ON THE NATURE OF DRYING OILS. 



The next intimation of folutions of amber which I have ob- Robert Boyle, 

 tained is from the works of Boyle, who gained much of his 

 information from Italian chemifts ; whence it is evident that 

 the knowledge of this preparation is of long {landing in that 

 country ; and its ufe, if it was ufed at all in the arts, is to be 

 fought for in the works of Italian artifts. 



Whoever examines the Venetian pictures with attention, On the plcWs 

 confiders that the beft artifts of that fchool were remarkable ° f ^J Venetian 

 for the facility with which they worked, and reflects on fome 

 pafTages in Lomazzo, will be difpofed to admit that the 

 peculiar fkill of the Venetian painters depended on three cir- 

 cumftances, viz. the colours they ufed, their method of ufing 

 them, and the vehicle they worked with. Of the firft, Lo- 

 mazzo gives positive information : the fecond can never be 

 known without information equally pofitive ; but of the 

 vehicle fome knowledge may be obtained by way of analyfis. 

 Till that knowledge is obtained, I may perhaps be excufed 

 for hazarding the following conjectures. 



If my experiments have not mifled me, I am entitled to Superior bril- 



draw the following conclufiohs from them. Wherever a fancy of colour 



picture is found pofleffing evidently fuperior brilliancy of 



colour independent of what is produced by the painter's ffcill 



in colouring, that brilliancy is derived from the admixture of 



foms refinous fubftance in the vehicle. If it does not yield 



on the application of fpirit of turpentine and fpirit of wine 



feparately or together, or to fuch alkalies as are known to 



diffolve oils in the fame time, it is to be prefumed that vehicle 



contains amber or copal, becaufe they are the only fubftances 



known to refift thofe menftrua. 



I have been told, and fome experiments of my own prove which appears to 



the information to be true, that the Venetian piftures, con- have be , en ambcr " 

 _ . or copal. 



iidered with refpeel: to vehicle, are of two kinds : for fome 



are extremely hard, and not at all affected by any of the above 



menftrua ; others are fimilar in colour, but fo tender that it is 



fcarcely pofiible to clean them without injury, and in that 



refpeet are little fuperior to mere turpentine colours. The 



firft, in confequence of the data which I have laid down, 



incur the fufpicion of being painted with amber or copal, but 



how are we to diftinguifli with which ? 



As each of thefe fubftances refifts equally the common Attempt to 



menftrua, perhaps the diftin&ion, can only be made by afcer- ^ e b th t e dlftinc " 



taining them. 



