Solutions of Copal for Varnijhes. ' 34^ 



expofing them to dry in the fun and before the fire, and when dry, wafhed them with a 

 fponge and water ; but it fhewed no tendency to dilTolve ; though while in a liquid ftate it 

 feemed to poflefs all the properties of a gum. 



*As the procefies by which I diffolved the amber and copal to make the oil varniflies are to 

 be found in many books, and as it will be better for artifts to purchafe than attempt to make 

 thofe varnifhcs, it can fcarcejy be thought neceffary td detail thofe proceffes here ; but as I 

 believe the methods by which I diflblved the copal in fpirit of turpentine and fpirit of wine 

 «re not IcHOWn, I fliall now fubjoin them. , 



To dtffohe Copal in Spirit of Turpentine. 

 N.B. Whatever quantity is to be diflblved fliould be put into a glafs veffel, capble of 

 containing at leaft four times as much, and it fhould be high in proportion to its breadth. 



Reduce two ounces of copal to fmall pieces, and put them into a proper veffel. Mix a pint 

 of fpirit of turpentine with one-eighth of fpirit of fal ammoniac ; fliake them well together ; 

 put them to the copal, cork the glafs, and tie it over with a ftring or wire, making a fmall 

 hole through the cork. Set the glafs in a fand-heat, fo regulated as to make the contents 

 boil as quickly as poffible, but fo gently that the bubbles may be counted as they rife from 

 the bottom. The fame heat muft be kept up exadly, till the folution is complete. 



It requires the moft accurate attention to fucceed in this operation. After the fpirits are 

 mixed, they ftiould be put to the copal, and the neceflary degree of heat be given as foon a* 

 poffible. It fhould likewife be kept up with the utmofl regularity. If the heat abates, or 

 if the fpirits boil quicker than is directed, the folution will immediately ftop, and it will af- 

 terwards be in vain to proceed with the fame materials ; but if properly managed, the fpirit 

 of fal armoniac will be feen gradually to defcend from the mixture, and attack the copal, 

 which fwells and diflblves, except a very fmall quantity which remains undiffolved. 



It is of much confequencc that the veflel (hould not be opened, till fome time after it has 

 been perfectly cold. It has twice happened to me on uncorking the veffel, when it was not 

 warm enough to afFe£t the hand, that the whole of the contents were blown with vioknce 

 againft the cieling. It is likewife important that the fpirit of turpentine (houFd be of the 

 bed quality. I have never fucceeded with that which is fold at the colour-fhops } but 

 whenever I procured my fpirits at Apothecaries-hall, I have diflblved tht copal by the pro- 

 cefs I have defcribed without difficulty. 



This varnifh is of a rich deep colour when viewed in the bottle, but feems to give no co- 

 lour to the pidtures it is laid on ; if left in the damp, it remains facky, as it is called, a long 

 time ; but if kept in a warm room, or placed in the fun, it dries as well as any other turpen- 

 tine- varnifh } and when dry, it appears to be as durable as any other iblution of copal. 



To dijfolve Copal in Alcohol, 



Diffolvc half an ounce of camphor in a pint of alcohol ; put it in a circulating glafs, and 

 add four ounces of copal in fnoall pieces ; fet it in a (and-heat, fo regulated that the bubblet 



may 



