Manganese dioxide (MnO2) has two primary uses in glassmaking: as a decolorizer and as a colorant. In small amounts, it counteracts the green tint caused by iron impurities, producing clear glass. When added in larger quantities, it can create a range of colors, including violet, purple, amber, and black.
Here's a more detailed explanation:
Decolorizer:
Iron impurities in raw materials can cause glass to have a greenish tint. Manganese dioxide acts as a reducing agent, reacting with the iron and oxidizing it to a less colored form, thus producing clearer glass.
Colorant:
When added in larger amounts, manganese dioxide itself acts as a colorant, producing a violet or purple hue. The exact shade depends on the concentration of MnO2 and other ingredients in the glass batch.
Historical Significance:
Manganese dioxide has been used in glassmaking for a very long time, with its use as a decolorizer dating back to ancient times.
Solarization:
Glass decolorized with manganese dioxide can undergo a process called solarization, where prolonged exposure to sunlight causes the manganese to react, turning the glass a violet or purple color.
