Plainsman Clays | MADI
Manganese Dioxide
Manganese dioxide colours a glaze anywhere from brown to plum and purple, and at heavy loadings the surface turns metallic. It releases oxygen twice on the way up, and the second release happens while a glaze is sealing.
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Manganese dioxide gives off oxygen twice as it heats, once between about 500°C and 600°C and again between about 900°C and 1000°C. The first release happens before most glazes begin to melt. The second happens while a stoneware glaze is softening and sealing, so a thick wash can blister where a few parts in a hundred will not. The colour runs from brown through plum to purple, and at a fifth of the recipe or more the surface turns metallic, though most metallic recipes contain other colourants as well. Getting a purple takes a high alkali, low alumina glaze fired in oxidation, and the colour is easily lost. If the kiln reduces at any point, or if the base glaze contains iron, the purple turns back to brown.
- A manganese oxide used to colour glaze, slip and clay
- Brown through plum to purple, metallic at heavy loadings
- Gives off oxygen twice as it heats, once early and once in the melting range
- A purple needs oxidation and is easily lost to reduction or to iron
