ORIGIN OF COLOR IN IRON AND MANGANESE-CONTAINING GLASSES INVESTIGATEDBY SYNCHROTRON-RADIATION

The origin of colour in medieval glasses from Northern Europe has been shown to be an artifact of the oxidation states of small concentratio ns of Fe and Mn added as impurities in the alkali source. With a view to studying this phenomenon we have produced a sequence of Fe and Mn d oped glasses, produced under different degrees of oxidation, displayin g a colour range from purple through sepia, yellow, green and blue. Ut ilising the element specificity of x-ray absorption spectroscopy we ha ve been able to quantify the Fe3+/Sigma Fe and Mn3+/Sigma Mn ratios by spectral simulation of 2p absorption spectra. Fe3+/Sigma Fe changes f rom 0.53 in the sepia glass to 0.15 in the blue glass, while it appear s that the Mn3+/Sigma Mn ratio remains unaffected by the various oxida tion conditions with an approximately constant value of 0.19.