Janet Ambers, Scientist, British Museum
This is the latest in a series of posts about the unfolding of the Norwich shroud, a joint project between the British Museum and Norwich Castle Museum and Art Gallery
With the shroud unfolded for the first time (although still in need of much conservation attention) David Saunders, Keeper of Conservation and Scientific Research, Emma Passmore, Mellon Research Fellow, Caroline Cartwright, scientist, and I made our first visit to see what had been revealed on the inner surface.
David has a longstanding interest in the use of imaging techniques to enhance and investigate painted surfaces, and our main objective was to examine areas where text has been applied.
Using specialist cameras, we took both infrared and ultraviolet images of the shroud. Infrared reflectography is often employed in research into paintings to reveal initial sketches under the final images. For the shroud, it will make the black text clearer. This will help John Taylor with his interpretation of the hieroglyphs while the conservators continue to treat the shroud, and also allow the hieroglyphs to be published clearly for international scholars.
Imaging with ultraviolet light may help to show surface coatings and stains. Both of these approaches are very useful for objects like this as they provide information without the need for sampling, or indeed for any contact with the surface at all.
Caroline Cartwright, who specialises in fibre identification (amongst other things), took tiny samples of the linen ground (approximately two to three millimetres long) both with and without pigment.
Examining them under the scanning electron microscope (SEM) allowed her to positively identify the fibres as linen, and give the conservators information about their construction and condition.
The images here clearly show the weave of the textile, the twist direction of the fibres, and pigment sitting on the surface of the linen fibres (which appears white under the SEM). It also shows how few breaks there are in each fibre, confirming their good condition, and how surprisingly clean they are, suggesting the shroud may have been kept mostly in a folded state, and/or not extensively disturbed, be it by repeated opening and folding, handling, study or display.
My main role is to identify the pigments used. To enable me to do this Melina Plottu, our textile conservation intern from France, collected samples of the various pigments. She removed tiny pieces of single fibres with traces of colour on and placed them between two slides. I took these back to our laboratories and examined them under the microscope of a Raman spectrometer.
This equipment uses changes in the wavelength of a laser beam shone on to a material to provide an absolute identification.
Raman showed that both the light and the dark black pigments are based on carbon. There is a possibility that crushed charcoal was used for this, but the most common Egyptian black ink is known to have been produced using soot (sometimes called carbon black in the art world).
Why some areas of black text on the shroud are much lighter than others is not yet clear. The colour in the red ink comes from hematite, an iron oxide. This is responsible for the colour of red ochre, a form of red coloured earth extensively found throughout Egypt and frequently used as a pigment in Egyptian art.
Melina and Monique Pullan, the textile conservator leading the conservation, have also found a single area of white pigment, used around the area of a cartouche in the centre of the shroud. This proved to be gypsum, a white mineral common in Egypt.
The conservators were reassured to know it wasn’t huntite, another white mineral sometimes used as a pigment in Egypt – its sensitivity to moisture would have precluded many of the water based treatments used to relax and realign fragile fibres.