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Hi Folks, 

I have recently painted a simple design in Magnesium oxide over a white tin glaze which matures between 1100 and 1180 C.  I read since then that Magnesium Oxide is one of the potters more toxic oxides . There is notoriously very little actual data about the safety of many glaze surfaces, but would anyone hazard an opinion as to the safety of this bowl for functional/ food use - given that the oxide is now securely bonded to a stable glaze?    I would love to use/ give this bowl away, but am worried about the toxicity of the oxide which was only put on in a wash solution.  

Any info/ opinions on Magnesium oxide gratefully received. 

Wild goose 


Polar bear bowl sept 2019  22  170512372_2.jpg

Edited by Wildgeese
corrected heading to Manganese oxide
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I think you mean manganese oxide which is very different.

It is a hazard to the Potter, not as much to the user.  The vapors released when it is fired are extremely toxic, as are the oxide itself when airborne.  Exercise caution when mixing anything containing manganese and make sure your kiln is well ventilated.

Luckily the same thing can be accomplished with a nontoxic stain or iron oxide so if you are worried, switch to something less controversial

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6 hours ago, Wildgeese said:

Any info/ opinions on Magnesium oxide gratefully received. 

This is a very good overview of both glaze safety after firing and the use of glazing materials in regards to the potters safety. It includes transition metals (aka heavy metals) including manganese. 

If in doubt then the only positive way to know if the manganese is indeed leaching from the glaze would be to have a sample lab tested which for one pot is probably not a cost effective option. If you do want to get something lab tested Brandywine Science Center was about $30 the last time I had it done. Results could then be compared the with acceptable limits found in drinking water for the specific substance tested for.


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