Studies on the degradation of horn, antler and ivory at archaeological sites

Abstract

Horn, antler and ivory were in use extensively in the past. Prior to the synthesis of modern plastics these materials all had workable properties which made them extremely useful. The survival of these materials in the archaeological record is rare in comparison to the frequency of their use in the past, and this is made worse by the fact that they are also difficult to conserve. The literature suggests that study of these materials has been limited and that the methods of treating them after excavation are inadequate. A better understanding of the degradation of these materials within the environment and new methods of conservation treatment are needed. Furthermore, in order to identify the causes of degradation and the consequences for successful conservation, more research is needed into the nature and monitoring of the burial environment. Four different burial sites were selected for use in the study and their physical and chemical environments monitored and evaluated. Analogue samples of red deer antler, cattle horn and elephant ivory were buried at each site and retrieved after fixed time periods. Retrieved samples were analysed by weight loss, scanning electron microscopy (SEM) and microprobe analysis, Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), to establish amount of degradation which had taken place. Microbiological and biochemical evaluation suggested that collagenase production by microorganisms could play a role in the deterioration of ivory and antler within the burial environment. Analysis showed that horn samples were subject to substantial weight loss and FTIR indicated that protein breakdown had occurred. Environmental monitoring of the study sites gave a better understanding of the burial environment and the pace of deterioration. At the marine site, the slightly alkaline aerobic environment caused rapid degradation of protein by a combination of microbial attack and chemical hydrolysis, whereas the mineral component, hydroxyapatite, was protected by the seawater, leading to survival of antler and ivory but rapid degradation of horn. The brackish wetland proved to be the most protective for antler and ivory due to the waterlogged, reduced environment and presence of fine estuarine silt. Horn was usually found in extremely poor condition upon excavation, and required immediate conservation treatment since it is unsuitable for maintenance under passive conservation conditions. The estuarine environment has considerable potential for in situ preservation of organic materials, even horn, to a limited extent, and should be investigated further. Existing conservation treatments for antler and ivory are difficult, and only partially successful, so that if a suitable burial environment could be identified then preservation in situ could be an option. This study has shown that further development of new conservation treatments for these materials requires more information about the effect of the burial environment on the protein component. The development of models based on these data would also be useful in assessing how environmental change will impact on these types of artefacts at archaeological sites.

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