[terraforma]

First question: I'd like the simplest and most straightforward explanation of food-safe and non-food-safe glazes—an explanation that those who purchase my ceramics will understand. I want them to understand, but I don't want to scare them off if I have a piece with a non-food-safe glaze. I never use these kinds of glazes on anything intended for food, but I may make a bowl that could, for example, hold fruit. This leads to...

Question two: it seems to me that whole bananas, oranges, avocados, etc. would not pose any problems just sitting in a bowl with non-food-safe glaze.There don't seem to be leaching issues. Right or possibly wrong?

[JBaymore]

terraforma, on 15 July 2012 - 07:06 PM, said:

First question: I'd like the simplest and most straightforward explanation of food-safe and non-food-safe glazes—an explanation that those who purchase my ceramics will understand. I want them to understand, but I don't want to scare them off if I have a piece with a non-food-safe glaze. I never use these kinds of glazes on anything intended for food, but I may make a bowl that could, for example, hold fruit. This leads to...

Question two: it seems to me that whole bananas, oranges, avocados, etc. would not pose any problems just sitting in a bowl with non-food-safe glaze.There don't seem to be leaching issues. Right or possibly wrong?

When the bowl leaves your hands, you cannot control the way the consumer uses it. As a bowl that looks like a functional bowl, food function is implied to any person who might see or purchase it. Therfore, uless there is a FIRED ON label (non-removable) "not for food service use" ....... you have a potential problem there.

NO... a banana sitting is such a bowl is not an issue.... but the above factor is.

The simple answer to the first one is simply the statement "food -safe". But be sure it IS when you make such claims.

There has been a lot of discussion of this subject on these forums and a lot of info already posted. Do some searching of older threads too.

For the two actually regulated oxides in glazes in the USA (lead and cadmium), see the FDA website and the State of California websites. If you use lead or cadmium compounds there are laws that you need to comply with.

best,

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

[TJR]

Terraforma;
If you are making any type of functional pottery and selling it to the public, you should not be using non-food safe glazes as in lead glazes.John is correct as always-cadmium is not safe, nor is barium carbonate.
As a functional potter, I have had my glazes tested at a craft fair without my knowlege, and they have come out clean. I make stoneware and porcelain pots, so chances are pretty good that the glazes are safe. I avoid all lead glazes.Many commercial low-fire glazes in jars may be labelled not food safe. I would stay away from them.
There is that old story about the boy who made a mug for his dad in art class and gave it to him for Father's Day. The dad drank a cup of Coke-a Cola out of his pottery mug every night. He got sicker and sicker. Turns out the mug was glazed with lead and the dad got lead poisoning.I also avoid the purchase of mugs from Mexico, as many of the glazes involve car batteries.You can't be too careful.
TJR.The dad recovered.

[Marcia Selsor]

TJR, on 15 July 2012 - 06:36 PM, said:

Terraforma;
If you are making any type of functional pottery and selling it to the public, you should not be using non-food safe glazes as in lead glazes.John is correct as always-cadmium is not safe, nor is barium carbonate.
As a functional potter, I have had my glazes tested at a craft fair without my knowlege, and they have come out clean. I make stoneware and porcelain pots, so chances are pretty good that the glazes are safe. I avoid all lead glazes.Many commercial low-fire glazes in jars may be labelled not food safe. I would stay away from them.
There is that old story about the boy who made a mug for his dad in art class and gave it to him for Father's Day. The dad drank a cup of Coke-a Cola out of his pottery mug every night. He got sicker and sicker. Turns out the mug was glazed with lead and the dad got lead poisoning.I also avoid the purchase of mugs from Mexico, as many of the glazes involve car batteries.You can't be too careful.
TJR.The dad recovered.

So when you daughter or grand children use this fruit bowl for lemonade punch and it leaches. You won't be around to tell them oops ? you can't control what buyers will use a bowl for.DO NOT USE toxic chemicals for anything that can potentially hold food.
Marcia

[yedrow]

JBaymore, on 15 July 2012 - 06:40 PM, said:

terraforma, on 15 July 2012 - 07:06 PM, said:

First question: I'd like the simplest and most straightforward explanation of food-safe and non-food-safe glazes—an explanation that those who purchase my ceramics will understand. I want them to understand, but I don't want to scare them off if I have a piece with a non-food-safe glaze. I never use these kinds of glazes on anything intended for food, but I may make a bowl that could, for example, hold fruit. This leads to...

Question two: it seems to me that whole bananas, oranges, avocados, etc. would not pose any problems just sitting in a bowl with non-food-safe glaze.There don't seem to be leaching issues. Right or possibly wrong?

When the bowl leaves your hands, you cannot control the way the consumer uses it. As a bowl that looks like a functional bowl, food function is implied to any person who might see or purchase it.

This is an excellent point, if I may help by emphasizing it.

[Alina Albu]

I have recently read a book written by potters, for potters, about exactly the issue of safety in glazes. Very interesting, highly recommended. There are tests in there you can do in your studio in order to know if your glazes are safe (-ish). But as I am not sure I can say what the book is, as it may seem to be promoting it (which it deserves, in my opinion) , perhaps someone can suggest another way i can mention it to whoever might be interested? sorry I am new to this.

