• Materials for Ceramics

Manganese Dioxide

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

Notes

This 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.

During firing, half of the oxygen disassociates to produce MnO (with an associated LOI of 14%). MnO is a flux. It reacts with silica to produce violet colors in the absence of alumina, browns in its presence.

Manganese dioxide is the key to Rockingham brown glazes which were 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, especially in reduction firing.

Manganese, as the material of commerce, reduces through several forms during firing (i.e. Mn2O₃, Mn3O₄, Mn2O7) on its way to being converted to MnO by 1200C.

Pure manganese dioxide is often added to clay bodies to darken their fired color, 10% is typically enough for black (or half of that for grey). For lower temperatures (e.g. 1000C) most manufacturers would not worry about metal fumes during firing. But for cone 6 and above there is disagreement as to whether they are released.

Related Information

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

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Black stain powders vs. manganese dioxide at cone 6

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The stains are still powders, showing their advantage over using raw metal oxides to color glazes. Pretty well all black glazes employ manganese along with other metal oxides, double or triple their combined percentage is needed to stain a glaze black. Much of the reason for this is that they dissolve in the melt.

An original container of manganese dioxide

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

How do metal oxides compare in their degrees of melting?

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These metal oxides have been mixed with 50% Ferro frit 3134 and fired to cone 6 oxidation. Chrome and rutile have not melted, copper and cobalt are extremely active melters, frothing and boiling. 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

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Notice how the bubbling from the off-gassing of the manganese has variegated the surface.

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

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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

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By Tony Hansen

Black ash glaze for 20% raw metal pigments: Suitable for functional ware?

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This glaze is 49% Wood Ash, 24% Soda Feldspar and 27% Ball Clay. 10 copper carbonate and 10 manganese dioxide are added to that. This beautiful sculpture was made by Dan Ingersoll, aesthetically this glaze is perfect for it. But there are two red flags here. Significant manganese and copper metal fumes are certain to be generated at cone 10 (they are seriously not healthy) so anyone using this must be very careful. But there is something much more serious - this glaze is being used on functional ware. Copper is well known to destabilize other metals in the fired glass. This 10:10 combination is a perfect storm for leaching heavy metal into food and drink. This is not an argument for the use of commercial glazes, it is one for common sense application of the concept of limit recipes.

A body containing manganese bubbles the glaze

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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).

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