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

Abstract

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.

Ancient ‘gilded’ art objects from European cultural heritage: a review on different scales of characterization

“…Studies in the field of archaeology, technical art history and conservation, report analytical data about the identification of provenance/origin, composition and manufacturing techniques of gold objects (coins, sculptures, paintings) and its alloys used for decorating surfaces 2, 4, 12, 18, 20–99…”

“…If gold fingerprinting can be carried out by elemental analysis and in few cases by isotopic one (achievable only for lead and osmium32), the decoration, joining, mounting and surface finishing techniques can be characterized through accurate observation under different lights and radiations in order to obtain information on the surface morphology that can also reveal invisible details 25–26, 46–50, 87, 92, 94, 98–99. The careful observation of the surface pattern and behavior of materials (presence and type of cracks/craquelure, varnishes or other finishing layers, traces of sharp tools, etc.)…”

“…Although many research studies were dedicated to archaeological metal artifacts coated with gilding layers,5–10, 13–16, 20–21, 27–30, 32–35, 86–89 some interest was showed to other typologies of gilded art objects, mainly wooden sculptures, retables and altarpieces, leather and parchment‐based objects (such as illuminated manuscripts or gilt leather decorations on wall) and wall paintings from the European cultural heritage 12, 19, 26, 31, 36–85, 91–99…”

“…A wide range of imaging and spectroscopy‐based techniques is nowadays available for analysis of gilded art objects (Table 2): from optical microscopy (OM, PLM), infrared reflectography, thermography, to scanning/transmission/environmental electron microscopy (SEM/TEM/E‐SEM), confocal microscopy coupled with laser profilometry, atomic force microscopy (AFM), FTIR and Raman microscopy (micro‐FTIR, micro‐Raman), X‐ray spectrometry (WDXRF/EDXRF/TXRF, XPS), ion beam analyses (PIXE/PIGE, RBS, SR), etc 1–2, 5, 12, 18, 20–34, 38, 41–42, 49–99…”

Colorando Auro: third century colouring surface treatment of fire gildings

“…a-Fe 2 O 3 was detected in the coloured area. 5,6 In that recipe, reagents containing iron are apparently very important to bring about changes in colour. In the recipe presented here, no iron is present in the reagents used.…”