Today seems to be my day for posting information that is over a year old. Thanks to the Finds and Features blog for pointing out that the following article is available online as part of Volume 1 of the Technical Research Bulletin, available on the British Museum's website (there are lots of other great articles too, about various different objects in the museum from other parts of the globe).
Writing that cannot be erased: investigations of a box of pigmented inlays from the tomb chapel of an Old Kingdom noble
Janet Ambers, Rebecca Stacey and John H. Taylor
The British Museum holds in its collections a box of pigmented inlays from the tomb of Nefermaat, a senior official of the Egyptian Old Kingdom (early Fourth Dynasty, c.2600 bc), collected by Sir Flinders Petrie in the late nineteenth century. The pieces relate to an early, and apparently rapidly abandoned, style of tomb decoration where shapes were cut into limestone slabs and the resultant hollows filled with coloured pastes. This box of inlays thus represents some of the earliest evidence for tomb decoration available for study and reflects a very different form of decoration from the tempera painting generally found in Egyptian tombs. In terms of the pigment component, the most unusual feature was the definite presence of malachite and the apparent absence of either Egyptian blue or green frit, the two frit colours which so dominate the conventional Egyptian palette. The findings for the organic fractions were even more unexpected. Analysis of solvent extracts by gas chromatography-mass spectrometry (GC-MS) showed the presence of fatty acids and diacids that are typical of degraded oils. Subsequent analysis by pyrolysis-GC-MS yielded mostly straightchain (alkane/alkene) pyrolysis products, which are consistent with a polymerized lipid; this apparently extensive polymerization implies the use of a drying oil. Linseed is the only source of drying oil known to have been available in ancient Egypt, although a number of semi-drying types, such as safflower or poppy oil, may also have been available. Th e presence of such a medium is potentially extremely significant, as the use of oil binders in dynastic Egyptian painting is virtually unknown. The use of an oil binder is unprecedented for such ancient material and may demonstrate a previously unsuspected technology.
Regular visitors will also be aware that the British Museum Studies in Ancient Egypt and Sudan is also available online.