A STUDY OF THE DETERIORATION OF EGYPTIAN LIMESTONE SCULPTURE
S.M. Bradley, & A.P. Middleton
THIS INVESTIGATION OF EGYPTIAN sculpture has demonstrated that a number of factors, especially in combination, may be important in determining the durability of limestone objects.
- A high proportion of acid insoluble material, which is predominantly clay would appear to render the stone liable to structural decay.
- Elevated levels of soluble salts, particularly nitrates, seem to be significant, especially in respect of the susceptibility of the sculptures to localized powdering and pitting.
- Porosity, in particular the proportion of micropores, may also be significant but in this study all of the objects for which porosity data are available have a high proportion of micropores (less than 5μm) and so, on the basis of established criteria 11–13 would be expected to be of low durability.
As noted above, the sculptures from Thebes/Abydos, because of the particular properties of the limestones used are most at risk amongst those included in this study. The deterioration of sculptures of this type, which are of low durability, can be minimized by controlling environmental conditions in storage and display areas. This technique has been used successfully on another collection of sculptures in the Museum which are now stored under conditions of constant relative humidity and temperature to avoid wet-dry cycles affecting clays and to avoid hydration-dehydration cycles of soluble salts,. Conditions recommended are RH 45% ± 2% and temperature 19 ± 1°C.26
An area of study which this investigation has incidentally touched upon is the determination of provenance for Egyptian limestone sculpture. An analytical approach, using neutron activation analysis, was described by Meyers and van Zelst25 and their results permitted a distinction between limestone sculptures from around Theses and those from further north. The present study has shown that several petrographically distinct types of limestone were used for Egyptian sculpture and that these can be characterized by several analytical techniques, especially X-ray diffraction and scanning electron microscopy. Possible implications for the determination of the provenance of Egyptian limestone, using these techniques, are being actively explored.
WE ARE GRATEFUL to several of our colleagues for their constructive comments and discussion throughout this project, especially Dr. I.C. Freestone, Dr. M.N. Leese, Mr. W.A. Oddy and Dr. M.S. Tite. We are also grateful to Dr. M. Price of the Hydrogeology Research Institute, British Geological Survey, Wallingford, England for organizing the pore size distribution measurements on our behalf, and Dr. H.F. Shaw of Imperial College, University of London for assistance with the interpretation of the XRD data. We would like to thank members of the Department of Conservation, Stone Section for their help in sampling the objects and Mr. T.G.H. James, Keepter of the Department of Egyptian Antiquities and his staff for their support and cooperation throughout this project.