In painting consider the object before you, whatever it may be, as more made out by light and shadow than by lines.
A student should begin his career by a careful finishing and making out the parts; as practice will give him freedom and facility of hand: a bold and unfinished manner is commonly the habit of old age.
On painting a head—
Let those parts which turn or retire from the eye be of broken or mixed colours, as being less distinguished and nearer the borders.
Let all your shadows be of one colour: glaze them till they are so.
Use red colours in the shadows of the most delicate complexions, but with discretion.
Contrive to have a screen with red or yellow colour on it, to reflect the light on the shaded part of the sitter's face.
Avoid the chalk, the brick dust, and the charcoal, and think on a pearl and a ripe peach.
Avoid long continued lines in the eyes, and too many sharp ones.
Take care to give your figure a sweep or sway.