Different colours, or degrees of light in the background, can alone separate the object from it. They will become more detached as they differ from the colour of the object to be relieved.
The greatest relief is acquired by a ground of a neutral, or undetermined colour. But the object that is to stand out from it, depends wholly on its light and shade for relief.
According to the ground which surround colours, they will appear different to their natures. Flesh will look palest on a red ground: and a pale colour, redder on a yellow ground: and so on, always deriving their character from the surrounding one.
If any object in a composition does not sufficiently assert its place, instead of heightening the colour of it, it is generally more advisable, as the case may be, to subdue the power of its background.
The outlines of figures should be sketched with either the shadow-colour, or the colour of the ground, on which they are laid; strengthening them according to their situations.
A very useful resource, in painting, is often to look at your picture in a looking-glass, whose reflection is a copy of the picture; and the picture, being a copy from nature, a kind of analogy is established: they are both on even superfices, and both give the idea of something beyond their superfices. In viewing your picture in this manner, keep one eye shut: seeing from both eyes surround the objects too much.
Looking at your picture through the medium of a glass, blackened on one side, will, in divesting it of colour, show only its light and shade. This is a capital way of ascertaining if the latter is right.
In painting, it is a good plan to leave all you can to the imagination! it is flattering to the beholder; it gives him latitude for the exertion of his own mind; and he will supply, better than you, what you wanted, entirely to his own satisfaction—and, of course, to yours: deprive him of this, and you seldom fail to imbue him with apathy. His imagination assumes characters and forms of its own; you have set it painting: he finishes your picture, and is happy, because he has had something to do with it; and he will not quarrel with you, lest he should blame himself.
Painting should possess 'brilliancy without gaudiness, solidity without harshness, truth without familiarity, and sweetness without insipidity; all conjoined in the greatest breadth of colour.'
If a work possess the known and admitted excellencies of painting, although in the smallest and most moderate degree, it will have the peculiar appearance of looking well, which the want of them would quite invest with another character. The faults of a great mind, capable of the greatest beauties, will never appear to have a vulgar origin.