Caravaggio's technique for painting – add a carafe to every canvas

The great 17th-century painter Caravaggio, whose naturalistic style shocked the art world of his time, was not above using a short cut to achieve his effects, Oxford University scientists have discovered.

One of the most-repeated set-pieces in his works is a carafe of water on a surface, which provides a startlingly realistic reproduction of the transparency, refraction and reflection of the glass and water.

Work by Professor Martin Kemp at Oxford's history of art department has shown nobody should be surprised that the carafe seems to reappear – because Caravaggio kept painting the same one, with the same light sources.

Caravaggio's technique provoked an earlier accusation from the painter David Hockney that the Old Master had used a "projection" system to cast images of a scene on to the canvas, where they could be painted directly. His method of working is now being broken down further.

The first painting in which the surprisingly realistic carafe appeared so impressed Cardinal Francesco Maria del Monte that Caravaggio was invited to join his household in Turin as a painter. Though the original "carafe painting" was lost, the theme kept turning up.

Now, after a request from the owner of The Lutenist – one of the many pictures including a reflective carafe – Professor Kemp has recreated the scene to find out where the light sources would be in real life.

One would expect the table and carafe to be below a window, but he found "the carafe was mounted more or less at a level with the centre of the window. A surprisingly high source of light – probably from an aperture cut in the ceiling or high in the wall – accounts for the flare [of light] on the right wall of [the carafe]", the profes-sor notes in the journal Nature.

But he adds: "Because the placing of the carafes in the paintings with the youths is inconsistent with this set-up, we can be sure that the carafe became a cut-and-paste motif."