PEARLS, ARTIFICIAL 



519 



and varied forms found amongst real pearls. Gum, instead of wax, is now used 

 to fill them, by which they attain a high degree of transparency, and the glassy 

 appearance has been lately obviated by the use of the vapour of hydrofluoric acid. 

 This acts in such a manner as to deaden the surface, and remove its otherwise glaring 

 look. 



The material out of which these beads are formed is small glass tubing, like that 

 with which thermometers are made. The tubes for the bright-red pearls consist of 

 two layers of glass, a white opaque one internally, and a red one externally ; drawn 

 from a ball of white enamel, coated in the Bohemian method with ruby-coloured glass, 

 either by clipping the white ball into a pot of red glass, and thus coating it, or by in- 

 troducing the ball of the former into a cylinder of the latter glass, and then cementing 

 them so soundly together as to prevent their separation in the subsequent pearl pro- 

 cesses. These tubes are drawn, in a gallery of the glasshouse, to 100 paces in 

 length, and cut into pieces about a foot long. These are afterwards subdivided into 

 cylindric portions, of equal length and diameter, preparatory to giving them the 

 spheroidal form. From 60 to 80 together are laid horizontally in a row upon a 

 sharp edge, and then cut quickly and dexterously at once by drawing a knife over 

 them. The broken fragments are separated from the regular pieces by a sieve. 

 These cylinder portions are rounded into the pearl shape by softening them by a suit- 

 able heat, and stirring them all the time. To prevent them from sticking together, 

 a mixture of gypsum and plumbago, or of ground clay and charcoal, is thrown in 

 among them. 



Figs. 1611 and 1612 represent an apparatus for rounding the beads : fig. 1611 is 

 a front view of the whole; fig. 1612 is a section through the middle of the former 

 figure, in the course of its operation. The brick furnace, strengthened with iron bands, 

 2, 3, 5, 7, 8, has in its interior (see fig. 1612) a nearly egg-shaped space, B, provided 

 with the following openings : beneath is the fire-hearth, c, with a round mouth, and 



opposite are the smoke flue and chimney, D ; in the slanting front of the furnace is 

 a large_ opening, E, fig. 1611. Beneath are two smaller oblong rectangular orifices, 

 F, G, which extend somewhat obliquely into the laboratory, B. H serves for introducing 

 the wood into the fireplace. All these four openings are, as shown in fig. 1612, 

 secured from injury by iron mouth-pieces. The wood is burned upon an iron or 

 clay bottom piece, r. A semi-circular cover, N, closes during the operation, the 

 large opening E, which at other times remains open. By means of a hook, in, and a 

 chain, which rests upon a hollow arch, h, the cover w is connected with the front 

 end of the long iron lever R, R'. A prop supports at once the turning axis of this 

 lever and the catch b, c ; the weight Q draws the arm H down, and thereby holds 

 up N : E therefore remains open. By rods on the back wall, T T, the hook i, in 



