What raking light actually shows you

Under the flat frontal light a gallery uses, a painting reads as a picture. Drop the lamp until it is almost parallel with the surface and it stops being a picture and becomes an object: every ridge of paint throws a shadow, and things that were invisible a moment ago — the weave of the canvas, the ridge where an old tear was filled, the ghost of a stretcher bar, a signature added later over dry paint — all stand out.

It is the cheapest diagnostic in the business and still one of the most revealing. It will not tell you what pigment was used or what is under the surface; for that you need infrared and x-ray. But it will tell you very quickly whether the object in front of you has the surface it ought to have for its age and its supposed author.

Every painting we offer is examined this way before it is catalogued, and the photography goes to any registered bidder who asks.