The enigma of the silver blackening of the 13th century Notre-Dame shrine of Huy (Belgium): a surface analysis approach

The purpose of this article is to re‐examine Theophilus' and Cellini's recipes, to understand what they were used for and to find out whether they could have been used for the Notre‐Dame shrine of Huy (Rheno‐Mosan art, 13th century). A historical sample (the statuette of St Jacques the Major of the Notre‐Dame shrine) was studied with X‐ray fluorescence (XRF) in order to determine the presence of iron at its surface. The preparation of model samples gave the opportunity to study Cellini's recipe better. These model samples were characterised with colorimetric analysis, scanning electron microscopy–energy dispersive X‐ray (SEM–EDX) analysis and AES. It is observed that applying Cellini's recipe results in a colour change, due to the presence of iron and oxygen at the surface of the samples. The presence of iron at the surface of both the model samples and the statuette of St Jacques is a good indication that the recipe may have been used on the statuettes of the Notre‐Dame shrine of the Collegiate of Huy. Moreover, it is shown that the iron is not influenced by the artificial ageing of the model samples. The possible use of Cellini's recipe for changing the colour of gilding is a very new point of view to consider middle‐age shrine. The practical implications for restoration are that it is important not to change the oxidation state of the iron and so the gilding colour. It is recommended to remove the black coating on the statuette's surface but without using techniques like, e.g. EDTA baths. Copyright © 2008 John Wiley & Sons, Ltd.