Clay toxicity test for using in cookware

[Preeti]

What should I be concerned about w.r.t. content of the clay if I am to eat from it or cook in it. I know lead and arsenic are to be tested . I do not so much worry about the dry clay but if I were to sell cookware I do not want to sell cookware that is potentially toxic and open myself up to lawsuits from consumers. I am looking to use terracotta.

[liambesaw]

If you're concerned you can send fired samples of clay out for testing.  

One thing that limits it is a well fitting and durable glaze, which will be difficult to formulate on a terracotta since you'll need so much boron to get it to melt early.

There are clays made with spodumene that are specifically for cookware called "flameware" which are more suitable for cooking and will fully vitrify.  You will still need a special low expansion glaze, but there are recipes out there.

I wouldn't be too worried about cookware causing any sort of acute poisoning though, unless you're digging it yourself.

[Min]

@Preeti, when you say cookware do you mean ovenware like casserole dishes or pots that go on a stovetop?

As far as glaze goes if in doubt use a clear or white liner glaze for any surfaces that will come in contact with food. Are you making your own glazes or using commercial ones? Do you have a glaze that fits your terracotta without crazing? 

I've used Brandywine Science Center for having glazes tested for leaching.

 

[Preeti]

I am planning to keep my pots unglazed since I want my pots to have pores and the glaze would seal that . Please do let me know if there are places that will test the fired pots for me .

Min , I meant pots that go on stovetop.

[Min]

Unglazed flameware made from terracotta? What would seal the clay from oils etc soaking into the clay and going rancid?

[Bill Kielb]

6 hours ago, Preeti said:

I am planning to keep my pots unglazed since I want my pots to have pores and the glaze would seal that . Please do let me know if there are places that will test the fired pots for me .

Min , I meant pots that go on stovetop.

Pots that go on stove tops would be generally considered flame ware. They generally require a clay that resists the extreme temperature differential without cracking.  There is a real concern someone could burn themself severely if things go wrong  suddenly. 

Food safe in the states is designated as no lead or cadmium however most potters realize that chromium, lithium, vanadium, barium, and other colorants and fluxes  all have risk to human health as well if they leach and are consumed. Testing is expensive and often hard to define as to all things to test for, and under what conditions.

I think you have several issue here. I suggest you read a bunch about flame ware to understand which products potters try and use for direct flame application then whatever you can about leaching  levels of toxic or semi toxic chems. It’s quite difficult to test all forms of potential leaching and whether the component can leach enough to exceed limits established For human consumption.  Many  potters stay away from using anything with potential for this reason.

Terra cotta is yet another category that is generally porous yet many feel seasoning of the surface adds to the taste of their food. The more research the better to understand the potential for bacterial growth etcetera. 

Finally to make matters just a bit more complicated durability, What is it to you ? Is it direct flame or is it erosion of the clay and glaze in a dishwasher or is it the ability not to leach when exposed to acid and base foods or maybe all of the above or even still, if I bump the pot into something, will it crack.

Lots of reading I know, but most experienced potters have defined these things for themselves then make pots as they believe are safe, or durable, or not for food, etc.....

[Preeti]

Min

Yes the clay will go rancid after a while so they are not meant for keeps (couple uses ) Hence I am not worried about durability etc . I am worried about aesthetics and chemicals that leach at high temperatures/normal temperatures. Do not want to be charged for lead laced food (or any other toxins ) or eat lead laced food myself :- ) Thanks a lot for indulging :-)  I have not been able to find a place that will test this for me.

 

[Min]

@GreyBird had a clay analysis done, you could pm her and ask where she had it done and the cost. I really don't think leaching from the clay will be an issue though. What I would be concerned with would be liability issues, flameware isn't made by many people, it's one of the harder things to get right. 

[neilestrick]

Most moist clay bodies have a 'Certified Non-Toxic' label. This label is required by the government, and falls under ASTM D4236, Standard Practice for Labeling Art Materials for Chronic Health Hazards:

 1.1 This practice describes a procedure for developing precautionary labels for art materials and provides hazard and precautionary statements based upon knowledge that exists in the scientific and medical communities. This practice concerns those chronic health hazards known to be associated with a product or product component(s), when the component(s) is present in a physical form, volume, or concentration that in the opinion of a toxicologist (see 2.1.11) has the potential to produce a chronic adverse health effect(s)..

