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Method development and magnetic measurements properties of archaeological materials and rocks

Ntoukakis Markos

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Summary

Selection of co-belonging fragments from the numerous ceramic findings of an archaeological excavation based exclusively on the experience and patience of the conservators remains a difficult process of questionable effectiveness. While the screening of the fragments is a central prerequisite and the most important stage of the process of vase reconstruction, established methods based on scientific criteria and guaranteed efficiency for the detection of co-belonging ceramic fragments suggested in the bibliography do not exist.While the assembly of excavation fragments from their remaining thermal magnetism is suggested as a theoretically sound method in the bibliography, there are only a few older (1975) references regarding corresponding research. Research on thermoremanent magnetism in the archaeometry field since the 1980s mainly focused on the chronological dating of fired clay walls of kilns. At the same time, as reported in numerous publications, the reconstruction of vases is attempted almost solely using algorithms for optical data processing based on fragment morphology. Despite the intense scientific interest in resolving the matter using the capabilities of the new digital technology, it remains an exclusively empirical process due to the time requirements and sheer volume and complexity of the proposed methods, in order for them to be applicable in practice.The proposed methods in this paper are based on thermoremanent magnetization (A/m), which is calculated from the weak magnetic field (nΤ) measurements by a fluxgate-sensor/magnet apparatus forming a three-dimensional orthogonal system. Experimental measurements from fragments of six vases show that the magnetization magnitude of co-belonging fragments display similar values, despite the magnetic anisotropy of the ceramic material, since these belong to vases made of the same clay and fired under the same conditions. This is the criterion for finding ceramic fragments of the same vase from archaeological excavations. The thermoremanent magnetism directionality of fragments, which is aligned along the geomagnetic field at the same place and time during the vase firing process, as it is configured by their rotational symmetry, defines the position of the fragments on the body of the six vases. The shape of the original vase can be reconstructed when only a few non adjacent fragments are available. The proposed measurement apparatus can be used for the construction of a useable portable magnetometer specialized for ceramic surface measurements to achieve the above objectives. Experiments were conducted in fragments from serpentinite and were found to be oriented in a joining manner, from their thermoremanent magnetization. Investigation of the application of the method in rocks with remanent magnetization, for the localization of changes in local soil morphology, by comparing the orientation of the parent rock and its detached parts.

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