Mixing manganese dioxide into slipcated porcelain

[Mashastein]

I have a test piece where I mixed manganese dioxide with porcelain powder for slipcasting, which gives a very nice light buff look. However I am concerned about manganese leaching and food safety. I used 4% manganese dioxide, is it safe for tableware? 
 

thank you all for the help in advance!

[Min]

Hi and welcome to the forum!

There are many claybodies that use manganese dioxide, granular manganese dioxide or materials like umber (which contain manganese). Main concern with using manganese oxide in claybodies, slips or glazes, are the fumes that come from the kiln firing. This is a real hazard with manganese! Make sure your kiln is either outdoors or really well vented if indoors.

Manganese oxide is not soluble in water therefore has no bio-availabilty through skin nor can it dissolve in the blood stream nor gut. Again, make sure your kiln is either outside or is really well vented if indoors. (can’t say this too many times)

Glazes should always be durable for tableware, regardless whether the claybody contains manganese oxide or not. 

What the manganese addition might do is flux the slip a bit more. I'ld also watch out for bloating if fired past cone 6, maybe only cone 5. 

 

Edited June 26, 2023 by Min
grammar

[Jeff Longtin]

Great response Min!

A local artist thought she could get away with 15% Mason Stain Black, 6600, but once she put it into production she found out, soon enough, that 15 was a nightmare.

I find 2% best. (It only creates a dark gray, however.) I'm adding it to cone 6 porcelain slip.

a note: I find a curious thing when testing colors in porcelain casting slip...the initial tests will often come out beautiful, the color looks great and the clay body performs well. It's only after the slip has sat for a week that the problems show up. For some reasons many stains, in high proportions, will cause a slip to flocculate. (Thicken up in other words.) I find iron-based stains cause a porcelain slip to gel at 5% but not so much at 4%, for instance.