emerald. The secret, there- The quality of diamonds depends upon fore, of the brilliancy of the diamond their colour, purity, transparency, and must lie in something other than its freedom from flaws. Stones perfectly clearness or its transparency. It is
It is colourless, pure, clear, and free from all owing to its great refractive power. defects, are said to be of “the first When rays of white light pass through water;" if they have slight imperfectransparent substances they are tions, they are of the second water;" fracted, or bent out of their former
1 North British Review, Nov. 1852. course, and under certain circumstances
2 A fine collection of coloured diamonds, beare separated into their constituent ele
longing to Mr. Tennant, are now exhibiting at ments, and dispersed in the form of the the Kensington Museum.
and, if tinged with colour, or otherwise This rule will, however, hold only up very defective, of “the third water." to the limit of stones in ordinary sale.
The value is estimated according to Such as are very large and of exceptional the weight, which is expressed in carats; production cannot be valued by any one carat being about 205 French milli- rule ; they are worth just what the state grammes, or 3 grains troy.
of the demand among crowned heads and For small stones, not exceeding one millionaires will enable their holders to carat in weight, the value may be as- get for them. sumed approximately to be proportional The general value of diamonds has to the weight; but, as the stones increase been rising of late years; for, though the in size, this rule does not apply—the production is not scanty, the demand, larger ones being more rare, and there- owing to general prosperity, and the fore having a value greater than is due extension of ornament to wider classes to their mere size. To provide for this, in society, is largely on the increase. it is generally assumed that, above one Imitations of diamonds are generally carat, the value shall increase as the of one of the following three kinds : square of the weight-i.l., that a stone 1. White Topaz.—This is nearly as double the weight of another shall have 'hard as diamond, and about the same four times the value ; treble the weight, specific gravity, and may therefore be nine times the value ; ten times the mistaken for it when tried by these weight, one hundred times the value, tests. A London jeweller died lately in and so on.
the belief that a fine stone he had come The money value of diamonds is a into the possession of was a valuable difficult subject to touch upon, as diamond, and left large legacies to be distinction must always be drawn be- paid out of the proceeds of its sale; but tween the retail price asked by jewellers it proved, on examination, to be only a from the public, and the real market white topaz, and of very little value. price of the diamonds as sold by the The difference may be recognised by the dealers. Moreover, the value will al- optical qualities, which differ much in ways vary according to the state of the the two stones. market, as well as according to the 2. Rock Crystal (Brighton diamonds, quality and cut of the stones. Irish diamonds, &c.).—This substance, rough approximation, brilliants of first- though hard enough to scratch glass, is rate quality, and perfect in every respect, much softer than diamond, and is easily may be estimated at about 121. per scratched by it. It is also much inferior carat ; reducible to half this, or even in brilliancy and in specific gravity. less, for stones of inferior water. Ac- 3. Paste.--This, which is a glass cording, therefore, to the rule of the prepared with metallic oxides, can be weight above laid down, a diamond of made equal to diamond in refractive half a carat might be estimated as worth power, and therefore can be given a 61. ; but one of two carats would be great brilliancy; but it is very soft, worth 2 x 2 x 12 = 481; one of five softer even than common glass, and it carats 5 x 5 x 12 = 3001; and so on.1 does not retain its lustre. 1 Referring to the square' or best form of
There is also a method of deception brilliants, the solid content of a cut stone, of sometimes practised by what is called proper proportions, is about of that of the
half-brilliants ; i. e. stones in the form circumscribing parallelopipedon ; and, taking
d3 the Sp. gr. at 3:5, we shall obtain the following rule. Let d = side of the square, or breadth
Weight = 12.5
125' across the girdle, and t = the thickness of the
d6 stone, from table to collet; both in tenths of
or the value in £
so that the
13 to 30, an inch ;-then
worth of stones varies, cæteris paribus, as the d? Weight in carats =
sixth power of their lineal dimensions. The 8:3
height of the table above the girdle should be In a well proportioned stone t should be = $t;- the depth of the collet below = s t. =jd, and the rule thus becomes
The breadth across the table should be