STAINING OF ARCHAEOLOGICAL GLASS FROM MANGANESE‐RICH ENVIRONMENTS*

It has been suggested that both internal and external sources of manganese may produce the black or brown staining that often occurs in buried archaeological glass. Modern potash glass of a manganese‐free medieval composition was scratched, etched and immersed in an aqueous solution containing dissolved manganese. After several weeks, immersion samples were sectioned and examined by SEM–EDX. Manganese was shown to be present in fissures and cracks within in the glass, where alkali had been depleted. Manganese from an external source is capable of blackening buried medieval potash glass.