ON CO^AL VAUVISHES. J55 



Junker infbrms' us that it readili/ fucceeds, iffpirit of faUammO" 

 Iliac, mixed with a due proportion of oil of Jpike or oil of tur- 

 pentine, be ufed as the menftruum." Upon this tint I pro- 

 ceeded till I had difcovered the procefs I have defcribed ; but, 

 though the varnifti anfwered every purpofe I could wifti, the 

 trouble of making it being great, and the /ailure of the procefs 

 fo frequent that I determined to feek for fome more convenient 

 method. 



Having found that copal, when powdered and rubbed in the Invention of 

 mortar with a fmall quantity of camphor, became foft, and in a ^gJJ^^ ^j^* 

 few minutes, united in one coherent mafs, I conjectured that by than aminonia. 

 means of camphor, copal might be diffolved in alcohol, and 

 upon trial found that it might be fo dilTolved, and rendered fit 

 for the purpofes of varnith ; this I did, not by way of experi- 

 ment, but in confiderable quantities and at various times ; fo 

 often, that I am authorifed to fay, that if the materials are 

 good, and the procefs I have defcribed in the Tranfaftions of 

 the Society for Encouragement of Arts be followed, there can 

 be no difficulty in making a colourlefs fpirit varnith from copal ; 

 and as a proof that this may be done, I fend you a fmall quan- 

 tity that I made fome time ago, and which will enable you to 

 judge whether it deferves to be "placed in the clafs of vamijkes.** 



But as it is improper, for many reafons, to varnifti pictures Sp. of turpen- 

 with any fubftance diffolved in alcohol, I tried to diffolve the ^j^^^iPJ^^J""'' 

 copal in fpirit of turpentine by the intervention of camphor, 

 and fucceeded ; not fo eafily indeed as in alcohol, but always 

 with the certainty of fuccefs, when the precautions I have de- / 

 fcribed were obferved; this has been uniformly the cafe with 

 myfelf for feveral years, as well as feveral artifts who have 

 made the trial ; and it has now been proved by many years ex- 

 perience that copal diffolved, by means of camphor, in fpirit of 

 turpentine, is as colourlefs as the refin itfelf and perhaps as jj^j^ ^j^r^j^ jg 

 durable, tince pictures that have been varniflied many years alfo excellent, 

 with it have been preferved without the leaft change even in 

 the colour of the varnifti, which would not have been the cafe 

 had any other fubftance been ufed. 



As Mr. Tingry's experitnents lead to very different conclu- 

 fions, I am compelled to fuppofe, either that they were inac- 

 curately made, or that the copal, camphor, alcohol, and* 



fpirit 



* Mr. Tingry himfelf, as be fays, tried to diffolve copal in fpirit 

 of turpentine, and the procefs did not fucceed : his notion that the 



fpirit 



