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Rembrandt under X-ray at the British Museum

Medical technology is being utilised to obtain clear images of watermarks

A new piece of equipment at the British Museum is proving an invaluable support for traditional methods of print connoisseurship.

Traditionally, the identification of watermarks has relied on published collections of traced outlines such as the invaluable volumes of Briquet, published in 1907. While remarkable studies in themselves, the drawings can only be a fairly imprecise guide to the often faint lines and confusing forms.

The use of X-ray machines to record watermarks has been in use since the 1960s. In the field of Rembrandt studies—where it has been widely used since then—it was first applied as a means to draw conclusions about dating and print editions in 1961 by Christopher White and K. Boon in their catalogue of the artist’s prints. In the 1980s X-rays were taken of watermarks of 600 prints by Rembrandt in the National Gallery of Art Washington. These were used for comparative purposes by the Rijksmuseum who X-rayed around 400 of their Rembrandts in 1988 and collated the results of their study. The Amsterdam findings will be incorporated into a major study of Rembrandt’s prints, to be published at a future date.

The method developed in the 1960s relied on beta-radiography using a carbon 14 radioisotope and was a lengthy process. Two further methods are widely used at the British Museum. According to Janet Lang, responsible for overseeing tests on works on paper, the choice of which method is used depends partly on the nature of the paper. Most prints and drawings are, she says, radiographed using electron radiography using a 320 KV Seifert Isobolt X-ray set to fairly standard settings.

Recently, however, a method derived from medical X-rays has been developed and this has proved to be particularly useful for the study of print watermarks. This relies on “soft” X-radiography using a low power X-ray beam. Its use for prints and drawings was pioneered by H.M.M. van Hugten and print dealer and collector Theo Laurentius in Holland. As well as watermarks, it can record the image of the so-called chain and laid lines which are part of the manufacturing process of the paper and can also reveal much about a print or drawing’s history.

At the British Museum a JME microfocus X-ray set is operated at about 8 kV with a low current and exposures of a few minutes. With the microfocus unit the image is very sharp although the contrast is not as marked as with a beta radiograph.

Soft X-radiography has not been in widespread use as the type of equipment is not widely available. The British Museum’s machine, which costs around £12,000 and has been funded by print collector Samuel Josefowitz, is Russian made and is supplied by a company called JME who mainly produce large industrial radiography equipment. According to Ms Lang, it produces fast results, enabling larger batches of material to be X-rayed. Images can be scanned and read on computer, allowing for image enhancement. From the computer they could be transferred to CD-ROM, a possibility which could have great potential for the dissemination of information.

There are still some technical problems: none of the methods outlined above are satisfactory for prints which are laid down on to backing sheets. Sadly, most of the British Museum’s Rembrandts are currently laid down and the Department of Prints and Drawings needs funding to embark on a project to lift them off.

It is important to stress that useful results from making X-rays of watermarks rely on comparison: simply looking at one or two in isolation is no more helpful that applying standard methods of connoisseurship. The various projects currently underway or recently completed, including a study of the prints of Bellange at the British Museum, of Jan Muller at the Rijksmuseum and Schongauer by a private dealer, have used information about watermarks to draw conclusions on issues such as which papers artists were using at various points in their careers; whether they used random sheets or worked their way through batches of paper in a systematic way (as Rembrandt seems to have done); and whether particular designs of watermarks were reused by paper mills several years apart. From this sort of information it is possible to draw firmer conclusions on issues such as when particular states of prints were printed and how posthumous editions by later publishers were produced.

Whether the new technology has implications for the market remains to be seen, but it is not impossible to imagine sale room catalogues in years ahead carrying photographs of X-rays of watermarks.

Originally appeared in The Art Newspaper as 'Rembrandt under X-ray'