[JBaymore]

Roma, on 16 July 2012 - 09:22 AM, said:

I have recently read a book written by potters, for potters, about exactly the issue of safety in glazes. Very interesting, highly recommended. There are tests in there you can do in your studio in order to know if your glazes are safe (-ish). But as I am not sure I can say what the book is, as it may seem to be promoting it (which it deserves, in my opinion) , perhaps someone can suggest another way i can mention it to whoever might be interested? sorry I am new to this.

Roma,

Welcome to the CAD forums.

Yes you can say..... and likely it is "Mastering Cone Six Glazes" by John Hesselberth and Ron Roy. The title of that book is unfortunate... because what they have to say in a lot of it pertains to so much more than just the cone 6 range.

I do feel that I have to clarify one point you made a bit though.

There are tests you can do in your studio that give you SOME information about if your glazes are safe. They are a great start ......... and are certainly FAR better than doing nothing. But they ARE "home tests"... and far from normal engineering standard testing.....which is what industry is using and is really the "legal yardstick". Not that I am saying they are useless....... NOT by any means. I've presented on a glaze panel at NCECA with Ron and I KNOW that he knows what he is talking about. That is an EXCELLENT book.

Ther are labs that you can send tests to that give you what we might call "real numbers". It is not expensive to do. Mononna Rossol (ACTS- NY) recommends that for the non-regulated oxides you use the EPA drinking water standards as a guideline to compare to the standard leaching tests. That is a WAY conservative approach.

If you use lead and cadmium compounds and sell in the USA you MUST follow the US FDA laws and if you sell in California, also the California statutes for those compounds (Californai is tougher on this issue). There are as of yet no other oxides regulated by US law in glazes.

best,

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

[yedrow]

The "Mastering Cone 6 Glazes," is a great book. I think that I got this from that book: Most matte glazes are simply under-fired glazes. Under-fired glazes have surfaces that are like piles of rock, instead of pavement (if I may make a poor analogy). There are interstitial cavities and exposed 3d surfaces that exaggerate the effects of acids and bases on the glaze: Caustic fluids have more access to surface constituents. Ron and John also point out that not only will your food leech out, but the pot will discolor from alkalies in the dishwasher or even acid rain. That being said, I personally don't think glazes that leech a lot of anything should be sold to people. I certainly don't want an icky discolored pot with my name on it out there for 10,000 years.

[Alina Albu]

JBaymore, on 16 July 2012 - 01:45 PM, said:

Roma, on 16 July 2012 - 09:22 AM, said:

I have recently read a book written by potters, for potters, about exactly the issue of safety in glazes. Very interesting, highly recommended. There are tests in there you can do in your studio in order to know if your glazes are safe (-ish). But as I am not sure I can say what the book is, as it may seem to be promoting it (which it deserves, in my opinion) , perhaps someone can suggest another way i can mention it to whoever might be interested? sorry I am new to this.

Roma,

Welcome to the CAD forums.

Yes you can say..... and likely it is "Mastering Cone Six Glazes" by John Hesselberth and Ron Roy. The title of that book is unfortunate... because what they have to say in a lot of it pertains to so much more than just the cone 6 range.

I do feel that I have to clarify one point you made a bit though.

There are tests you can do in your studio that give you SOME information about if your glazes are safe. They are a great start ......... and are certainly FAR better than doing nothing. But they ARE "home tests"... and far from normal engineering standard testing.....which is what industry is using and is really the "legal yardstick". Not that I am saying they are useless....... NOT by any means. I've presented on a glaze panel at NCECA with Ron and I KNOW that he knows what he is talking about. That is an EXCELLENT book.

Ther are labs that you can send tests to that give you what we might call "real numbers". It is not expensive to do. Mononna Rossol (ACTS- NY) recommends that for the non-regulated oxides you use the EPA drinking water standards as a guideline to compare to the standard leaching tests. That is a WAY conservative approach.

If you use lead and cadmium compounds and sell in the USA you MUST follow the US FDA laws and if you sell in California, also the California statutes for those compounds (Californai is tougher on this issue). There are as of yet no other oxides regulated by US law in glazes.

best,

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

Hi John,

Yes that´s the book - thank you.

Very interesting reading for any potter.

Regards

[Raku]

terraforma, on 16 July 2012 - 07:06 AM, said:

First question: I'd like the simplest and most straightforward explanation of food-safe and non-food-safe glazes—an explanation that those who purchase my ceramics will understand. I want them to understand, but I don't want to scare them off if I have a piece with a non-food-safe glaze. I never use these kinds of glazes on anything intended for food, but I may make a bowl that could, for example, hold fruit. This leads to...

Question two: it seems to me that whole bananas, oranges, avocados, etc. would not pose any problems just sitting in a bowl with non-food-safe glaze.There don't seem to be leaching issues. Right or possibly wrong?

Maybe another question you should be asking is, "How do you know what the customer will use the bowl for" maybe use only food safe in all items which COULD be used for food. Maybe the Fruit bowl for examle, might be used for Salad.

[ratdog]

i too agree cone 6 is a good lesson. i dont have da money to send off a piece to test but when i get money i will .... better to have a acredited institution weigh in and for u to use the results.

cant wait to get results will help me a lot.

if u near a collage try to see if they might test it.