Art materials can be certified non-toxic, or have other health safety warnings according to what's in them, for instance 'Only for use by people over the age of 13'. The certification only applies to the material in the state in which is is sold, e.g. moist clay. It does not apply to the clay once it has dried  or has been fired. That said, they test for lead and other heavy metals during the certification process, and have to be found in levels low enough that they don't pose a chronic health risk in order to be listed as non-toxic. Once fired, I can't image those materials would pose a greater risk than when the clay was moist.

There is a tradition of using non-glazed, porous terra cotta for cooking. Personally, it grosses me out so I don't do it. Maybe for baking bread I would, but certainly not for roasting a chicken as some do. I think that selling something like that is opening you up to all sorts of liability issues. Flameware also opens you up to a lot of liability, too. I know of a couple of studios who sell flameware pots, but it's a level of risk that I'm not comfortable with myself. You'll need to do a lot of testing if you plan to sell it to the public. All it takes is one pot cracking in half on the stove top and spilling hot stuff onto someone to ruin their life and yours. Also, flameware is not porous. It is vitrified, high fired stoneware, so that may not work for you.

If you end up selling pots for use on the stove top, I highly recommend that you do not describe them as being for use on the stovetop. They will not work on an electric stove of any sort, only on gas stoves (flame).

[neilestrick]

I would also think about the environmental impact of making pots that are only meant for a couple of uses.

[Preeti]

@neilstrick I would think the environmental impact is actually on the positive + for something I am trying to do , but thanks for bringing it out. I understand and appreciate your elaborate comment on flameware. 

I am wondering if the "non-toxic" label also means its food safe ...@Min mentioned @GreyBird would know where to get clay tested for lead, cadmium and barium. I suspect there should be a list of things it needs to be tested for to be "food safe"  Here  is something I would like to be able to say for my pots : https://miriamsearthencookware.com/about-miriams-earthen-cookware/know-your-food-know-your-cookware/

 

[liambesaw]

7 minutes ago, Preeti said:

@neilstrick I would think the environmental impact is actually on the positive + for something I am trying to do , but thanks for bringing it out. I understand and appreciate your elaborate comment on flameware. 

I am wondering if the "non-toxic" label also means its food safe ...@Min mentioned @GreyBird would know where to get clay tested for lead, cadmium and barium. I suspect there should be a list of things it needs to be tested for to be "food safe"  Here  is something I would like to be able to say for my pots : https://miriamsearthencookware.com/about-miriams-earthen-cookware/know-your-food-know-your-cookware/

 

I'd take the statements made on that website with a GIANT grain of sand.  They claim their cookware is biodegradable and compostable, of which clay is neither.  By definition clay cannot biodegrade because it is non organic.

They also claim that from the digging of the clay to the firing of it everything is 100% GREEN with ZERO negative impact on the environment, but that's absurd.

Anyway, that entire website reads like a pseudoscience mumbo-jumbo scam, I'd refrain from that kind of rhetoric.

[neilestrick]

12 minutes ago, Preeti said:

@neilstrick I would think the environmental impact is actually on the positive + for something I am trying to do , but thanks for bringing it out. I understand and appreciate your elaborate comment on flameware. 

I am wondering if the "non-toxic" label also means its food safe ...@Min mentioned @GreyBird would know where to get clay tested for lead, cadmium and barium. I suspect there should be a list of things it needs to be tested for to be "food safe"  Here  is something I would like to be able to say for my pots : https://miriamsearthencookware.com/about-miriams-earthen-cookware/know-your-food-know-your-cookware/

 

From a technical/legal standpoint, the non-toxic label does not mean it is food safe. A glaze can be certified non-toxic but not be food safe, and vice versa. In the US, all restaurant dishes are required to be made of vitrified clay with a smooth surface that can't harbor bacteria.

