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Tyler Miller

Raw clay and heavy metal leaching

Callie Beller Diesel

To clarify for future readers, this thread has been split from a post in the name of allowing technical conversations to continue that have gone well beyond the scope of the original post. For reference, you can find the original post here.

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There are two issues at work here.  One ceramic, one legal.  The legal aspect, is jurisdictionally related and is best left to the OP to figure out in their jurisdiction.  Legal advice from legal experts, ceramics advice from ceramists.  Mmkay?  Good.

The second question is re: non toxic cookware body.  Terracotta, as has been mentioned, has been considered the standard cookware the world over for millenia across all human cultures.  Firing low (like cone 017), sealing with oil, and using a heat diffuser on the stovetop are all you need.  There are other flameware bodies (which are better suited to certain applications), but if it’s for personal use, not commercial, or if it’s for a market that you’ve done your due diligence on, terracotta is the best option.  Flameware clay bodies require a lot of R and D to make work, especially of glazed.

Edited by Tyler Miller

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10 hours ago, Tyler Miller said:

There are two issues at work here.  One ceramic, one legal.  The legal aspect, is jurisdictionally related and is best left to the OP to figure out in their jurisdiction.  Legal advice from legal experts, ceramics advice from ceramists.  Mmkay?  Good.

The second question is re: non toxic cookware body.  Terracotta, as has been mentioned, has been considered the standard cookware the world over for millenia across all human cultures.  Firing low (like cone 017), sealing with oil, and using a heat diffuser on the stovetop are all you need.  There are other flameware bodies (which are better suited to certain applications), but if it’s for personal use, not commercial, or if it’s for a market that you’ve done your due diligence on, terracotta is the best option.  Flameware clay bodies require a lot of R and D to make work, especially of glazed.

Sounds as if you are pro terra cotta actually, which is fine. I think many of the responses have been to highlight the latent issues around certain thinking as  ....... it’s hard to predict what the future intentions of the end user will be.  Having said that, have you visited and read the website representation that appears to have started this for the OP?

“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/

Just curious of your thought after reading through a bit?

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1 hour ago, Bill Kielb said:

Sounds as if you are pro terra cotta actually, which is fine. I think many of the responses have been to highlight the latent issues around certain thinking as  ....... it’s hard to predict what the future intentions of the end user will be.  Having said that, have you visited and read the website representation that appears to have started this for the OP?

“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/

Just curious of your thought after reading through a bit?

The website is health washing. 

Re:  lead cadmium and barium (and arsenic! mentioned on the website).  As long as your clay isn't coming from an industrial waste dump, it's a non issue?  Cadmium that doesn't come from ceramics really only comes from industrial waste (google "itai-itai disease").  I'm pretty sure arsenic salts as a general rule sublimate out before earthenware matures (google that, though).  I'm also pretty sure that any chemically significant amount of lead in a clay body (significant enough to cause toxicity issues) would have undesirable effects as a body flux on the clay in question.  

But that's giving too much credit to the issue.  Before you have a solution you have to have a problem.  I have never once heard of someone being poisoned by means of a terracotta vessel.  Risks of lead glazing, cadmium pigments, chrome pigments, copper, cobalt, silica, barium etc etc all of these are characterized well enough in the literature to establish some kind of risk assessment.  But where are the clay poisoning cases?  People eat clay (Geophagia - sometimes in areas of poverty and famine by pregnant women to obtain vital minerals in the absence of other sources), people rub it all over their bodies, use it to stop bleeding (google Coolclot).  Like, I'm sure someone's made a pot with mine tailings and that didn't work out for the end user, but it's literally not an issue.  Just maybe no anti-scumming barium?

Edited by Tyler Miller
typo

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1 hour ago, Tyler Miller said:

The website is health washing. 

Re:  lead cadmium and barium (and arsenic! mentioned on the website).  As long as your clay isn't coming from an industrial waste dump, it's a non issue?  Cadmium that doesn't come from ceramics really only comes from industrial waste (google "itai-itai disease").  I'm pretty sure arsenic salts as a general rule sublimate out before earthenware matures (google that, though).  I'm also pretty sure that any chemically significant amount of lead in a clay body (significant enough to cause toxicity issues) would have undesirable effects as a body flux on the clay in question.  

But that's giving too much credit to the issue.  Before you have a solution you have to have a problem.  I have never once heard of someone being poisoned by means of a terracotta vessel.  Risks of lead glazing, cadmium pigments, chrome pigments, copper, cobalt, silica, barium etc etc all of these are characterized well enough in the literature to establish some kind of risk assessment.  But where are the clay poisoning cases?  People eat clay (Geophagia - sometimes in areas of poverty and famine by pregnant women to obtain vital minerals in the absence of other sources), people rub it all over their bodies, use it to stop bleeding (google Coolclot).  Like, I'm sure someone's made a pot with mine tailings and that didn't work out for the end user, but it's literally not an issue.  Just maybe no anti-scumming barium?

