Colorando Auro: contribution to the understanding of a medieval recipe to colour gilded silver plates

Corrosion investigation of fire-gilded bronze involving high surface resolution spectroscopic imaging

“…Recently, a multi-analytical approach including conventional XPS and synchrotron radiation-(SR) based techniques was applied to two leaded bronzes, revealing all the interest for getting mapping of the surface chemistry of the bronze at a sub-micrometric spatial resolution [41,42]. This global approach has been recently extended to synchrotron X-ray photoelectron spectroscopy and X-ray absorption spectroscopy on mercury gilded silver plates, differently coloured according to different applied treatments based on mediaeval writings [46]. This study pointed out the interest to use SR as a highly powerful X-ray source for performing XPS surface measurements.…”

“…Subsequently, the gilded surface was burnished by an agate tool (using olive oil as a lubricant), in order to densify the porous layer and produce a smooth and shiny surface with a golden appearance. No other goldcolouring procedure, as those described in [46], was applied on the as-gilded surface. The thickness of the mercury gilding layer was estimated by SEM observation of cross sections.…”

“De Colorando Auro” medieval colour surface treatment of silver gilded statuettes decorating the Holy Lady Shrine of Huy (13th century, Belgium)

“…Indeed, iron traces can come from colouring treatments as well as from le-overs of cleaning/ polishing products such as "rouge à polir". 9 The product analysed in our test is the one used at the IRPA-KIK metal conservation studio. X-ray diffraction shows that it is composed of hydro-haematite (Fe 1.83 (OH) 0.5 O 2.5 ) which is the major constituent along with small amounts of haematite (Fe 2 O 3 ).…”

“…In the presence of a chlorinated salt spray: (i) iron K-edges are more homogeneous and seem to indicate the presence of FeCl 3 and FeOOH with variable quantities of Fe 2 O 3 , (ii) copper K-edges are homogeneous and seem to be the same as the Blank signal from the model samples although presenting different copper K-edges when freshly coloured. 10 The aim of this paper is to use the knowledge acquired from previous parts of the research, on historical sources and model samples, 1,5,6,[9][10][11][12] for the study of the historical shrine. This article brings back the research from the theoretical and model sample study to the real historical object, the Holy Lady Shrine of Huy.…”

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.…”