I totally agree with @liambesaw. Most of what is being promoted on that website is marketing mumbo jumbo. Any commercially available clay bodies will likely have the same test results. She claims her clay is so pure that it's edible, and so is any commercial clay body with a non-toxic label. Nutrients? She also implies that pots that the rest of us use a lot of chemicals in making our pots, which is ridiculous. Even clays from 'isolated' areas can have naturally occurring lead in them. Where does she think lead comes from? It's an element, after all. I have a hard time believing that there is zero ppm lead in her clay. I'd like to see the actual report with the name of the lab, etc. The biggest danger with her unglazed pottery is the risk of food-borne illness from not using it properly since it's porous.

[Preeti]

Thanks interesting take and its a good thing I asked :-) since I am a newbie !!  However I was just focused on her test and results the pdf that says the clay has no lead , arsenic or cadmium .. I do not intend to source my own clay so I either buy from a source that can say that or do my own test and be able to say that.

 

[liambesaw]

4 minutes ago, Preeti said:

Thanks interesting take and its a good thing I asked :-) since I am a newbie !!  However I was just focused on her test and results the pdf that says the clay has no lead , arsenic or cadmium .. I do not intend to source my own clay so I either buy from a source that can say that or do my own test and be able to say that.

 

Like min said above, she uses http://www.bsclab.com/Pottery_Testing.html to test her glazes, they have a phone number on that webpage and you can call and ask if they'll test your fired samples of clay (I'm sure they will)

[Mark C.]

What I have to stop eating my clay-rats I have been toasting it in my waffle maker for late breakfasts . The only down side I thought was having to drink so much water to wash the porcelain clay down as it gets a bit sticky in the throat.

You have to appreciate a good mumbo-jumbo story

[Bill Kielb]

5 hours ago, Preeti said:

Thanks interesting take and its a good thing I asked :-) since I am a newbie !!  However I was just focused on her test and results the pdf that says the clay has no lead , arsenic or cadmium .. I do not intend to source my own clay so I either buy from a source that can say that or do my own test and be able to say that.

 

Just a word of caution, everyone above has been cautious for good science and experience reasons. It’s interesting to look at the clay analysis posted on the website  and note that there are no lab references,  testing protocol references, number of samples, control, chain of custody references .......... I could go on and on. That aside though the test they are citing is one for nutrient analysis of soils for plant growth. Typically these samples are taken at root depth along fairly regular intervals in soil to determine viability of plant growth. Very organic stuff, but not clay.

Its also interesting that the whole ten acre area sampled at a 20 foot depth is the representation. One sample for ten acres?  Looking at the analysis I do not see any clay as in forms  of Kaolin? Iron seems to be missing as well. What gives, is this clay at all?

Analysis for arsenic and lead, both natural, really end up to look quite different than merely stating this test did not discover any. This test is not Intended to test for many of these substances so it would appear that more research and confirmation of these claims is prudent.

Lead, arsenic, cadmium, mercury, barium, uranium, all very natural substances btw and iron is everywhere! Except in this 10 acre swatch I Guess. A final thought, lead is the progeny or decay of Uranium generally. Before it was lead it was probably more dangerous in some ways.

I would research this a bit more before believing it. Just an opinion though.

[Min]

On the one hand it is amusing to read the  mumbo jumbo on that site but on the other had it irritates the heck out of me. She is doing a disservice to all of us who are diligent about making wares responsibly. For those of us that sell our work I'm sure you are like me in that there are always customers asking about lead or cadmium etc. We try and educate them about what we do and the materials we use, making durable glazes etc. Then along comes someone who fear mongers by saying things like this:

"Ceramics are made up of many chemicals, metals, and minerals. They are obtained by fracking and other environmentally destructive means of mining. These chemicals include but are not limited to barium, cadmium, chrome, cobalt, lead, lithium, nickel, selenium and vanadium, silicon dioxide, feldspar, silicon carbide, magnesium oxide, petalite (an ore of lithium).  And all of these raw materials range in toxicity from mild to highly toxic. It is a mixture of individually mined and extracted chemicals and oxides. So it has to be fired to very high temperatures to fuse. In order for food to not come in contact with these chemicals, so-called ‘food safe’ glazes and enamels are used. These glazes or enamels are a paint-like substance with their own set of chemicals/toxins. They include lead and cadmium which can leach into food every time."

