Nondestructive Redox Quantification Reveals Glassmaking of Rare French Gothic Stained Glasses

Abstract

The sophisticated colors of medieval glasses arise from their transition metal (TM) impurities and capture information about ancient glassmaking techniques. Beyond the glass chemical composition, the TM redox is also a key factor in the glass color, but its quantification without any sampling is a challenge. We report a combination of nondestructive and noninvasive quantitative analyses of the chemical composition by particle-induced X-ray emission–particle-induced γ-ray emission mappings and of the color and TM element speciation by optical absorption spectroscopy performed on a red-blue-purple striped glass from the stained glass windows of the Sainte-Chapelle in Paris, France, during its restoration. These particular glass pieces must have been produced as a single shot, which guarantees that the chemical variations reflect the recipe in use in a specific medieval workshop. The quantitative elemental mappings demonstrate that the colored glass parts are derived from the same base glass, to which TMs were deliberately added. Optical absorption spectra reveal the origin of the colors: blue from CoII, red from copper nanoparticles, and purple from MnIII. Furthermore, the derivation of the quantitative redox state of each TM in each color shows that the contents of Fe, Cu, and Mn were adjusted to ensure a reducing glass matrix in the red stripe or a metastable overoxidized glass in the purple stripe. We infer that the agility of the medieval glassmaker allowed him to master the redox kinetics in the glass by rapid shaping and cooling to obtain a snapshot of the thermodynamically unstable glass colors.

Looking through model medieval green glasses: From color to recipe

“…This shows that the relative quantities of Cu and Fe in the glass recipe were a critical parameter to control the final glass color from blue‐green (D2) to green (F3). Previous results on a complex medieval glass have also suggested that color control was achieved by a precise control of the added oxide quantities . The few published chemical compositions for ancient green glasses have shown that, whatever the composition type (soda, lime, potash etc), while the Fe 2 O 3 content is in the range of 0.4‐0.8 wt%, the CuO content is often larger than 2 wt%, which is much larger than the concentration used in this study.…”

“…This redox equilibrium is at the origin of the “glassmaker soap” process, which consists in the addition of manganese to glass colored by iron impurities. Iron in glass is partly present as divalent cations resulting in a greenish color . Addition of manganese results in the oxidation of iron into trivalent poorly coloring iron ions and thus removes the greenish hue of the glass.…”

“…Here, optical absorption spectroscopy (OAS) is used to probe directly the visible light spectrum and determine the nature of the coloring species. Quantitative data allow using the Beer‐Lambert's law and deriving information such as the redox speciation . Recently, strong efforts were made to develop OAS portable instruments and apply it to stained glass windows as a mobile, nondestructive, and noninvasive tool .…”

50 shades of colour: how thickness, iron redox and manganese/antimony contents influence perceived and intrinsic colour in Roman glass

“…In addition, the interpretation of the glass hue by the naked eye is subjective, so that colour description of ancient glass is highly operator dependent (Johnston-Feller 2001). In such context, it should be stressed that determination of the oxidation state of transition metal ions in ancient glass, to determine causes of colour, is a long standing question and previous studies on this topic were carried out mainly by means of X-ray absorption spectroscopy and/or other techniques, such as optical absorption spectroscopy and electron paramagnetic resonance, and were focused on a large variety of ancient glasses not only dated to Roman times but also to the Middle Ages (e.g., (Azzoni et al 2005;Quartieri et al 2005;Bingham and Jackson 2008;Meulebroeck et al 2010;Gliozzo et al 2010;De Ferri et al 2011;Arletti et al 2013;Ceglia et al 2014Ceglia et al , 2016Möncke et al 2014;Zoleo et al 2015;Hunault et al 2016Hunault et al , 2017Capobianco et al 2019). It should also be highlighted that, with optical and X-ray spectroscopies, the determination of the redox ratio of iron is easier than for other metals such as manganese (Bamford 1977;Bidegaray et al 2018).…”

Ion Microbeam Analyses of Dust Particles and Codeposits from JET with the ITER-Like Wall

“…Among the IBA methods, RBS (Rutherford Backscattering Spectroscopy) is frequently used for precise and acc , while Nuclear Reaction Analysis (NRA) and/or Particle Induced Gamma Ray Emission (PIGE) can be used to quantify concentrations of light elements, such as D, Be, C, O, Mg, and Na. Simultaneously, Particle Induced X sed to quantify Na and heavier elements [21][22][23][24][25] . Microprobe IBA methods have also been used in the past for .…”