304 On Painting in Oil 
colouring was to be produced? He replied, An unity of light 
and an unity of {hadow fhould pervade the whole. He ex- 
plained to me the ditficulty of reducing the various colours 
of all the objects that may be included in a picture, and the 
various modifications of thofe colours to the fimple, harmo- 
nious ftate he defcribed, and illuftrated what he had faid by 
this fimile. «A piéture, to poffefs harmony of colouring, 
fhould look as if it was painted with one colour (fuppofe 
umber and white), and, when the chiaro-ofcuro was com- 
plete, the colour of each objeét fhould be glazed over it.” 
This obfervation, from fuch authority, was imprefled with 
peculiar force on my.mind; and if I can retrace its opera- 
tions on a fubje&t which has fo long engaged my attention, 
I fhould fay Sir Jofhua’s obfervation was the clue that guided 
me through all my experiments, and, I hope, will enable 
me to prove, that the beautiful and fimple practice which he 
fuggefted as a fimile, was literally the practice of that fchool 
upon whofe works his ideas of colouring were founded. At 
the fame time I may obferve, that the fact feems to have 
cluded his obfervation, or he would not have ufed it as a 
comparifon to fimplify his defcription of a practice which he 
thought both difficult and complex. 
In the Newtonian doétrine of light and colours, it is 
believed that all colours are inherent: in light, and are 
rendered vifible by the action of various bodies, which re- 
fle&t particular rays, and abforb the reft. Without difput- 
ing the truth of this doctrine, it is to be obferved, that a 
painter muft confider the objects he reprefents as being ana- 
logous to the materials he ufes to reprefent them; and, in 
this view of the fubject, colour is to be confidered as a pro- 
perty inherent in bodies, which is rendered vifible by the - 
contact of light, a colourlefs, or at leaft a mono-coloured 
‘fubftance, and fhadow the mere privation of light. 
A piure may reprefent either a group o figures, or other 
objects, in a room, or any objects in the open air: whatever 
the fituation may be, it reprefents certain objects in agiven 
7 . fpace, 
