A young lad dressed in a cap and pointed slippers sits hunched over a sheet of paper at work on a drawing. Beside him a dog is curled ... in linseed oil yielded an especially saturated black; a lump ...

Red chalk is warmer than black: see the emotional intensity of Polidoro di Caravaggio’s (no, not that one) head of St Thomas. And when colour is actually deployed in the drawing itself, as in the ...