All Temperature Numbers Temperature Listing

932C (1709F)

Manganese compounds may begin to fume

Manganese metal fumes are toxic. It is difficult to verify the ceramic temperature where fuming could begin (welding is the context of almost all pages dealing with the topic and the level of concern regarding the dangers of manganese metal fume fever). The melting point of manganese metal is 1245C (around cone 7). However, in ceramics we use the dioxide form, MnO2. It decomposes to the monoxide form, MnO, well below typical firing temperatures. Theoretically, the MnO should be fairly stable. But in the real world material sources are crude and impure. Kiln firings are all about oxide interactions and reactions and the manganese has company - each MnO particle is surrounded, and vastly outnumbered by other compounds, especially fluxes, that may be trying to take away that atom of oxygen to reduce it to the metal form. And any production of carbon in the firing atmosphere can produce CO, hungry to do the same.

In our own testing, especially when mixed with frits, the crude granular ore of manganese melts vigorously around cone 6. And it generates gases vigorously after that.

Related Information

Decomposing manganese granular particles are causing this stoneware to bloat

This is a cone 6 stoneware with 0.3% 60/80 mesh manganese granular (Plainsman M340). Fired from cone 4 (bottom) to cone 8 (top). This body is normally stable to cone 8, but with the manganese it begins to bloat at cone 7! This is evidence that particles of manganese are generating gases as they decompose and melt at the same time as the body is vitrifying, these produce volumes and pressures sufficiently suddenly that closing channels within the maturing body are unable to vent them out.

How do metal oxides compare in their degrees of melting?

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.

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