 

[Bill Kielb]

4 minutes ago, Min said:

On the one hand it is amusing to read the  mumbo jumbo on that site but on the other had it irritates the heck out of me. She is doing a disservice to all of us who are diligent about making wares responsibly. For those of us that sell our work I'm sure you are like me in that there are always customers asking about lead or cadmium etc. We try and educate them about what we do and the materials we use, making durable glazes etc. Then along comes someone who fear mongers by saying things like this:

"Ceramics are made up of many chemicals, metals, and minerals. They are obtained by fracking and other environmentally destructive means of mining. These chemicals include but are not limited to barium, cadmium, chrome, cobalt, lead, lithium, nickel, selenium and vanadium, silicon dioxide, feldspar, silicon carbide, magnesium oxide, petalite (an ore of lithium).  And all of these raw materials range in toxicity from mild to highly toxic. It is a mixture of individually mined and extracted chemicals and oxides. So it has to be fired to very high temperatures to fuse. In order for food to not come in contact with these chemicals, so-called ‘food safe’ glazes and enamels are used. These glazes or enamels are a paint-like substance with their own set of chemicals/toxins. They include lead and cadmium which can leach into food every time."

 

I agree, my opinion is snake oil without regard to who it affects. Just my opinion though. Real potters generally work hard and struggle to understand as much as they can to make their wares reasonably safe. This stuff does not appear to help much.

[neilestrick]

14 minutes ago, Min said:

"Ceramics are made up of many chemicals, metals, and minerals. They are obtained by fracking and other environmentally destructive means of mining. These chemicals include but are not limited to barium, cadmium, chrome, cobalt, lead, lithium, nickel, selenium and vanadium, silicon dioxide, feldspar, silicon carbide, magnesium oxide, petalite (an ore of lithium).  And all of these raw materials range in toxicity from mild to highly toxic. It is a mixture of individually mined and extracted chemicals and oxides. So it has to be fired to very high temperatures to fuse. In order for food to not come in contact with these chemicals, so-called ‘food safe’ glazes and enamels are used. These glazes or enamels are a paint-like substance with their own set of chemicals/toxins. They include lead and cadmium which can leach into food every time."

 

I can't tell if she's incredibly ignorant or intentionally fear-mongering in order to sell her work.

Is she really claiming that there's no silica in her clay?

[liambesaw]

15 minutes ago, neilestrick said:

I can't tell if she's incredibly ignorant or intentionally fear-mongering in order to sell her work.

Is she really claiming that there's no silica in her clay?

It borders on parody, but I think it's a mixture of both.

Someone should tell her that surface clay from Boston is probably not quite as clean as mined kaolin

[Callie Beller Diesel]

That website looks like a false advertising lawsuit waiting to happen. She’s insinuating a lot of medical claims about her cookware being more beneficial than other stuff, but providing no backup. Her claims are all kinds of problematic, and I’m using that word because the  forum software edits out the one I think really applies. 

[liambesaw]

4 minutes ago, Callie Beller Diesel said:

That website looks like a false advertising lawsuit waiting to happen. She’s insinuating a lot of medical claims about her cookware being more beneficial than other stuff, but providing no backup. Her claims are all kinds of problematic, and I’m using that word because the  forum software edits out the one I think really applies. 

I went with mumbo jumbo 

[Callie Beller Diesel]

There are concerns we as potters have to mind, but the ones this woman is talking about can best be described as distorted.

@Preeti You’ve mentioned that you’re a beginner and that you’ve got concerns about toxicity in your ware. I think I’m safe in saying that we as a group would like to help you make the best ware you can, with the most accurate information possible. Can you help us do that by sharing a little bit about your level of experience, and what exactly you’d like to make? If we know wether you want to make some pots for you and your family or if you’re planning on going into business we can hopefully give you the best information for your situation without overwhelming you. 

[Preeti]

@Callie Beller Diesel thanks for your kind words. I have some experience making small/mid size pottery (cups bowls/pots etc ) and I am not looking to make anything that requires more  than 5lbs of clay (at least for now) :-) . I am looking to use them for cooking/storing warm food. The clay I'd like to use is terracotta. I am looking to go into business  hence am concerned about liability issues in particular  esp since things need to be "food grade"

I do not wish to glaze my pots.