Some of the oldest compounds used in the colouring glass are manganese compounds. Evidence is found in early Egyptian purple glass that manganese is present.
Manganese in its low state of oxidation is colourless, but it is a powerful oxidising agent and can be used for decolourising purposes to oxidise the iron content. Glassmakers have over the years substituted manganese by sodium nitrate or selenium in decolourising. Manganese is mainly used in the production of purple glass resembling the colour of potassium permanganate (KMnO4) crystals.
The purple colour is achieved by the trivalent manganese however in its divalent state it only imparts a weak yellow or brown colour which are responsible for the green and orange fluorescence of manganese glass.
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