We are all used to the fact that unique or very rare manuscripts, like those stored in the collections of the John Rylands Library, must be handled with extreme care. They are often only displayed to the public through a layer of protective glass or maybe even exclusively as photographic reproductions; the originals far too fragile to be brought out of the dark for extended periods of time.
Since they provide us with such a precious link to the past, it is very understandable that they should be treated in this way. So it might be easy to forget that this has not always been the case. There are many examples of manuscripts whose raw materials (usually parchment) were at one time deemed more valuable than the text they contained, and which therefore became palimpsests.
A palimpsest is a manuscript from which the text has been removed and replaced by new writing, effectively recycling the original material. This then creates a new challenge for scholars who wish to read the original text which may only be very faintly visible, if at all. Traditionally, the underlying text would have been read simply by close inspection of the faint impressions left by the writing. However, this is obviously limited to manuscripts for which this text is visible to the naked eye in the first place.
In the nineteenth and early twentieth centuries, scholars brought out the less visible text with various chemical cocktails which were often highly damaging to the manuscripts. More recently, far less invasive techniques have been developed based on a fundamental understanding of light and how it interacts with matter, and CHICC has teamed up with the Photon Science Institute (part of the School of Physics and Astronomy at the University of Manchester) to trial the technique of Multispectral Imaging.
We (George Christian and Robert Longstaff) are two fourth-year physics undergraduate students who are working with the imaging team to explore the potential usefulness of this technique. Multispectral imaging is the technique of capturing data (in this case photographs) from one source at multiple wavelengths of light. By treating these images as mathematical objects (where each pixel has a numerical value associated with it), they can be combined and manipulated in such ways as to produce images where the previously invisible text can be seen and interpreted (hopefully) much more easily. For example, often invisible text can be made very clearly visible by illuminating it with ultraviolet (UV) light. The trouble is, the text that replaced it is usually also just as visible in the image.
However, if an image taken at a wavelength where only the overlying text is visible is subtracted from the image where both texts are visible, then we are left with an image containing only the text that was previously very difficult or impossible to make out. The techniques we are using were employed on the now famous Archimedes Palimpsest, and the results they have achieved can be seen in full on their website (http://www.archimedespalimpsest.org/).
We have already had some success, although really we are learning as we go. Our main challenge is to find ways to bring out the “hidden” text as clearly as possible, and hopefully in a way that is useful to the scholars! This is a very exciting opportunity for us as it’s the first time this has been offered as a final-year project, and it offers a unique chance to work in the John Rylands Library which doesn’t happen very often for physics students!
George & Robert