Rebecca J. Stacey

The Blackening of Paint Containing Egyptian Blue

Abstract On ancient Egyptian artifacts, paint containing Egyptian blue pigment is often found to have become brownish green or even black. Darkened paints from several coffins have been investigated using gas-chromatography/mass-spectrometry (GC/MS) and other methods, to identify the cause of the discoloration. Different phenomena have been seen: one type of discoloration involved the browning of gum arabic throughout the paint layer; other examples showed surface discoloration in the varnish, the paint underneath being still bright blue. Surface dirt also contributes to darkening. Artificial aging of paints demonstrated that gum arabic binder can discolour sufficiently for paint to appear black. The poor hiding power and transparency of Egyptian blue contribute to the overall dark appearance.

Identification, Geochemical Characterisation and Significance of Bitumen among the Grave Goods of the 7th Century Mound 1 Ship-Burial at Sutton Hoo (Suffolk, UK)

The 7th century ship-burial at Sutton Hoo is famous for the spectacular treasure discovered when it was first excavated in 1939. The finds include gold and garnet jewellery, silverware, coins and ceremonial armour of broad geographical provenance which make a vital contribution to understanding the political landscape of early medieval Northern Europe. Fragments of black organic material found scattered within the burial were originally identified as ‘Stockholm Tar’ and linked to waterproofing and maintenance of the ship. Here we present new scientific analyses undertaken to re-evaluate the nature and origin of these materials, leading to the identification of a previously unrecognised prestige material among the treasure: bitumen from the Middle East. Whether the bitumen was gifted as diplomatic gesture or acquired through trading links, its presence in the burial attests to the far-reaching network within which the elite of the region operated at this time. If the bitumen was worked into objects, either alone or in composite with other materials, then their significance within the burial would certainly have been strongly linked to their form or purpose. But the novelty of the material itself may have added to the exotic appeal. Archaeological finds of bitumen from this and earlier periods in Britain are extremely rare, despite the abundance of natural sources of bitumen within Great Britain. This find provides the first material evidence indicating that the extensively exploited Middle Eastern bitumen sources were traded northward beyond the Mediterranean to reach northern Europe and the British Isles.

Painting the Palace of Apries I: ancient binding media and coatings of the reliefs from the Palace of Apries, Lower Egypt

This study gives an account of the organic components (binders and coatings) found in the polychromy of some fragmented architectural reliefs from the Palace of Apries in Memphis, Egypt (26th Dynasty, ca. 589-568 BCE). A column capital and five relief fragments from the collections of the Ny Carlsberg Glyptotek in Copenhagen were chosen for examination, selected because of their well-preserved polychromy. Samples from the fragments were first investigated using Fourier transform infrared (FTIR) spectroscopy to screen for the presence of organic materials and to identify the chemical family to which these materials belong (proteinaceous, polysaccharides or lipid). Only the samples showing the potential presence of organic binder residues were further investigated using gas chromatography with mass spectrometry detection (GC–MS) targeting the analysis towards the detection and identification of compounds belonging to the chemical families identified by FTIR. The detection of polysaccharides in the paint layers on the capital and on two of the fragments indicates the use of plant gums as binding media. The interpretation of the sugar profiles was not straightforward so botanical classification was only possible for one fragment where the results of analysis seem to point to gum arabic. The sample from the same fragment was found to contain animal glue and a second protein material (possibly egg). While the presence of animal glue is probably ascribable to the binder used for the ground layer, the second protein indicates that either the paint layer was bound in a mixture of different binding materials or that the paint layer, bound in a plant gum, was then coated with a proteinaceous material. The surface of two of the investigated samples was partially covered by translucent waxy materials that were identified as a synthetic wax (applied during old conservation treatments) and as beeswax, respectively. It is possible that the beeswax is of ancient origin, selectively applied on yellow areas in order to create a certain glossiness or highlight specific elements.

A New Application of Fiber-Optic Reflection Spectroscopy (FORS): Characterization of Low-Temperature Alteration of Chlorite Schist and Implications for Understanding Ancient Stone Cooking Vessels

Bulk thermal alterations to chlorite schist occurring at temperatures above 450 °C are traditionally studied using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, or thermogravimetric analysis (TGA), but lower temperature changes that lead to structural and chemical alteration, including changes in oxidation state that are not followed by a crystalline modification, are not detectable using these techniques. In this paper we present the results of the first study to examine the application of fiber-optic reflection spectroscopy (FORS) for the detection and quantification of low-temperature thermal alterations in chlorite schist. Such changes have been observed during research on the thermal behavior of medieval (12th–13th centuries AD) chlorite cooking pots from the archaeological site of Merv, Turkmenistan. FORS was used to investigate these changes, testing the archaeological samples against a model data set of experimental reference specimens. The results demonstrate the potential of FORS for tracking low-temperature thermal alterations and offer the opportunity to examine temperatures attained by ancient chlorite vessels during their past use in cooking activities.