Interesting, I am actually surprised at the analysis on the website as the test published is questionable and I am a little more apprehensive with respect to lead and arsenic after reviewing hundreds of  EPA soils reports.  Terra-cotta is popular with many though. As to eating raw clay I would be reluctant to advise it especially for those I have reviewed reports on.  ( Lead is cumulative) As far as poisoning cases  there are many due to natural substances actually And the ingestion of them. I think everyone was trying to be cautious and point out the more you know, the better your choices.  Maybe just  like the nutrient test represented as taken over ten acres, the more one researches from a variety of sources with reasonable discrimination probably the better.

Just a quick add, decided to As you suggest google a little research on background levels of chems and it is pretty consistent with tests I have seen....... and present just about everywhere. See below:

EC674180-6B3A-48B9-BD4D-3D2E38C1C657.jpeg

Edited by Bill Kielb

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A lot of problems with cadmium in Asian rice farms, as far as I know theyre not growing their rice in industrial runoff.  It's a problem because rice is a bioaccumator of it.  Anyway, terra cotta has been used for thousands of years, that doesn't make it ideal, or practical, or special, or even especially useful.  Cooking and serving yourself is fine, but since this is a business question, you have to expect answers about liability and such.

I have heard that restaurant flatware needs to be vitrified, but i've never come across any sort of regulation like that while researching FDA tableware rules.  Their only concern seems to be acceptable limits of lead, cadmium and phthalates and the 20mm lip and rim rule.

I mean go ahead and do whatever you like, we are just trying to highlight points where there may be danger and liability issues from a business standpoint, since you are looking to cook and serve on these pieces as a business. 

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8 hours ago, Bill Kielb said:

Interesting, I am actually surprised at the analysis on the website as the test published is questionable and I am a little more apprehensive with respect to lead and arsenic after reviewing hundreds of  EPA soils reports.  Terra-cotta is popular with many though. As to eating raw clay I would be reluctant to advise it especially for those I have reviewed reports on.  ( Lead is cumulative) As far as poisoning cases  there are many due to natural substances actually And the ingestion of them. I think everyone was trying to be cautious and point out the more you know, the better your choices.  Maybe just  like the nutrient test represented as taken over ten acres, the more one researches from a variety of sources with reasonable discrimination probably the better.

Just a quick add, decided to As you suggest google a little research on background levels of chems and it is pretty consistent with tests I have seen....... and present just about everywhere. See below:

EC674180-6B3A-48B9-BD4D-3D2E38C1C657.jpeg

Bill,

 I took the time to find the context of the article you posted there.  I'm not sure it's saying what you're thinking it does?  Full article you excerpted is here:  https://maxwellsci.com/print/rjees/v3-541-545.pdf 

Health Canada's maximum acceptable concentration for arsenic in drinking water is "10 ppm" this can be expressed as 10 μg/g (see link here https://www.healthlinkbc.ca/healthlinkbc-files/arsenic-drinking-water).  10 micrograms per gram is the maximum concentration allowed to be contained in drinking water.   The article expresses that the average As content of the earth's crust is 2 mg/kg of soil (2 ppm), with a range of 1-50 mg/kg possible (pages 541-542 of the article).  In the context of this article's discussion on clay soils containing arsenic and mercury.  4/11 samples were within acceptable limits for drinking water, 3/11 are more or less at the MAC, and those that weren't are within 8.47 μg/g (ppm) of being so.  And that's unfired soil samples and a limit set for drinking water--likely a very conservative limit for soil for clay.  There is no mention of a firing schedule, temperatures reached, etc.  This article, to mind, establishes that arsenic poisoning from clay from the developing world isn't an issue if the clay isn't contaminated.  The devil's in the details, in this case, knowing that 10 ppm of As is an acceptable standard of drinking water and that μg/g of something is equal to its ppm.  I would not put too much weight in the authors' knowledge of ceramics however, because they advise "the earthenware products should be well fired to reduce Hg levels to the lowest minimum since Hg has a tendency to evaporate at high temperatures."  Arsenic also does this, as previously mentioned, and the mercury level is remarkably low (I'm sure your broad experience will agree).  This might suggest that the implications of this data may not be entirely clear to the authors. 

If, as you say, As is at these levels pretty much everywhere.  We're golden.  No issues.  Arsenic is within acceptable levels in some cases to drink the soil.  Not saying anyone should drink soil, but what Health Canada says and the Ghanan scientific community have to say is interesting.  I would like to see the many cases of heavy metal poisoning from eating clay.  Soil ingestion is usually cited as a potential cause of lead poisoning, but it's also not something I've heard of happening in real life (maybe it was a thing when gas and paint were still leaded?).  I feel like poisoning via soil poisoning is more likely to come from bacteria or parasites than the discussed metals and arsenic.

