Computers are a big aid, also for the conservator. Roughly five years ago, the Van Gogh Museum entered a new and somewhat unusual research partnership with experts in the field of Electrical and Computer Engineering. Our collaborative goal was to develop new computer tools for the study of artists’ canvases. This initiative developed into the ‘Automated Thread Count Project’, co-directed by Professors Richard C. R. Johnson, Jr. and Don H. Johnson, from Cornell and Rice Universities in the USA. Application of this tool has led to fascinating new insights regarding Van Gogh’s choice of canvases in relation to other painters of his day, as this one example shows.
Counting the threads
Simply put, the computer is able to precisely count the number of threads that run near-vertically and horizontally across each square centimetre of a painting canvas. Usually the automated thread counting is performed on a digital X-ray image, which reveals the canvas weave structure of a painting.
Slight fluctuations in the spacing of the threads across a piece of canvas emerge, a natural consequence of the weaving process. These variations appear as colour-coded stripes in ‘weave maps’, forming a distinctive pattern for each canvas. When the pattern of stripes in the weave map of one painting exactly aligns with the pattern of stripes in the weave map of another painting, we can conclude a ‘weave match’ i.e. that the two canvases were cut in alignment from the same piece of woven cloth.
We were quite excited when the computer turned up a weave match between two pictures painted in Paris in 1887, one by Van Gogh and the other by Emile Bernard, his younger friend and colleague in the period.
An intimate link
It appeared that the canvases used by both painters had been cut from a single piece, not by the painters themselves, but by a commercial manufacturer. The reverse of both pictures is now covered up by an added support canvas. Yet a figure ‘6’ stamped onto the back of the original canvas used for Plaster cast of a woman’s torso shines through the backing canvas. This confirms that the canvas was commercially prepared and sold ready-stretched on a standard-sized frame, in this case corresponding to a Landscape 6 size ( 41 x 27 cm).
So it is likely that Van Gogh and Bernard visited the same artist supplies shop in Montmartre to purchase their ready-made canvases. Surely one cannot imagine a more intimate link between the practice of two painters than a shared shopping venue.