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13-04-2015, 10:14

Laboratory Methods

Once in the laboratory, prehistoric plant fiber artifacts and impressions may require further processing before the initiation of analysis. Generally, this involves cleaning and/or stabilization as well as providing adequate storage conditions.

Cleaning and Stabilizing

The procedures described below do not constitute a complete collection of cleansing and preservation techniques, nor are they surefire ‘recipes’ that can be mechanically followed with instant and satisfactory results. The laboratory treatment of specimens or impressions is never uniform and requires a certain amount of adaptation and adjustment of methods. The procedures should be based on a thorough knowledge of the constitution of the specimen prior to treatment and an understanding of how it got to be that way.

Some general admonitions can be stated, though these certainly are not rules. The analyst should treat each fiber specimen or impression as if its condition were unique despite the fact that its state of corrosion or deterioration may roughly be ascribed to a particular type (e. g., waterlogged, carbonized). The specific reaction of different specimens to the same treatment may be distinct.

Common sense is a major ingredient in the treatment of specimens or impressions. There is nothing wrong with altering procedures in midstream. Caution is the watchword and the specific procedures described are simply indications of the range of treatments that might be employed. Before detailing specific cleaning and stabilizing techniques, the following points are offered as guidelines.

As little as possible should be done. If a fiber artifact is still flexible and stable, ‘no’ agents should be applied unless it is clear that further deterioration is likely to occur. This also applies to impressions whose matrix is adequately consolidated.

The long-term effects of additives must be considered. This is one of the major problems in the stabilization of plant fiber constructions. Certain agents, such as shellac and its allies, must be avoided. Once employed as a virtual panacea, this preservative is now known to transform into a black, brittle, insoluble mass that obscures the specimen and cannot be removed without causing damage. Oil-based pesticides or fungicides break down with time and release harmful residues that ultimately destroy the specimen. As noted by Adovasio, many additives render material unsuitable for radiocarbon assay, and this fact must be seriously considered in the laboratory as well as on the site.

All commercial preparations are to be chosen with extreme care, as their composition is subject to change with little or no advance notice. Alterations in proportions or strengths and substitutions in ingredients may produce entirely different results than previous versions of the compound. A preparation that does not list all the ingredients and their relative proportions should never be used until it has been tested on expendable samples. Similarly, no preparation that differs even slightly from an earlier formula in concentration of ingredients should be employed without prior testing.

While it is widely agreed that any conservation method employed to stabilize fiber artifacts should be reversible, there are sometimes conditions which mandate the use of nonreversible techniques. An excellent case in point is the remarkable collection of burial fabrics and assorted wooden artifacts recovered from the Windover Bog in Florida. Due to the advanced decomposition of the interior of many of these superficially stable items and the unsuitability of any other preservation techniques, all but a small ‘control’ sample of the Windover fabrics and wood were conserved via parylene conformal coating, a non-reversible technique which is described and discussed in Adovasio et al.

Without proper environmental control after treatment, all preservative techniques may be of little use. For fiber specimens, this means maintenance of stable temperature and relative humidity (RH). Ideally, temperature should not exceed 70 °F (or mold growth may begin) and RH should not be less than 62% (or the object will be desiccated). Fluctuating temperature and humidity are the most destructive agents. Protection from excessive light is also necessary. Ordinary incandescent lights can cause fading; most fluorescent lights are potentially worse, and prolonged exposure to direct sunlight is the most damaging of all. Specimens should be stored in polyethylene bags sealed with masking tape, or, preferably, one of the commercial transparent tapes. When humidity or temperature cannot be controlled, the careful sealing of bags is imperative.

Space precludes any further discussion of specific cleaning and stabilizing procedures to be employed with dry or wet site perishables.

Final Preparation

After the cleaning and stabilizing procedures have been completed, the specimens and impressions are nearly ready for analysis. Actual examples of prehistoric fiber artifacts generally require no further processing, but impressions and positive casts taken from impressions may need an additional preparatory step. Frequently, the detail on impressions or positive casts is difficult to perceive even under the best lighting conditions. In order to maximize the data potentially available from such specimens, it is often advantageous to coat the surface with talc applied via a soft brush or with sublimated ammonium chloride. These procedures bring the technical details into sharp relief and greatly facilitate their analysis as well as photography. The results are often spectacular and well worth the minimal effort involved.

Logistic preparation for the analysis of actual fiber artifacts and impressions are minimal. A clean, well-lighted area with plenty of layout space is desirable, along with a variety of instruments. While unaided visual inspection is occasionally sufficient, the analyst must often resort to a 5-10 x hand lens or a variable-power stereoscopic microscope; hence, these instruments should always be available. An ideal analytical milieu includes a variable power stereoscope with an integral high-resolution digital camera connected to a HD large format screen with image capture capabilities.

Considerable prodding and poking is frequently necessary to expose details of manufacture and a variety of metal probes should be on hand for this purpose. Measurements should be taken in the metric system with a precision sliding or digital caliper.

Proper lighting is crucial to the analysis of fiber artifacts and the analyst should experiment with a variety of combinations to achieve the best results.