Jar ihe Vfe of Artijls, Manufa&urers, &c.' lit 



bark of the birch-tree in fuch a manner that water cannot 

 touch them, and place them thus covered into a pot of boil- 

 ing water, with a ftone above them to keep them at the bot- 

 tom. When they have boiled about an hour they take them 

 from the bladder or bark, and they are then found to be foft 

 and vifcous. In this Itale they employ them for glueing 

 together the two pieces of their bows, which they iLron^ly 

 comprefs and tie up until the clue is well dried. Thele pieces 

 never afterwards feparate. — TraiifaSiions of the Academy of 

 Sciences at Stcckholm. 



XIV. JeiueJlers Ceinent. 



In fetting precious ftones, pieces ai e fometlmcs broken off" 

 by accident. In fuch cafes they often join the pieces fo cor- 

 re£lly, that an inexperienced eye cannot difcover the ftone to 

 have been broken. They employ for this purpofe a fmall 

 piece of gum-niallic applied between the fragments, which 

 are previoufly heated fuflicicntly to enable them to melt the 

 interpofed gum. They are then preflcd together to force out 

 the redundant quantity of gum. 



In the fame manner cameo heads, but without any ground, 

 made of palle (white enamel or coloured glafs) are often ce- 

 mented on a piece of real ftone to fcrve tliem for a ground, 

 producing the appearance of a real onyx, from which they 

 can with difficulty be fometimcs diftingui(hed. 



Backs are alfo cemented to ftones in the fame manner, to 

 change their hue. That is, behind a tranfparent ftone the 

 colour of which is wiflied to be altered, a thin plate of a 

 ft^one of a different colour is cemented, which alters the co- 

 lour of the refraded light to a mixed tint partaking of that of 

 both. In this cafe, the furfaces to be joined are^previoufly 

 ground as flat and true as polfible. They are called doullets. 



XV. Tiirhey Cemejit for joining Metals, Glafs, ^c. 



The jewellers in Turkey, who are nioftly Armenians, have 

 a curious metliod of ornamenting watch-cafes, and fimilar 

 things, with diamonds and other ftones, by fimjily glueino- 

 them on. The ftone is fet in filver or gold, and the lower 

 part of the metal made Hat, or to corrcfpond with the part to 

 which it is to be fixed; il is then warmed gently, and the 

 glue applied, which is fo very ftrong that the parts never fe- 

 parate. 'Jhis glue, which may be applied to many pinpofes, 

 as it will ftrongly join bits of glafs or polifticd ftcel, is thus 

 made: 



Difiolvc five or fix bits of maftic, as large as pe.is, in as 

 much fpirit of wine as will fafiicc to render ii licjuid; in an- 



oilier 



