Mr. Farmer says that a shining light can reveal subtle differences in the color of wood or tell you if wood furniture has been patched. Light can also show you whether the back of a painting has been relined, a restoration technique that detracts from a piece's worth. If original paint is separating from the base, well-meaning restorers sometimes apply new linen backing with resins and glues, which are heated to draw the paint back down. Good lighting is essential for an accurate assessment. Out of the darkness Some repairs are invisible to even ordinary bright light, so you'll need to take a secret-agent approach.
Black lights are ideal for ceramics and paintings.
In daylight, a ceramic crock may look like a real find. But take the piece into a darkened room and view it under the ultraviolet wavelength of black light, and repairs will appear as lighter areas. On paintings, black light exposes retouched areas. However, be wary. Masking varnishes can hide a well-executed repainting job even from a black light, which will only reveal these repairs if the varnish is removed.