Paper’s hidden fingerprints

The imprint of the sieve in traditionally manufactured paper may be used to verify the authenticity of a work of art.
How to establish if the print of an etching by Rembrandt dates from say 1640, during his lifetime, or from hundred years later, if, as is the case for most of his prints, the paper doesn’t carry a watermark? A new technology presented this week in a PhD thesis by Mark van Staalduinen offers an alternative identification method for handmade or ‘laid’ paper.

The technique works by analyzing the pattern of the horizontal and vertical wires that form the imprint from the sieve that the paper was made in. This pattern is so unique that it can be regarded as the paper’s fingerprint: it links the sheet to a certain manufacturer during a relatively short time period (because the sieves became progressively deformed in the paper-making process, they were not used for long periods of time).

Van Staalduinen describes the technique he developed at the faculty of Electrical Engineering, Mathematics and Computer Sciences. First, a piece of paper is scanned, either by backlighting or subjecting it to soft x-ray radiation (more expensive, higher quality). Image analysis then identifies the orthogonal lines and orientates the image with the chain lines running vertically. Van Staalduinen has shown that the combination of the distance between the chain lines (typically between 2 to 3 centimetres) and the average density of the horizontal laid lines is sufficient for making a unique identification.
There is a glitch however: the identification requires a large reference database. “The technology is very powerful”, says Dr Chris Stolwijk, of the Van Gogh Museum. “However, building up a database of tens of thousands of paper sheets costs time and money. And we don’t know yet where to get that from.” 

Mark van Staalduinen, ‘Content-based Paper Retrieval Towards Reconstruction of Art History’, 7 October 2010. PhD supervisor Professor Jan Biemond.

A TU Delft student team won a gold medal and the Best Information Processing Project Award during the international Genetically Engineered Machine (iGEM) competition at MIT in Boston. The TU Delft team developed bacteria that can pass on messages or signals to other bacteria in their environment, like a baton is passed in relay races. In this way, the bacteria can process information. This was the second time TU Delft participated in the iGEM competition. Last year TU Delft’s team won a gold medal for its ‘bio thermometer’. This year some 1,000 participants from countries ranging from Brazil and the USA to China and Australia were in Boston to compete in the 2009 iGEM Jamboree. The team from Cambridge University (UK) was the grand prize winner of the BioBrick Trophy. The Cambridge team engineered a bacterial biosensor that changes colour depending on the concentration of chemical input.

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