How to spot a perfect fake

The works were full of striking, scrupulous detail. On Jerome’s arm, for example, dozens of faint horizontal cracks have appeared; every so often, a clean, vertical split intersects them. In French canvases from the 18th century, cracks in paint tend to develop like spider webs; in Flemish panels, like tree bark. In Italian paintings of the Renaissance, the patterns resemble rows of untidy brickwork. On the Saint Jerome, the cracks match perfectly. 

Fascinating article here.