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Stone Spiral

Foodsafe Glaze Over Non-Foodsafe Glaze?

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I have what could be a potentially silly question. Forgive me - I'm still learning the glaze aspect of all this!

I have a glaze that I love but it is not foodsafe. I want to use it on a bowl.

 

I am wondering - can I paint with the non-foodsafe glaze, and then dip the entire piece in a clear/transparent foodsafe glaze and call it foodsafe? Does the foodsafe cover coat seal in the non-foodsafe undercoat?

Let me know what you think. I apologize again for the super-rookie question. hehe

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Unless you are willing to do a lot of lab tests, expend a lot of energy, and still find your self asking this question...the answer is still 'No'.  It simply isn't worth the risk to use a known recipe ingredient that is harmful/toxic, especially on functional ware.  As @Babs recommends...find another glaze that achieves similar results and breathe easier knowing those who enjoy your work are safe.

 

Peace,

-Paul

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No. Definitely not. The glazes will mix as they melt, essentially producing a new glaze that has all the ingredients from both glazes, including whatever is making the base glaze non food safe. Plus, when you put a clear glaze over the top of another glaze, the mixing totally changes the look of the first glaze.

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How do you know it is not food safe?

 

Roberta

I would imagine that either he is using commercial glazes that are labeled for food safe/not, or he is using recipes that are entailing the same. In both cases, trying to mix a non food safe with a food safe is really a bad idea for a functional food bearing piece of pottery. So the questions are: what characteristic is it that he likes in this particular glaze, and what makes the glaze unsafe for food. If the answer is color then he may have problems, if surface, maybe not.

 

There are glazes out there that fire to ^6-my temp, that I will not make as some of the ingredients I will not even purchase. One that comes to mind is Barium, another lead. These are too dangerous to me, as they can get absorbed in the body way too easily that they are a hazard to the potter. I even have problems to some degree with some of the other materials, and am real careful with them, Chromium, Cobalt, Manganese to mention a few. This last year, I decided not to make some mortars out of one clay using another, because the one clay used Manganese to speckle the body. I really don't know, but thought that maybe prudent to think the Manganese could get ground into the herbs and ingested. So I used a clay I knew did not have anything questionable. I usually do not worry about the Manganese speckling in functional ware, but should I?

 

 

best,

Pres 

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Pres "I usually do not worry about the Manganese speckling in functional ware, but should I?", not sure if this is a rhetorical question or not. It's the fumes coming out of the kiln from speckled clay with manganese that is the main concern.  

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I agree with Pres.  When I first started mixing my own glazes, I was very taken with a couple of recipes that used barium.  My clay supplier wouldn't even sell it to me.....he told me to do some research first.  That was good advice.  I was just wondering what Stone Spiral was basing the "not food safe" on.   On a label?  hearsay?  It is so important to do some research....and figure out your level of risk (sounds like a financial advisor, huh?) and the level of risk for whomever may be using that pot in the future! 

 

Roberta

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Pres "I usually do not worry about the Manganese speckling in functional ware, but should I?", not sure if this is a rhetorical question or not. It's the fumes coming out of the kiln from speckled clay with manganese that is the main concern.  

My concern with the Manganese in the clay body was that the grinding of the herbs in a glazed mortar pestle set could . . . possibly could. . . grind small amounts of manganese in to the herbs. So playing safe, I did not make these out of that particular clay body.

 

I am well aware of the other dangers of manganese, and try to be very careful when using it in my studio.

 

 

best,

Pres

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Guest JBaymore

Almost looks like I am being overcareful, best to err on the safe side I guess.

 

Thank you, John.

 

 

 

best,

Pres

 

There is a lot of "hysteria" out there in the ceramic community over manganese, Pres.  Yes... manganese compounds have the potential to be an issue.  But it is not 'crazy bad'.  And it is the firing issue that is the main concern. 

 

Micro-crystalline silica is the BIG one for us.  Because it is EVERYWHERE.... and pretty much impossible to get totally out of ceramics.  And the hazard is to us... not our customers.  Diffuse sources... not easy to control via local pickup ventilation.  Main control is working and cleaning practices and general dilution ventilation.

 

best,

 

.............john

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Guest JBaymore

john perfect example is warren mackenzie right? Silicosis. would also affect the glass industry too right? glass artists?

 

MacKenzie is pretty open about it.  I personally know a few potters with diagnosed silicosis.  I know one potter who died from lung cancer at a pretty young age.....but of course you can't do a direct attribution on that.  So.... maybe....??????????  I know one kiln refractories specialist that has diagnosed plural plaques associated with pre-mesothelioma .....who worked with ceramic fiber, not asbestos.  Again........ direct attribution is impossible.

 

Any occupation that gets really fine silica into the air is at risk of issues.

 

best,

 

................john

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I'll go with the "better safe than sorry" approach. Most of my pieces that could conceivably be mistaken for something to put food on or in carry disclaimers that the item is not meant for food or water, no microwaving, oven, etc., and no food safety is claimed, regardless of the commercial glaze label. I have made one exception, by category, and that is using "food-safe, non-toxic" commercial glazes for spoons and ladles and not posting a disclaimer. I am just willing to take a chance on those & testing is beyond me, Mostly, except for the spoons, it is simpler to just avoid the whole thing!  

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