[ H9 ] 



— it fliould be thus prepared before the grind- 

 ing. 



There are two ufeful colours I have not men- 

 tioned, white and black, which fome count no 

 no colours at all. I think they may be termed 

 the two extremes of colouring, fmce the one is 

 the ftrongeft light we can lay on, and the other 

 the deepeft fhade. Thefe are feldom ufed pure, 

 but are mixed with other colours. The white 

 (where colours are laid on in a body) mixed, in 

 different propo^rtions, with any other colour, 

 makes all the yariety of fli^de§ that the two 

 colours fo mixed are capable of producing. 

 White may be cprnppunded with any fimple or 

 compound polour, to produce different fliades 

 thereof. Black is often mixed (a little of it) in 

 the fliades, wherp the objedt is of a beautiful and 

 and primary cploijr, as red, blue, or yellow ; for 

 thefe colours, ihadowed with fine dark colours 

 pf their own fpecies, would be too glaring, and 

 quite unnatural -, fo that it is neceffary to allay 

 them with black, or fome dull colour 5 for if 

 you obferve nature itfelf, for example, a fine 

 red or blue garment, it will appear exceeding 



