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Cornaline de l’Inde

Valentine Roux

I. Caractérisation et identification des techniques de fabrication des perles en roches dures

3. Identifying polishing techniques of chalcedony beads through microscopic analysis and measurement of roughness

Francesco d’Errico, Valentine Roux et Yveline Dumond

Texte intégral

1Abstract. The final stage of stone-bead manufacture implies their polishing. This corresponds to a sequence of different procedures, often called in the archaeological literature “grinding”, “polishing” and “shining”. These procedures represent the most significant and time-consuming part of the manufacturing process of stone beads. Their identification on the archaeological beads is thus necessary for the elaboration of hypotheses concerning the general organization of stone-bead production. Moreover, these “finishing” procedures result in beads of different quality, depending on the techniques employed and the time invested. Beads of different quality may characterize the producers and the owners. Their identification in archaeological materials can therefore constitute a remarkable source of information regarding the origin and circulation of different categories of beads, as well as the social groups that wore and exchanged them.

2Two types of reference-data have been used in the frame of this study to reconstruct archaeological polishing procedures: one experimental and the other ethnographic. The fieldwork in Cambay made it possible to build up a corpus of references based on a living technical tradition. Information provided by field observation and ethnographic inquiry have been complemented by historical and experimental data as well as by data from the Yemen. These two main production centers reveal two different manufacturing traditions resulting in distinct finishing techniques, different tools, energy sources and manufacturing times.

3Microscopic analysis, using SEM and optical microscopes, and measurement of roughness have been carried out on finished beads, and on beads taken from different stages of finishing procedures. These analyses enabled us to understand the transformations undergone by the bead surfaces during each stage of manufacture and to identify diagnostic attributes left by each technique on the bead surface. Archaeological beads were then studied with the same analytical tools, and by recording more traditional variables (morphological, dimensional). Intrinsic attributes analogous to those observed on modern beads were interpreted in terms of finishing techniques. When they appeared to have no ethnographic analogue, hypotheses on the manufacturing process adopted in the past were proposed based on the general mechanisms causing the formation of the various surface features observed in the reference material.

4Among the principal results obtained, it appears that, contrary to present times, Harappan bead morphology did not determine the choice of finishing techniques. Instead, there were different centers of production characterized by different technical practices, deriving from local traditions that were not necessarily diffused throughout the Indus Valley. Large classical Harappan beads appear to have been manufactured with the same technique in a single or in a few main centers. The other beads, which are characterized by a higher morphological and dimensional variability, have been produced with different techniques, probably in different minor centers of production. In the future, identification of finishing techniques on beads from different sites should enable us to identify axes of bead circulation and to assess the relationships between those sites.

© Éditions de la Maison des sciences de l’homme, 2000

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