Spectroscopic Investigation of the Coloration and Fabrication Conditions of Medieval Blue Glasses

Abstract

Potash‐ and soda‐lime‐stained glasses from the 12th–13th centuries, blue‐colored by cobalt, have been investigated by Mn, Fe, and Cu K‐edge X‐ray and optical absorption spectroscopies in order to determine the oxidation state of these elements and their impact on the blue color. Remelting these historical glasses in air at 1200°C, the estimated temperature of medieval furnaces, revealed that these four glasses are more reduced before remelting. This favors Mn as weakly absorbing Mn2+, Fe as Fe2+ and Cu as colorless Cu+. Therefore Fe2+ is the second blue chromophore and copper was not intentionally used by glassmakers to obtain a blue color. A colorimetric analysis indicates that these specific melting conditions have a limited effect on the blue color of these glasses. Based on the spectroscopic determination of the redox state of Fe, Mn, and Cu, we estimate the oxygen partial pressure in medieval furnaces to be 10−7–10−9 and 10−5 bar for the potash‐ and soda‐lime samples, respectively. The comparison with previous results enables to prove the evolution of furnace technology over centuries.

Thermodynamic insight into the evolution of medieval glassworking properties

“…This study focuses on a set of seven ancient blue glass pieces, for which identification was already described elsewhere . Briefly, they were removed from French medieval stained glass windows during former restorations and were never replaced.…”

“…This study focuses on a set of seven ancient blue glass pieces, for which identification was already described elsewhere. 13 Briefly, they were removed from French medieval stained glass windows during former restorations and were never replaced. Although their exact origin is not known, they are dated from the 13th and 16th centuries by comparison with well-dated other glass pieces.…”

Nondestructive Redox Quantification Reveals Glassmaking of Rare French Gothic Stained Glasses

“…2 , 3 Only a few studies of medieval glasses have discussed quantitatively the relation among the chemical composition, the quantitative speciation of the coloring elements, and the observed color. They have allowed the rediscovery of the fabrication technique of red glasses 4 or proved the specific reducing fabrication conditions of blue glasses 5 and other glasses. 6 − 8 Quantitative chemical analyses are crucial for building historical inferences from the comparison between different samples.…”

Recycling of yttria‐stabilized zirconia waste powders in glazes suitable for ceramic tiles

“…The same evaluations can be done for Z1‐OG and Z2‐OG, respectively. The change in coloration can be explained considering the presence of chromophore elements in the sieved powders employed in Z2‐F frit, as cobalt and chromium in particular, even if present in low amount as shown in Table . Taking in account the light greenish coloration achieved we can assume also that in this case cobalt ion is fourfold coordinated .…”

“…The change in coloration can be explained considering the presence of chromophore elements in the sieved powders employed in Z2-F frit, as cobalt and chromium in particular, even if present in low amount as shown in Table 5. 24,25 Taking in account the light greenish coloration achieved we can assume also that in this case cobalt ion is fourfold coordinated. 26 Considering this result, the frit formulated with the sieved fraction of Z2AR powder must be discarded because, even if low, the amount of metallic pollutant prevents the achievement of a white glaze.…”