mrcasey Posted December 16, 2021 Report Share Posted December 16, 2021 A couple of local chemists volunteered to test our oatmeal glaze. I did some quick and dirty estimates: Suppose it takes 100 grams of glaze to cover a mug (probably less). About 70 grams is dry weight and half of that is on the outside. 3% of 35 grams is 1.05 grams of manganese. The top test tile lost about 5% of its manganese over a month of continuous submersion in the vinegar. Rounding up, the inside of the mug would lose about .06 grams of manganese in a month. An unidentified source on the internet suggested that people not ingest more than .01 grams of manganese per day. Some vitamins contain .004 g. I'm assuming that the leaching is linear and it doesn't all come out at once. I'm also assuming that as the glass wears down, the leaching won't increase. If all this is kosher, I feel like the oatmeal has an acceptable level of manganese leaching. Does this seem reasonable? Link to comment Share on other sites More sharing options...
neilestrick Posted December 16, 2021 Report Share Posted December 16, 2021 10 minutes ago, mrcasey said: The top test tile lost about 5% of its manganese over a month of continuous submersion in the vinegar. This is far, far more abusive than any real world situation. In the real world I think the worst it would get is someone might leave some coffee in a mug on their office desk over the weekend. So by your numbers I would expect that the level of leaching in a real world situation would be negligible. With manganese we are generally more concerned about the safety of the potter, who has to deal with the risk of inhaling the dry manganese, as well as the fumes from the kiln. Link to comment Share on other sites More sharing options...
Min Posted December 16, 2021 Report Share Posted December 16, 2021 I'm seeing silica, alumina, colouring / texturizing oxides but no fluxes to speak of in that analysis. Link to comment Share on other sites More sharing options...
Bill Kielb Posted December 16, 2021 Report Share Posted December 16, 2021 4 hours ago, mrcasey said: If all this is kosher, I feel like the oatmeal has an acceptable level of manganese leaching. Does this seem reasonable It’s an interesting analysis and may seem extreme because it’s magically vinegar but in the real world as that cup gets placed in the dishwasher the glaze erodes probably the most. So over time as the durability decreases, does the leaching stay the same? I would be careful in assuming we are being conservative and have addressed the maximum credible with this single test with a single solvent from a single sample firing etc….. Link to comment Share on other sites More sharing options...
mrcasey Posted December 16, 2021 Author Report Share Posted December 16, 2021 3 hours ago, Min said: I'm seeing silica, alumina, colouring / texturizing oxides but no fluxes to speak of in that analysis. They only tested for those metals and my only real concern is manganese. Link to comment Share on other sites More sharing options...
Min Posted December 16, 2021 Report Share Posted December 16, 2021 1 hour ago, mrcasey said: They only tested for those metals and my only real concern is manganese. Have a read through of "An Overview of Glaze and Glazing Safety" by William M. Carty and Hyojin Lee Kazuo Inamori from the School of Engineering at Alfred University, link to it here. In particular from page 9 regarding manganese: "Inhalation of these vapors creates a readily available reactive species for adverse interactions with the body (and internally through the lungs and mucus membranes). Even small amounts can be readily absorbed into the bloodstream. The oxides of manganese, MnO and MnO2, are both insoluble in water and do not pose a threat. The Mn is not soluble and therefore not available, cannot be absorbed through the skin or even an open cut, and even if ingested, cannot dissolve into the blood stream. Mn obtained from a salt (chloride, nitrate, or sulfate) is soluble, so if the source of Mn is a salt, exercise appropriate care." Reason I queried which fluxes were used was to get a fuller picture of the glaze. If there are sufficient levels of alumina and silica in the molecular unity formula then chances of glaze degradation (in a fully melted glaze) are reduced. We don't have that info with an incomplete formula. Reduce the likelihood of leaching then you have a more durable glaze, Mn or no Mn. Link to comment Share on other sites More sharing options...
mrcasey Posted December 17, 2021 Author Report Share Posted December 17, 2021 The glaze is Oatmeal from Mastering Cone 6 Glazes. The dudes who wrote that book were real sticklers for safe glazes Frit 3195 20 % Wollastonite 29 % Nepheline Syenite 4 % EPK 32 % Silica 17 % : 102% Manganese 4% Rutile 6 % Link to comment Share on other sites More sharing options...
Min Posted December 17, 2021 Report Share Posted December 17, 2021 Enjoy making, glazing and using your pots, no worries about that glaze. Link to comment Share on other sites More sharing options...
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