Ruzim Posted May 9, 2022 Report Share Posted May 9, 2022 I have a glaze that has about 2% manganese dioxide wich iv heard is toxic, but it also is a glossy glaze and have heard conflicting stories on if it's safe or not does anyone know if it's safe or not, thanks. Link to comment Share on other sites More sharing options...
Bill Kielb Posted May 9, 2022 Report Share Posted May 9, 2022 Technically Glazes are food safe if they contain no cadmium or lead; however what makes glazes food safe in practice? Durability, the absence of harmful oxides leaching or the glaze degrading under use. Is a glossy glaze food safe and durable because it is glossy? It can be, but unless something is tested there is no way to know with reasonable certainty. Many potters choose to just not use potentially dangerous oxides in there food wares out of an abundance of caution. If it is a commercial glaze, does it say it is food safe? Lots of commercial high manganese glazes are marked not for food use. Technically if they do not contain cadmium or lead, by definition in the states they are food safe. There is no easy answer to this question. I do not use several oxides in my food grade wares just because I am cautious. I have some high manganese recipes that resemble bronze, chrome, etc…. Very cool effect. They never go on my food wares. Link to comment Share on other sites More sharing options...
Min Posted May 9, 2022 Report Share Posted May 9, 2022 Hi Ruzim and welcome to the forum! Good place to start looking at the question of whether a glaze is suitable for surfaces that come in contact with food is by looking at the formula of the glaze. Nudge nudge wink wink….post the recipe. Link to comment Share on other sites More sharing options...
LeeU Posted May 10, 2022 Report Share Posted May 10, 2022 I largely avoid ever doing anything based on I "heard this" or "heard that". Research, research, research, from sources that have satisfied you (by doing more research!) that they are credible, valid and proven to be accurate/reliable. Link to comment Share on other sites More sharing options...
Min Posted May 10, 2022 Report Share Posted May 10, 2022 27 minutes ago, LeeU said: I largely avoid ever doing anything based on I "heard this" or "heard that". Research, research, research, from sources that have satisfied you (by doing more research!) that they are credible, valid and proven to be accurate/reliable. Absolutely! Vet your sources. Re Manganese and toxicity. Fumes from kiln firing of Manganese carbonate and dioxide are the hazard. Manganese carb and dioxide are not absorbed through the skin or by ingestion. Manganese in salt form, sulphite, nitrate or chloride are soluble and must be treated with appropriate cautions. Manganese salts are not commonly used my studio potters. This article by Dr Bill Carty addresses manganese folklore on page 9. https://static1.squarespace.com/static/527ac372e4b0d4e47bb0e554/t/560584f4e4b040325112ea61/1443202292258/GlazeSafety-Carty-2014.pdf Link to comment Share on other sites More sharing options...
Ruzim Posted May 10, 2022 Author Report Share Posted May 10, 2022 2 hours ago, Min said: Hi Ruzim and welcome to the forum! Good place to start looking at the question of whether a glaze is suitable for surfaces that come in contact with food is by looking at the formula of the glaze. Nudge nudge wink wink….post the recipe. Oh yeah and thanks for replying here's the recipe MaterialAmount Neph Sye A270 37.70 Silica 25.70 Gerstley Borate 11.90 Kaolin Eckalite 1 (IMERYS Australia) 10.50 Whiting 8.50 Strontium Carbonate 5.70 Total base recipe100.00 Rutile 4.00 Bentonite 2.00 Manganese Dioxide 2.00 Cobalt Carbonate 1.00 Total109.00 The recipe is made by Kim Ulrick Link to comment Share on other sites More sharing options...
Ruzim Posted May 10, 2022 Author Report Share Posted May 10, 2022 2 hours ago, Bill Kielb said: Technically Glazes are food safe if they contain no cadmium or lead; however what makes glazes food safe in practice? Durability, the absence of harmful oxides leaching or the glaze degrading under use. Is a glossy glaze food safe and durable because it is glossy? It can be, but unless something is tested there is no way to know with reasonable certainty. Many potters choose to just not use potentially dangerous oxides in there food wares out of an abundance of caution. If it is a commercial glaze, does it say it is food safe? Lots of commercial high manganese glazes are marked not for food use. Technically if they do not contain cadmium or lead, by definition in the states they are food safe. There is no easy answer to this question. I do not use several oxides in my food grade wares just because I am cautious. I have some high manganese recipes that resemble bronze, chrome, etc…. Very cool effect. They never go on my food wares. No it is not a commercial glaze also thank you so much for the help Link to comment Share on other sites More sharing options...
Ruzim Posted May 10, 2022 Author Report Share Posted May 10, 2022 38 minutes ago, LeeU said: I largely avoid ever doing anything based on I "heard this" or "heard that". Research, research, research, from sources that have satisfied you (by doing more research!) that they are credible, valid and proven to be accurate/reliable. Okay il keep that in mind thank you so much for the help Link to comment Share on other sites More sharing options...
Min Posted May 10, 2022 Report Share Posted May 10, 2022 Base glaze looks like it would make durable glaze when fired to maturity. Plenty of silica and alumina which is good for a durable glaze, colourants are not over the top high in that version of the glaze so that is good also. Flux ratio is good too. Manganese at that level and in that form is not a problem. Nothing I'm seeing to rule it out as a durable glaze for food surfaces. Might craze, depends on your claybody. Next thing I would do would be a vinegar and dishwasher test, instructions here if you need them. I prefer the dishwasher test to the soda ash one mentioned in that link. Link to comment Share on other sites More sharing options...
Ruzim Posted May 10, 2022 Author Report Share Posted May 10, 2022 1 hour ago, Min said: Base glaze looks like it would make durable glaze when fired to maturity. Plenty of silica and alumina which is good for a durable glaze, colourants are not over the top high in that version of the glaze so that is good also. Flux ratio is good too. Manganese at that level and in that form is not a problem. Nothing I'm seeing to rule it out as a durable glaze for food surfaces. Might craze, depends on your claybody. Next thing I would do would be a vinegar and dishwasher test, instructions here if you need them. I prefer the dishwasher test to the soda ash one mentioned in that link. Oh okay il make sure to try those tests soon thanks for all the help I'm new to the world of glaze chemistry so there's a lot I don't know yet, but it's bean a great experience so far Link to comment Share on other sites More sharing options...
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