Powdering one's nose is a strategy for controlling the effects of light. The powder changes the reflectivity of the surface of the skin. Oily skin acts as a mirror which bounces light off at an angle equal to the angle at which it arrived; powdered skin is matte and reflects light in all directions. Powdering thus turns a bright, specular highlight (the kind you get on glass or polished metal, which moves across the surface of the object as you change your point of view) into a diffuse one. For an artist, getting to know the nature of highlights, grasping the fact, for example, that the end of a nose or a cheek, even a brown or black nose or cheek, will often be the brightest part of the face - brighter than the 'white' of the eye, which is, in fact, usually grey and shadowed by the eye socket - is one step on the path leading from naive to 'realistic' representations of faces.

LRB 30 November 1995 | PDF Download