Speaker
Dr
Friedrich Wagner
(Physics Department, Technical University of Munich)
Description
Determination of the chlorine content of archaeological iron artefacts by prompt gamma activation analysis (PGAA)
F.E. Wagner (a), R. Gebhard (b), Zs. Révay (c), P. Albert (b), K. Kleszcz (c), H. Hess (b), P. Kudejova (b), Ch. Stieghorst (c)
(a)Physics Department E 15, Technical University of Munich, James-Franck-Straße 1, 85747 Garching, Germany; (b) Archäologische Staatssammlung München, Lerchenfeldstraße 2, 80535 München, Germany; (c) Heinz Maier-Leibnitz Centre (MLZ), Technical University of Munich, Lichtenbergstr. 1, 85747 Garching, Germany
Archaeological iron artefacts often suffer from severe corrosion after their excavation, and the presence of chlorine in the corrosion layer is known to play a major role in this process. Efforts to conserve such artefacts therefore often include treatments to remove the chlorine, for instance by leaching in alkaline solutions or by heating in inert atmospheres. To assess the necessity for and the efficiency of such treatments it is therefore important to determine the chlorine content of the finds before and after treatment in a non-destructive manner. A unique method for this is prompt gamma activation analysis (PGAA). We report on such experiments performed at the PGAA facility of FRM-2, which allows the investigation of rather large objects. A survey of about 50 objects excavated in Bavaria between the late 19th century and 2012 yielded Cl contents between several tens of ppm and 3000 ppm, but reveals no obvious correlation between the date or site of excavation and the chlorine content, which sheds doubt on the idea that the agricultural use of fertilizers during the past decades has contributed to the Cl content in archaeological artefacts. The chlorine is, however, very inhomogeneously distributed even in single objects. Experiments in which samples are leached or heated in different atmospheres showed that the efficiency of the Cl removal by leaching is incomplete even after long leaching times, while heating requires temperatures well above 600 oC.
Primary author
Dr
Friedrich Wagner
(Physics Department, Technical University of Munich)
