Field Conservation Methods and the Impact on Organic Residue Analysis
A main goal of field conservation is to prevent further deterioration and to promote long-term preservation of recently excavated artifacts. This is achieved by various techniques designed to clean and stabilize degraded materials. Additionally, field conservators are also able to make suggestions on proper handling and storage of artifacts, focusing on the continued preservation and longevity of artifacts. Consequently, these techniques may not preserve other important information, such as that from organic residues present on the surface or within the matrix of artifacts (Paterakis 1996). It could be considered contradictory to preserve one aspect of an artifact while destroying another. Oudemans and Erhardt (1996) argue that “there may be a difference in the purpose of conservation treatments, usually directed at preservation and consolidation of the physical, structural and optical qualities of an artifact, and treatments for organic residue analysis, primarily directed at the preservation of chemical characteristics of the original material” (104). Therefore, attention needs to be drawn to proper handling, storage, and conservation of archaeological objects, keeping in mind the preservation of all avenues of information that the object may provide.
Figure 1: Canaanite amphora sherd from Amarna with visible organic residues on the inner surface. From: http://www.amarnaproject.com/pages/recent_projects/material_culture/canaanite.shtml
Traditional field conservation techniques can interfere with organic residue sampling and subsequent analysis (Oudemans & Erhardt 1996; Paterakis 1996). Simple techniques to clean ceramics, such as mechanical cleaning with a brush or wet cleaning with water, may remove organic residues from the surface. Other techniques, such as acid cleaning and consolidation, have the potential of destroying the organic residues altogether. In addition, contaminants can skew the results of organic residue analysis or render the organic residue unobtainable. Such contamination can occur at various points in the excavation and conservation process and is usually the result of the improper handling or storage of an object. Factors, such as fingerprints, transportation, plasticizers from plastic bags, inadequate storage environments, and so on, are examples of points during the excavation process where contaminants can be introduced. Therefore, recent advances in the analysis of organic residues have created a need for a re-evaluation of the treatment and care of archaeological ceramics.
Scholars, such as Paterakis (1996) and Oudemans and Erhardt (1996), have made suggestions on proper treatment procedures of archaeological artifacts after excavation, in specific reference to the preservation of organic residues. It is stated that if organic residue analysis is to be conducted on an object, the recommendation for the handling of the vessel is minimum intervention. Such handling was demonstrated by Evershed et al. (1994) in the collection of recently excavated potsherd samples. It is stated, “Sample handling was kept to a minimum to reduce the possibility of contamination from skin lipids, and the samples were not washed or otherwise cleaned prior to storage” (910). Further analysis of these organic residues did not reveal any contaminations due to excavation or conservation.
The concept of minimal intervention will not only add to the preservation of organic residues, but also promote the preservation of the structure of the object itself. As conservators, we must be cautious of over cleaning, conserving or restoring artifacts at a risk of causing more damage than preservation. Once the information stored within an object is obtained and analyzed, other conservation techniques can be applied to the object. In this way, the full spectrum of information and preservation can be achieved.
Evershed, R. P, K. I. Arnot, J. Collister, G. Eglinton, and S. Charters. 1994. Application of Isotope Ratio Monitoring Gas Chromatography-Mass Spectrometry to the Analysis of Organic Residues of Archaeological Origin. Analyst 119:909-914.
Oudemans, Tania F.M., and David Erhardt. 1996. Organic residue analysis in ceramic studies: implications for conservation treatment and collections management. In Archaeological Conservation and Its Consequences. Preprints of the Contributions to the Copenhagen Conference, 26-30 August 1996. Ashok Roy and Perry Smith, eds. Pp. 137-142. London: International Institute for Conservation.
Paterakis, Alice Boccia. 1996. Conservation: Preservation versus analysis? In Archaeological Conservation and Its Consequences. Preprints of the Contributions to the Copenhagen Conference, 26-30 August 1996. Ashok Roy and Perry Smith, eds. Pp. 143-148. London: International Institute for Conservation.