2014 marks the hundredth anniversary of another important event: the first use of ultra-violet radiation for the examination of manuscripts, and particularly the deciphering of palimpsests. Scholars are frequently challenged by manuscripts which have faded to the point of illegibility, or which have been deliberately erased, or, most challenging of all, which have been erased and then written over. The Archimedes Palimpsest is one of the most famous recent examples, but palimpsests have long been exercising the minds and eyes of scholars, certainly since the middle of the 19th century.
The Archimedes Palimpsest is a medieval parchment manuscript, now consisting of 174 parchment folios
Early attempts to make unreadable manuscripts readable, dating from the 18th century, used chemicals that would react with traces of iron in the fibres of the parchment which remained after the iron gall ink used to write the text had faded or had been removed. The trouble with these techniques was that, while they might initially be successful, they ended up staining the parchment blue or brown, leaving it even less legible than it was to begin with.
Photographic techniques had also been used to enhance faded writing almost since the invention of photography in 1839. In 1894 a process was developed for revealing palimpsests which used two plates: an over-exposed plate which would show both the upper and the lower writing, and an under-exposed plate that would show only the upper writing. A positive made from the under-exposed plate could then be used as a mask to permit an image of the lower writing only to be made. While this process was successful, it was time consuming because two plates had to be made, and their registration had to be very accurate in order for the upper writing to be cancelled out as nearly as possible.
In 1914, Father Raphael Kögel OSB published a paper in the Reports of the Royal Prussian Academy of Sciences in which he explained how ultra-violet radiation from an electric arc or a mercury vapour lamp could be used to excite fluorescence in parchment, but the fluorescence would be blocked (quenched) where the ink had originally been. A photograph of the visible fluorescence could then be taken, using filters to exclude the invisible ultra-violet which would obscure the image. This paper was in distinguished company: other authors in the same volume included Einstein and Planck. UV fluorescence photography should be distinguished from UV photography: in UV photography an image is made of the invisible ultra-violet radiation reflected from the manuscript; in UV fluorescence photography an image is made of the visible light emitted by the manuscript where it has been excited by ultra-violet radiation.
Father Kögel was born Gustav Alfred Kögel in Munich in 1882; he took the religious name of Brother Raphael when he joined the Benedictine abbey at Beuron, in the south of Baden-Württemburg, in 1898. He was sent to Brazil as a missionary, but fell ill and had to return to Germany. He then entered Wessobrunn Abbey, south-west of Munich, and was ordained priest in 1906. He later studied chemistry in Vienna, and in 1912 began working with the Palimpsest Institute at Beuron, which had been set up by Father Alban Dold specifically to study the Abbey’s rich collection of Carolingian and other medieval manuscripts. Here he developed his ultra-violet imaging techniques. He had previously experimented with coloured filters and photographic plates with different spectral sensitivities to improve the visibility of the under-writing, and also with chemical methods for enhancing faded writing, even though these had been condemned at the St Gallen conference on the conservation of manuscripts more than ten years before (“… this barbaric method …”).
Kögel became a professor at the University of Karlsruhe in 1921, and set up an Institute for Technical Photochemistry and Scientific Photography. Whether because of a crisis of faith, perhaps caused by the war, or simply because he found the academic life more congenial, Kögel left the church in 1922 and married in 1924. Kögel made important advances in using UV examination in forensics, and was also a pioneer in X-ray fluorescence analysis. His greatest commercial success was the development of the Ozalid diazo photocopying process, which was widely used until the 1970s. He died in 1945.
Because of the outbreak of war, Kögel’s publication does not seem to have been noticed in English-speaking countries until the early 1920s. For example, the first edition of C. A. Mitchell’s Documents and their scientific examination (1922) does not mention the use of UV, while the second edition (1935) does. Awareness of the technique grew in the 1920s and its use was well established by the 1930s. R.B. Haselden’s Scientific aids to the study of manuscripts, published by the Bibliographical Society in 1935, gives several examples of palimpsests that had been revealed by UV photography. He warns that users should wear protective goggles and protect their skin against excessive exposure to UV, and also that “prolonged exposure to UV light is injurious to a manuscript”. Unfortunately this message was not taken on board by everybody, and I have seen manuscripts where features that were seen and photographed under UV in the 1930s are no longer visible today. Haselden advises against the use of chemical reagents to restore faded ink, but goes on to recommend the use of a solution of anthracene in alcohol (“perfectly harmless”) to enhance faded writing – the solution penetrates the paper or parchment more rapidly where there is no ink, so the writing stands out against the vivid fluorescence of the anthracene under UV. Other writers recommend the use of a mixture of Vaseline and mineral oil for the same purpose, but it hardly need be said that these techniques are not recommended.
For best results, UV examination needs to be carried out in a darkened room, using a good-quality UV lamp and while wearing UV protection glasses. It has not always been thus. My wife remembers that when she was researching in a very well-known library in the 1970s, there was only one electric socket into which a UV lamp could be plugged, and this was underneath a table. She was therefore obliged to lie underneath the table with her manuscript and the UV lamp, sometimes with a member of the library staff to invigilate.
Folio 54 verso without UV illumination
Folio 54 verso with UV illumination
The Electronic Beowulf project experimented with ultraviolet, first scanning fol. 54 verso under an ultraviolet lamp with a Kontron digital camera
UV examination is now being superseded in libraries such as the British Library which own multi-spectral imaging equipment. This gives better results as it can be much more selective than any process using filters to choose the wavelengths of fluorescence that are photographed. It uses much shorter exposures and therefore minimises the risks of exposing manuscripts to intense ultra-violet radiation. (See Christina Duffy’s blog post ‘Revealing hidden information using multispectral imaging’)
Dr Barry Knight, Head of Conservation Science & Research
Haselden, R.B., Scientific aids to the study of manuscripts, Supplement X to Transactions of the Bibliographical Society, 1935.
“Kögel, Gustav”, in Neue Deutsche Biographie 12 (1980) 295-6. www.deutsche-biographie.de/sfz43637.html
Kögel, P.R., Die Palimpsestphotographie, Sitzungsberichte der königlich Preussischen Akademie der Wissenschaften, 1914, 974-978
Mitchell, C.A., Documents and their scientific examination. London: C. Griffin & Co. (1922).