»a continuous […] remembrance« Axel Krefting’s reduction methods. History of its use in the Berlin Antiquities Collection, with analytical and experimental observations

Abstract

At the beginning of the 1890s, electrochemical reduction using the Axel Krefting method was introduced in Berlin's museums to remove chloride-containing corrosion layers. F. Rathgen and other heads of the chemistry laboratories recommended this simple and inexpensive method for the conservation of archaeological iron, as well as bronze, thus assuring its extensive and long-lived use. It was last used on bronzes from the Berlin Antiquities Collection in the 1970s but the method was employed since the late 19th century. An experiment was carried out where Krefting's method was recreated and used on naturally corroded coins as well as copper sheet that had been artificially corroded with chlorides. The newly formed corrosion products were then identified and compared to corrosion on bronzes in the antiquities collection. The corrosion products identified as socoformacite and spertinite could be used as an indicator of the objects being treated using the Krefting method.