DIAMOND.

397

diamonds are never used. The inclination to be given to a set diamond in cutting glassis comprised within very narrow limits; and it ought, moreover, to be moved in thedirection of one of its angles. The curvilinear edge adjoining the curved faces, enteringas a wedge into the furrow opened up by itself, thus tends to separate the parts of theglass; and in order that the crack which causes the separation of the vitreous particleslna y take place, the diamond must be held almost perpendicular to the surface of theglass. The Doctor proved this theory by an experiment. If, by suitable cutting with thewheel, we make the edges of a spinel ruby, or corundum-telesie (sapphire) curvilinear,a ad the adjacent faces curved, these stones will cut glass as well as a glazier’s diamond, butbeing less hard than it, they will not preserve this property so long. He found that upon?tvmg the surface of even a fragment of flint the same shape as that of the cuitingdiamond, it acquired the same property; but, from its relative softness, was of little dura-ti°n. The depth to which the fissure caused by the glazier’s diamond penetrates, doesseem to exceed the two-hundredth of an inch.

I shall here introduce Mr. Milburn’s valuable observations on the choice of rough^amonds, as published in his work on Oriental Commerce .

.The color should be perfectly crystalline, resembling a drop of clear spring water, in thefiddle of which yon will perceive: a strong light, playing with a great deal of spirit. If“ e coat be smooth and bright, with a little tincture of green in it, it is not the worse,n d seldom proves bad, but if there is a mixture of yellow with green, then beware of it;ls a soft greasy stone, and will prove bad.

l he stone has a rough coat, so that you can hardly see through it, and thetoat be. bite and look as if it were rough by art, and clear of flaws or veins, and no blemish cast? the body of the stone (which may be discovered by holding it against the light), the°ne will prove good.

UnVi°** ten happens that a stone will appear of a reddish hue on the outward coat, notth co * or ™sty iron, yet by looking through it against the light, you may observe

it > l h e stone to be white (and if there be any black spots, or flaws, or veins in’bey may be discovered by a true eye, although the coat of the stone be the same), andb stones are generally good and clear.

i n r ? diamond appears of a greenish bright coat, resembling a piece of green glass,hti t0 black, it generally proves hard, and seldom bad; such stones have been' Vn to have been of the first water, and seldom worse than the second; but if anyst 0n Ule yellow seems to be mixed with it, you may depend on its being a very bad

All

to a 1 stones of a milky cast, whether the coat be bright or dull, if ever so little incliningtoouJi, s '* cast > are naturally soft, and in danger of being flawed in the cutting; andao c j th ey should have the good fortune to escape, yet they will prove dead and milky,to no account.

a u t[ j diamonds of cinnamon color are dubious; but if of a bright coat mixed withYou w n reen ’ ** len ^ le y are certainly bad, and are accounted among the worst of colors,this s 1 * ? leet w ith a great many diamonds of a rough cinnamon-colored coat, opaque;

hitt > 1 ls generally very hard, and, when cut, contain a great deal of life and spirit;°f a g co ' or is very uncertain ; it is sometimes white, sometimes brown, and sometimesVet arg e yellow. Rough diamonds are frequently beamy , that is, look fair to the eye,?'atno n( ] SO °f veins to the centre, that no art or labor can polish them. A goodit shoupi never contain small spots of a white or gray color of a nebulous form;

SlJ rfac» a . i' ree from small reddish and brownish grains, that sometimes occur on theircleav a J e ° r - m l heir interior. A good diamond should split readily in the direction of theCr ystak ’ .sometimes happens, however, that the folia are curved, as is the case in twin°f iaf e rj or ^ j etl tll * s happens, the stone does not readily cut and polish, and is therefore

‘he breadth 1 a ? d P ol *shed gem, the thickness must always bear a certain proportion to^ re > and must not be too thin nor thick; for, when too thin, it loses much of its

The term PearS “ 0t ualike S lass -

*f'f r ythin a cara [ * s sa id to be derived from the name of a bean, the produce of a speciesit h tre e is' <■ p a mL 6 tke district of Shangallas, in Africa ; a famous mart of gold-dust.1 “ears f} ow a ^ kuara , a word signifying sun in the language of the country; becauseJjjfcly Uruf or erS a . °f a flame color. As the dry seeds of this pod are always ofpi 16 beans we* wei ° kt > the savages have used them from time immemorial to weigh gold,d ther e f or ,„ e - , ans P°rted into India , at an ancient period, and have been long employ-J'ty 'veight ■ l: diamonds. The carat of the civilized world is, in fact, an imagi-arc ); it r i fM ■ Hslst * a S °f 4 nominal grains, a little lighter than 4 grains troy (poids de. In Valnj n „ rCS . carat = ra ins and to equipose 72 of the other.

- ? ^Pidary's 3 diamond, we must reckon that one half of its weight has been lost in

dnlate it s p i„ „ , s ’ whence its weight in this state should be doubled before wenv the general rule for estimating diamonds. The French multiply