on the Nature of drying oils^ 263 s 



painting. If it is not 'fully faturated, it will abforb fome of 

 the vehicle from the colours, which is commonly termed the 

 colours finking in. 



All the colours which require grinding, (hould be previoufly Grinding co- 

 ground in fpirit of turpentine. All the pure parts (hould be lours » &c " 

 tempered with fuch a quantity of the vehicle as will enable, 

 them to lie on the pallet. The white mould be tempered as 

 ftifF as pothole. All the tints mould be made by mixing the; 

 colours fo prepared without any more of the vehicle, but they 

 mould be diluted with fpirit of turpentine, if neceflary for 

 working. 



If the ground is properly prepared, and the above caution Confequenccs o* 

 obferved in tempering the colours, it will be found that all efte ^ s ' 

 the dark colours in the piclure will bear their full tone, and 

 have a demi-tranfparency, which increafes their native bril- 

 liancy, without the dingy appearance fo common in ordinary 

 oil-painting. The admixture of white increafes the body of 

 the colours progrefiively, till there will be left in the lighted 

 parts, only fo much of the vehicle as will bind the colours, 

 and give them their full tone, but with very little of a fhining 

 appearance. When the picture is perfectly dry, it mould be 

 varniftied with a maftic or fimilar varnilh. Perhaps the bell 

 would be copal varnifh made by folution in fpirit of turpen- 

 tine, or fpirit of wine. 



The rationale of this vehicle feems to be this: the amber Obfervations, 

 and copal, when diflblved in oil, form a homogeneous mafs, 

 which dries by infpiflating, inftead of fkinning over, like the 

 common drying oils, which confift of heteregeneous parts, 

 ibme of which feparate and dry on the top. 



As the amber and copal are not foluble in any of the 

 menftruums which dillblve molt refinous fubftances, pictures 

 painted with them cannot be injured, if cleanfed with thofe 

 menftruums : and as they are extremely hard, and the moft 

 durable fubftances of their clafs, they protect the colours 

 from every kind of injury, more effectually than any other 

 known vehicle. 



No. 



