Abstract
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.
Highlights
IntroductionScientific research into ancient polychromy (painted surfaces) has expanded during the past 20 years
Scientific research into ancient polychromy has expanded during the past 20 years
The samples showing the potential presence of organic binder residues were further investigated using gas-chromatography mass spectrometry (GC–MS) targeting the analysis towards the detection and identification of the compounds belonging to the chemical families identified by Fourier transform infrared (FTIR)
Summary
Scientific research into ancient polychromy (painted surfaces) has expanded during the past 20 years. The identification of binders in samples from ancient wall paintings and polychrome art is far from straightforward: have the organic binders usually been added in a very low binder-to-pigment ratio, but these works of art are subject to degradation since they are often located in places where it is difficult to assess standard conservation conditions (open areas, uncontrolled environment, burials, settlements, etc.). Phenomena such as deamidation, hydroxylation, oxidation and carbonylation, partial hydrolysis, extensive intramolecular and intermolecular aggregation, or covalent cross-linking, cause loss of solubility in the organic binder, compromising its analysis. Such phenomena can bring about a change in the diagnostic signatures, since the residues of the original organic substances can be replaced by degradation products such as oxalates [1, 2]
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