A classic invention
Multispectral imaging: A scanner that sees a wider range of colours than the human eye is unlocking previously illegible manuscripts
Dec 3rd 2011 | from the print edition
TECHNOLOGICAL spin-outs from universities are usually expected to emerge from the engineering department, the school of medicine or the faculty of physics. At Oxford, however, they like to do things differently. The latest invention to emerge from the dreaming spires of England’s oldest university is the brainchild not of any of these academic Johnny-come-latelies, but rather of a group who trace their origins to Oxford’s medieval foundation: its classicists.
The multispectral-imaging scanner developed in the faculty of classics by Dirk Obbink, a lecturer in papyrology and Greek literature, and Alexander Kovalchuk, a mathematician and physicist, is able to detect traces of faded or hidden inks and paints in historical manuscripts, expose forged documents and art works, and highlight forensic evidence such as fingerprints and stains from bodily fluids. It will soon be available commercially from a firm called Oxford Multi Spectral.
Multispectral imaging works by scanning objects at a series of specific frequencies both within and beyond the visible spectrum. It is able to highlight details human eyes cannot normally see, either because they are swamped by the signal from other visible frequencies, or because they are not detectable by the rod and cone cells of the retina.
Classicists at Oxford first deployed the technique in 1999, to examine papyri discovered in a villa that was buried by the eruption of Mount Vesuvius in 79AD. They then applied it to previously illegible manuscripts called the Oxyrhynchus papyri, which were discovered in an ancient rubbish dump in Egypt. Documents deciphered using it include an epic poem from the 7th century BC by Archilochos and parts of a lost tragedy by Sophocles that dates to the 5th century BC.
Over the past decade Dr Obbink, Dr Kovalchuk and their team have both improved the hardware of multispectral analysis (which was originally developed by America’s space agency, NASA), and written more sophisticated algorithms to analyse what is seen. To start with, they had to rely on a high-resolution camera mounted on a frame, and a series of filters attached to a rotating wheel, to create a set of single-frequency images from the same perspective, in order that they could be merged as desired.
Now they have something that works like a flatbed document scanner, with a scanning head containing either six or 12 light-emitting diodes, each emitting light of a specific wavelength between 350 nanometres (ultraviolet) and 800 nanometres (infra-red). Each time the head moves across the instrument a different diode is switched on, and the results are recorded and fed into a computer.
Sometimes images taken at a specific frequency provide the best contrast. For example, iron-gall ink, commonly used on ancient documents, is transparent to infra-red light and most visible in the ultraviolet region of the spectrum. In other cases the clearest picture emerges by combining images from several frequencies. The iron-and-carbon-based ink used in one of the oldest Hebrew commentaries on the Old Testament is an example of this. Much of the book, which dates from the 10th century AD, was rendered illegible in the late 19th century by misguided academics who used shellac to varnish it. Combining data from different frequencies has highlighted the old ink and allowed the document to be read.
Besides looking at ancient scrolls, the multispectral scanner can compare things like bank notes and passports with reference documents of known provenance. Alternatively, as in the case of forensic evidence when the user does not know precisely what to expect, different combinations of frequencies can be examined to see if anything interesting emerges. As an added bonus, the new scanner also provides a novel retort to those who question the value of studying the classics in the modern world.
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