Application of X-Ray and Neutron Tomography to Study Antique Greek Bronze Coins with a High Lead Content

Highly leaded bronze coins of the Coin Cabinet of the Kunsthistorisches Museum (KHM) show progressive corrosion as a result of unfavourable storage conditions within historic wooden cases. In connection to a research project concerning the preservation and conservation of the antique coins the causes for the sometimes severe corrosion were studied by different analytical techniques. Radiography and tomography investigations using neutrons and X-rays were performed at the Paul Scherrer Institute, i.e. the enrichment of lead in the interior of the objects was studied in a nondestructive manner. The tomography results obtained show that in addition to the lead rich areas on the obverse and reverse of the coins (often already clearly visible on the surface due to the formation of white corrosion products) a varying number of lead containing inclusions could be detected within the antique bronze coins. In addition, some information on their casting technique could be gained.