Infrared reveals the great masterpieces' secrets (and mistakes)

Art lovers will get a chance next week to see the hidden secrets of famous paintings, revealed by infrared technology.

The National Gallery in London will unveil the early drafts and sketches under the surface paint of masterpieces by artists including Bruegel, Cranach and Raphael.

The hi-tech technique of infrared reflectography makes "under-drawings" visible by recording digital images through a television camera sensitive to infrared light. The information is processed by a computer program developed at the gallery.

The images go on display next Wednesday in the Sunley Room. Art in the Making will run until 16 February. And it will reveal that even the best artists changed their minds, or failed to get the perfect result first time.

The images show, for example, that in Jacopo Pontormo's painting, Joseph with Jacob in Egypt, dating from 1518, the artist originally placed the death-bed scene at the top left of the panel. But he later decided it would be more effective on the right, and moved it.

Other works prove that Renaissance workshops routinely produced replicas of other paintings by using tracings and stock patterns for their under-drawings. The show has been sponsored by GlaxoSmithKline which donated the scientific equipment.