STUDYING holograms of the furrows created when a pen is put to paper could help foil forgers.
When we write, we create characteristic microscopic indentations, especially at so-called crossover points such as the mid-point of the figure eight. To look for such features, Giuseppe Schirripa Spagnolo and colleagues from the Third University of Rome in Italy, used an instrument that precisely measures minute variations on a surface by bouncing a pair of light beams off a point and analysing the way the beams interfere. The 3D images are sensitive enough to reveal the impressions a pen creates on paper.
The team tested the technique on letters written with ballpoint pens, fountain pens and felt-tips on different kinds of paper, including thin card and tracing paper. In all cases, they were able to analyse the way the characters had been written. For example, where one pen track cuts through another, they could tell which stroke was drawn first (Journal of Optics A, vol 6, p 869).
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