DIAMOND. 



723 



Different 

 lsirms into 

 which they 

 are cut. 



Diamond, en bench or table that supports the plate, and pressing 

 —~Y~~" 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. A little oil and diamond powder is now dropped 

 on the plate ; it is set hi motion at the rate of about 200 

 revolutions in a minute, and the grinding and polishing 

 processes now begin. The diamond is 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 considerable, and sometimes increases to such 

 a degree as to soften the solder, and displace the dia- 

 mond. This accident sometimes occasions a flaw in the 

 diamond, and always damages the skive, by tearing up 

 its surface. There is room in the skive for three or four 

 diamonds, and a skilful operator can undertake the 

 polishing of all of them at the same time. The com- 

 pletion of a single facet often occupies some hours. 



Diamonds are cut and manufactured by jewellers 

 into brilliant, rose, and table diamonds. To fashion a 

 rough diamond into a brilliant, the first step is to mo- 

 dify the faces of the original octahedron, so that the 

 plane formed by the junction of the two pyramids shall 

 be an exact square, and the axis of the crystal precisely 

 twice the length of one of the sides of the square. The 

 octahedron being thus rectified, a section is to be made 

 parallel to the common base, or girdle, so as to cut off 

 •j^ths of the whole height from the upper pyramid; 

 and -rg-th from the lower. The superior and larger 

 plane thus produced, is called the table, and the inferior 

 and smaller one is named the collet ; in this state it is 

 called a complete square table diamond. To convert it 

 into a brilliant, two triangular facets are placed on 

 each side of the table, thus changing it from a square 

 into an octagon ; a lozenge -shaped facet is also placed 

 at each of the four corners of the table, and another 

 lozenge extending lengthwise along the whole of each 

 side of the original square of the table, which, with two 

 triangular facets, set on the base of each lozenge, com- 

 plete the whole number of facets on the table side of 

 the diamond, viz. eight lozenges, and twenty-four tri- 

 angles. On the collet side are formed four irregular 

 pentagons, alternating with as many irregular lozen- 

 ges, radiating from the collet as a centre, and bordered 

 by 16 triangular facets adjoining to the girdle. The 

 brilliant being thus completed, is set with the table 

 side upwards, and the collet side implanted in the ca- 

 vity made to receive the diamond. Such is the method 

 recommended by Mr Jeffries for cutting the brilliant 

 diamond, and which ought to be attended to, if we are 

 desirous that the diamond should display its highest 

 degree of lustre and play of colour ; but Mr Mawe re- 

 marks, " that so great a stress is laid by modern fa- 

 shion on the superficial extent of a brilliant, that the 

 rules just given are not much attended to; and, in 

 forming the facets, artists trust principally to an accu- 

 rate and well practised eye. * 



The regular rose diamond is that form given to 

 those stones, the spread of which is too great in pro- 

 portion to their depth, to admit of being brilliant cut, 

 without a great loss of substance. It is formed by in- 

 scribing a regular octagon in the centre of the table 

 side of the stone, and bordering it by eight right angled 

 triangles, the bases of which correspond with the sides 



of the octagon ; beyond these is a chain of eight trapezi- Diamond, 

 urns, and another of sixteen triangles. The collet side """ ~Y~~' 

 also consists of a minute central octagon, from every 

 angle of which proceeds a ray to the edge of the girdle, 

 forming the whole surface into eight trapeziums, each 

 of which is again subdivided by a salient angle (the 

 apex of which touches the girdle,) into one irregular 

 pentagon, and two triangles, t 



The table diamond is the least beautiful mode of cut- 

 ting, and is used only for those stones, or rather frag- 

 ments, which, with a considerable breadth, have only 

 a very trifling depth. 



In valuing diamonds, we have to attend to their Valuing 

 weight, their form when cut, colour, transparency, purity, diamonds. 

 or freedom from Jlaivs, veins and stains, the regularity of 

 the cleavage, proportion of the parts, and lastly, the set~ 

 ting on of the facets. 



In the cutting either of a brilliant or a rose diamond, l. Weight 

 of regular proportions, so much is cut away, that the and form. 

 weight of the polished gem is not more than half that 

 of the rough crystal out of which it was formed; whence 

 the value of a cut diamond is esteemed equal to that of 

 a similar rough diamond of twice its weight, exclusive 

 of the cost of workmanship. The weight, and conse- 

 quently the value, of diamonds, is estimated in carats, 

 one of which is equal to four grains, and the difference 

 between the price of one diamond and another, cceteris 

 paribus, is as the square of the respective weights. 

 Thus the value of three diamonds, of one, two, and 

 three carats weight, is as one, four, and nine. The ave- 

 rage price of rough diamonds^ that are worth working, 

 is about L. 2 for the first carat ; and consequently 

 in wrought diamonds, exclusive of the cost of work- 

 manship, the cost of the first carat is L. 8. In other 

 words, in . order to ascertain the value of a wrought 

 diamond, ascertain its weight in carats, and fractions 

 of a carat, multiply this by two, then multiply this pro- 

 duct into itself, and finally multiply this latter sum by 

 L, 2. Hence a wrought diamond of 



1 carat is worth L.8 



2 32 



3 72 



4 128 



5 200 



6 288 



7 392 



8 512 



9 612 



10 800 



20 3,200 



30 7,200 



40 12,000 



50 20,000 



60 28,800 



70 39,200 



SO 51,200 



90 64,800 



100 80,000 



This rule, however, actually holds good only in the 

 smaller diamonds of. 20 carats and under ; the larger 

 ones, in consequence of the scarcity of purchasers, be- 

 ing disposed of at prices greatly inferior to their esti- 

 mated worth. The value of some of the most perfect 



" The brilliant form was invented in England. 



■f The finest rose cut diamonds were formerly manufactured in Hjlland. 

 known and practised at Antwerp. 



More than 300 years ago, this mode of cutting wits 



