A new infrared process developed by German researchers is helping scientists in Berlin work out where and when pieces of music and art were created.
They do this by searching for the so-called “watermark”, a kind of trademark printed on paper by manufacturers up until the 20th century and visible when held against the light.
The new technique involves the use of infrared light, or thermal radiation. The ink that was frequently used at the time used is transparent under this light, which means you see only the watermark without the ink or paint getting in the way.
“When I put the music sheet on the warm plate, I can see the watermark. I can then record it and send it to the computer. And from this short sequence – just a few seconds long – I look for the image where the watermark is clearest, with the most contrast, but without any ink. That’s how it works,” explains Hagen Immel, researcher at Berlin’s State Library.
Well into the 20th century, all major European paper manufacturers added this watermark to their products. Paper was an important and expensive product, and adding a watermark was a way for paper mills to stamp it – like adding a logo. The watermark images that the camera detects are stored in a database, where documents can be cross referenced.
“The watermarks are particularly important when we research handwritten papers, especially to determine the age of the document and find out where it was written. It is much easier to do this when using a watermark,” says Martina Rebmann, head of the music department at Berlin’s State Library.
Developed jointly by scientists at the Fraunhofer Institute and the University of Braunschweig, it’s hoped the technique will help find watermarks in tens of thousands of yet unidenfied artworks.
The team has already successfully dated around 60 sketches associated with Rembrandt.
But it comes at a cost – around 80,000 euros – and the next step is to develop a cheaper, more accessible version.