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Manganese Dioxide

Alternate Names: Mno2, Pyrolusite, Manganese(IV) oxide

Notes

Above 1080C, half of the oxygen disassociates to produce MnO, a flux that immediately reacts with silica to produce violet colors in the absence of alumina, browns in its presence. Thus if it is being used in glazes fired below 1080C it should be considered as MnO₂, if above it should be taken as 81.5 MnO and 18.5 LOI.

In glazes it will behave in a refractory manner, stiffening the melt. Because to the expulsion of oxygen at 1080, glazes using manganese should avoid this temperature range to reduce the chance of blistering and ruining of the glaze surface.

This material is available as a pure material or as a ground ore (pyrolusite). Thus while generically it is pure MnO₂ the actual name-brand materials may only be 75% MnO₂.

Manganese dioxide is the key to Rockingham brown wares which are made by employing about 3% iron oxide and 7% manganese in a transparent lead glaze of a recipe such as: Feldspar 28, Kaolin 14, Flint 4, Lead bisilicate 40, Whiting 4.

Manganese browns have a different, often more pleasant character than iron browns.

Manganese oxides can occur in a number of less common forms: (i.e. Mn2O₃, Mn3O₄, Mn2O₇).

Related Information

Manganese dioxide powder (left) and manganese carbonate (right)

An original container of manganese dioxide

This bag will give you a clue as to what manganese dioxide, MnO₂, is mainly used for. Staining bricks.

A body containing manganese bubbles the glaze

Laguna Barnard Slip substitute fired at cone 03 with a Ferro Frit 3195 clear glaze. The very high bubble content is likely because they are adding manganese dioxide to match the MnO in the chemistry of Barnard (it gases alot during firing).

How do metal oxides compare in their degrees of melting?

Metallic oxides with 50% Ferro frit 3134 in crucibles at cone 6ox. Chrome and rutile have not melted, copper and cobalt are extremely active melters. Cobalt and copper have crystallized during cooling, manganese has formed an iridescent glass.

An example of variegation on a tile surface that occurred when using raw manganese dioxide (likely due to gassing)

How do you turn a base cone 10R dolomite matte into this beautiful tan?

You add up to 5% manganese dioxide. The base recipe is G2571A. The clay body is a buff burning stoneware having iron speckle. The quality of the surface is excellent and it is durable.

Cone 10R dolomite matte glaze with 5% manganese dioxide

By Tony Hansen

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By Tony Hansen