GEMS; JEWELS. Besides mere purpo ses of ornament, the hard and beautiful stones or crystals which constitute gems are applied to many useful purposes.
The application of Gems in watches is noticed elsewhere [JEWELLING OF WATCHES.] A well-known application of the diamond is in cutting glass [DiAnosn]. Gems are occa sionally employed for the nibs of pens ; thus, pens made of gold, with small rubies at the nibs, have been known to bear constant use for many years without any appreciable wear ing. Many years ago Messrs. Hawkins and Mordan patented a new pen, of which the barrel was made of horn or tortoiseshell, and the nib of a small fragment of diamond or ruby, imbedded into the horn by pressure. From the high refractive power of the diamond, it is employed to form minute and exquisitely accurate lenses for the best kinds of micros cope ; Mr. Pritchard succeeded in forming such lenses, after the professed diamond makers had pronounced it to be impossible ; and Sir David Brewster has had similar lenses made of rubies and garnets. In respect to the general operations of the lapidary or jewel-cutter, they could hardly be conducted without the aid of diamond- dust ; for the general mode of cutting and shaping precious stones is to hold them against a very small metallic disc or wheel, which is rotating with great velocity, and to moisten the edge of this disc with oil and diamond dust ; the ex ceedingly hard particles of diamond enable the disc to cut the stone or jewel.
The manufacture of factitious or artificial gems is a very curious department of art. Any one who glances round a shop containing cheap jewellery, will at once see that no inconsider able portion of the glittering store is of this nature. Where pence instead of shillings are charged—or in some cases pence instead of pounds—it is easy to see that such must be the case. The brilliant transparency of the diamond, the purple of the ruby, the blue of the sapphire, the green of the emerald, the orange tint of the hyacinth, the transparent blood-red of the garnet, the variegated tints of agate and porphyry, the delicate subdued whiteness of the pearl — all are imitated.
Most of these imitative gems are made of glass, called paste in this country and strass in France; it is of this substance that most artificial diamonds are formed ; and by mixing various metallic oxides with the strass, the colours of other gems are imitated. The strass is not common glass, but is carefully made from a mixture of rock-crystal, potash, borax, and oxide of lead. The oxides of iron, antimony, arsenic, manganese, copper, chromium, cobalt, &c., are employed to give to the strass the requisite colour for other gems.
Many artificial gems are doublets, and deceive the eye by a curious contrivance. Two little fragments of glass, previously shaped, are cemented together with Venice turpentine and mastich, coloured with carmine, lake, Prussian blue, verdigris, or some other pigment; a humble sort of imitative gem is thus produced. A still humbler method, and the cheapest of all, consists in simply placing a bit of coloured metal foil behind the frag ment of transparent glass.
The manufacture of artificial pearls is more remarkable perhaps than that of any other gem. They are made of glass beads, coated on the inside with a peculiar substance. ,A fine and narrow glass tube is held in a lamp at one end, while the workman blows through it from the other ; the heated end is blown out into a globnlar form : and the workman breaks off the bead thus made and proceeds to form another. So rapidly is this done, that a workman can make 5000 or 6000 in a.: day. The pearl-liquor, or Essence d'Orient, is made by steeping in water the scales of the bleak or blay fish ; and a single drop is dexterously blown into every bead by means of a little tube ; the bead is shaken, to equalize the contact of the liquid with the interior surface. Each bead is then filled with wax, to strengthen it, and a hole is made through the wax to receive a string.—Artificial pearls are chiefly made in Paris.