24 DIAMOND 



Diamonds possessed of no extraordinary magnitude, but of a good form and a 

 pure water, may bo valued by a certain standard rule. In a brilliant, or rose diamond 

 of regular proportions, so much is cut away that the weight of the polished gem does 

 not exceed one-half the weight of the diamond in the rough state ; whence the value of 

 a cut diamond is esteemed equal to that of a similar rough diamond of double weight 

 exclusive of the cost of workmanship. The weight and value of diamonds are reckoned 

 by carats of 4 grains each ; and the comparative valuo of two diamonds of equal 

 quality, but different weights, is as the squares of these weights respectively. The aver- 

 ago price of rough diamonds that are worth working, is about 21. for one of a single 

 carat ; but as a polished diamond of one carat must have taken one of two carats, its 

 price in the rough state is double the square of 21., or Si. Therefore to estimate the 

 value of a wrought diamond, ascertain its weight in carats, double that weight, and 

 multiply the square of this product by 21. Hence, a wrought diamond of 



1 carat is worth 8 7 carats is worth 392 



2 32 8 512 



3 ,. 72 9 612 



4 128 10 800 

 6 200 20 3,200; 

 6 288 



beyond which weight the price can no longer rise in this geometrical progression, from 

 the small number of purchasers of such expensive toys. A very trifling spot or flaw 

 of any kind lowers exceedingly the commercial value of a diamond. 



The preceding rule was given by Jefferies many years ago, and though no doubt 

 correct enough in its day, is of little or no value now. The following formula has 

 been recently given by Schrauf, of Vienna (Edelsteinkunde, 1869) : Let a be the weight 

 of a given stone in carats, and b the value of a diamond of one carat ; then the valuo 



of the stone of a carats is approximately ? (a + 2) b. 



After all, it may be doubted whether any really useful rule can be given to connect 

 weight with value ; certainly there is none applicable to large stones. The market 

 value is often capricious ; at one time, stones of a particular size will be fashionable, 

 and will therefore fetch unusually high prices. Moreover, much depends on the 

 quality or ' water ' of the gem ; if the stone be ' off-coloured,' or if it contain cloudy im- 

 perfections known in the trade as ' milk ' or ' salt,' its value is very greatly diminished. 

 On the other hand, brilliantly-coloured diamonds are prized as ' fancy stones,' and are 

 eagerly purchased at high prices. 



Diamonds are used not only as decorative gems, but for more useful purposes, as for 

 cutting glass by the glazier, and all kinds of hard stones by the lapidary. 



On the structure of the glaziers' diamond we possess some very interesting obser- 

 vations and reflections by Dr. Wollaston. He remarks, that the hardest substances 

 brought to a sharp point scratch glass, indeed, but do not cut it, and that diamonds 

 alone possess that property ; which he ascribes to the peculiarity of its crystallisation 

 in rounded faces, and curvilinear edges. For glass-cutting, those rough diamonds are 

 always selected which are sharply crystallised, hence called diamond sparks ; but cut 

 diamonds are never used. The inclination to be given to a set diamond in cutting 

 glass is comprised within very narrow limits ; and it ought, moreover, to be moved 

 in the direction of one of its angles. The curvilinear edge adjoining the curved faces, 

 entering as a wedge into the furrow opened up by itself, thus tends to separate the 

 parts of the glass ; and in order that the crack which causes the separation of the 

 vitreous particles may take place, the diamond must be held almost perpendicular to 

 the surface of the glass. The Doctor proved this theory by an experiment. If, by 

 suitable cutting with the wheel, we make the edges of a spinel, ruby, or corundum- 

 telesie (sapphire), curvilinear, and the adjacent faces curved, these stones will cut glass 

 as well as a glaziers' diamond, but being less hard than it, they will not preserve this 

 property so long. He found that upon giving the surface of even a fragment of flint 

 the same shape as that of the cutting diamond, it acquired tho same property ; but, 

 from its relative softness, was of little duration. The depth to whu-h tin 

 caused by the glaziers' diamond penetrates does not seem to exceed the two-hundredth 

 of an inch. 



The following remarks by Mr. Tcnnant cannot fail to bo of interest, and, as pointing 

 out the errors which have been frequently committed through ignorance, are of great 

 value : 



'By attending to the forms of the crystal, we arc quite sure that we shall not find 

 the emerald, sapphire, zircon, or topaz in the form of a cube, octahedron, tetrahedron, 

 or rhombic dodecahedron; nor the diamond, spinel, or garnet in that of a six-sided 



