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Communication Dans Un Congrès Année : 2016

Glass colourations caused by Mn-Fe redox pair

Résumé

Manganese is a chemical element used as a colourizer in glass industry since antiquity. Its capacity to be present under various oxidation states makes it responsible of a large variety of colourations. In its oxidized state (Mn3+), it imparts a strong purple to violet colour (dependant on matrix composition). Combined with iron, manganese often plays the role of a decolourizer leading to uncoloured glasses mainly used to represent hands and faces in glass windows (see for example Ferrand et al., 2015). The exact understanding of the involved reactions is however not complete and might provide information about the glass technology used in these ancient times. A series of glasses has been synthesized in order to relate the colouration of glasses with the conditions of synthesis (temperature, atmosphere, glass composition). Two temperatures have been used (1200 and 1550°C). Glasses have been synthesized under air or under reducing atmosphere (H2/N2). The glass composition has been chosen on the basis of the average of a large range of medieval glasses compositions for what concerns the main oxides (SiO2, Al2O3, K2O, Na2O, CaO, MgO). The MnO (resp. FeO) content has been varied between 1.5-x wt% (resp. x wt%), x varying from 0 to 1.5. Glass compositions have been checked by microprobe analysis at the Camparis facility of the Paris 6 university. Optical absorption spectra in the UV-Vis-NIR range have been measured at the Institute of Geochemistry, Mineralogy and Ore Formation in Kiev (UV-Vis) in the range 32000-6000 cm-1 and at the Technical University in Berlin (NIR) in the range 7000-1000 cm-1. The colour of the different glasses has been characterized within the CIE 1931 model. For a given temperature, results show that the addition of Mn in a Fe-rich glass composition implies a decreasing of the concentration in Fe2+ and an increase of the concentration in Fe3+. When the uncoloured composition is reached a further increase of the Mn content leads to glasses with a persistent pink colouration. However, results also show that uncoloured glasses are obtained for different contents of Mn according to the temperature used for the synthesis suggesting that the reaction between Mn and Fe is not a simple redox reaction. The content of Mn necessary to decolourize a glass made at 1200°C is much lower than the one at 1550°C. Finally, annealing an uncoloured glass in air leads to the reappearance of the pink colouration characteristic of the presence of Mn3+. The present set of glasses synthesized in variable conditions helps deciphering the complexity of colour making in ancient times. The effect of temperature combined with atmosphere and glass composition might provide clues to the understanding of ancient glass technology.
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Dates et versions

hal-01392924 , version 1 (05-11-2016)

Identifiants

  • HAL Id : hal-01392924 , version 1

Citer

Stéphanie Rossano, Volodymyr Khomenko, A. Bedidi, Claudine Loisel,, Jessica Ferrand, et al.. Glass colourations caused by Mn-Fe redox pair. European Mineralogical Congress, Sep 2016, Rimini, Italy. ⟨hal-01392924⟩
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