Cadmium in rice:  

I don't know a lot about this, but the sense I get is that it's a concern in the sense that Cd is indeed an issue with rice, there have been historic incidents of contaminated grain, but actually characterizing the risk has been difficult.  It seems like more of an economic issue (rejecting grain that exceeds maximum allowable levels). Articles that gave me this sense:

Canadian discussion of Cd in rice.  In over 55% of samples Cd was undetectable.

https://www.inspection.gc.ca/food-safety-for-industry/chemical-residues-microbiology/chemical-residues/cadmium/eng/1369229974936/1369230037986

2008 Hong Kong discussion on this issue

https://www.cfs.gov.hk/english/multimedia/multimedia_pub/multimedia_pub_fsf_26_01.html

2017 Article discussing cadmium uptake.

https://www.sciencedirect.com/science/article/pii/S0269749116321376

Interestingly,  Arsenic might be more of an issue with rice than Cd:

https://www.fda.gov/files/food/published/Arsenic-in-Rice-and-Rice-Products-Risk-Assessment-Report-PDF.pdf

As for terracotta being practical, useful, special or ideal, as a student of world cuisine I'd strongly disagree.  Things heat and caramelize differently in earthenware.  A well-seasoned tajine or cazuela is magical, a seasoning unto itself.  Clay pot rice (I think called smashed flying rice) from Vietnam is one of the best things ever.  Beans taste better when cooked in unglazed clay and La Grande Confrérie du Cassoulet have strong opinions on what kind of vessel their prized dish is baked in (glazed earthenware .  This is a point of taste, no one ever need cook on terracotta and life is complete without it, but to me, it's definitely special, like cast iron or tinned copper ware.

All the best guys.

Edit: In the interest of balanced discussion, I've found this article on Fish consumption advisories I'd bookmarked (in particular, Ontario's, which I use)  which includes much more stringent consumption guidelines (and a critique of their adequacy).  I suspect the reason for these guidelines being more stringent is that the chemicals found in fish are much more bioavailable than in drinking water.  An example of how this is significant is the potential for a dammed waterway to release inorganic mercury from the soil into bioavailable things like methyl mercury by means of bacteria action.    Google Site C Dam in BC for a current case study of this effect.

Article:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5381969/

Relevant Table:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5381969/table/t1/?report=objectonly

And a much loved resource (don't eat salmon from Erie or Ontario):

https://www.ontario.ca/environment-and-energy/eating-ontario-fish

 

 

 

Edited by Tyler Miller
Clarified potentially weaselly words and added a balancing article, plus typo

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2 hours ago, Tyler Miller said:

Bill,

As for terracotta being practical, useful, special or ideal, as a student of world cuisine I'd strongly disagree.  Things heat and caramelize differently in earthenware.  A well-seasoned tajine or cazuela is magical, a seasoning unto itself.  Clay pot rice (I think called smashed flying rice) from Vietnam is one of the best things ever.  Beans taste better when cooked in unglazed clay and La Grande Confrérie du Cassoulet have strong opinions on what kind of vessel their prized dish is baked in (glazed earthenware .  This is a point of taste, no one ever need cook on terracotta and life is complete without it, but to me, it's definitely special, like cast iron or tinned copper ware.

All the best guys.

 

 

 

 

I’m good with all the human consumption allowances, and they often change as time provides more data.. The point is, lead and arsenic and mercury are  virtually everywhere (background levels)  and in  most clay. Assuming I fired it all out may be a good assumption or a bad one. Being concerned with lead is real. Eating raw  clay is probably not generally good advice in most situations. The earth is made of this stuff, it’s everywhere in many varying levels. Clay might stop bleeding and then again may cause other issues. Folks have used terra-cotta for many generations and some feel it flavors their food. That’s, fine. The virtue of it being terra-cotta does not make it immune from issues, including bacterial growth nor as @liambesaw mentioned the best product for a use,

I understand you favor terra-cotta, but others don’t for their reasons. One thing for sure, what we know with virtual certainty is that It’s highly unlikely to have zero contaminants or “bad things” in any particular clay and the test posted is likely questionable.

Over representing good qualities anecdotally while dismissing any potential bad qualities is generally not realistic. All the comments have been cautious and intended to be helpful including those of potential legal representation, or food for thought if you will.

My conclusion was, most experienced potters do what they do after reasonably  and discriminatory informing themselves and producing what they are comfortable with. Taking the broad position that something is just fine for anecdotal reasons seems to not fully inform. Your argument seems to be Terra-cotta is just fine because it always has been. That’s fine, folks do what they do for reasons they are comfortable with. In a situation where a person is concerned with contamination I am uncomfortable representing there is none and if there is ........ it’s all good stuff, or it likely is all burned away at lowfire temps but strangely not at much higher temps, I guess.

Edited by Bill Kielb

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27 minutes ago, Bill Kielb said:

My conclusion was, most experienced potters do what they do after reasonably  and discriminatory informing themselves and producing what they are comfortable with. Taking the broad position that something is just fine for anecdotal reasons seems to not fully inform. Your argument seems to be Terra-cotta is just fine because it always has been. That’s fine, folks do what they do for reasons they are comfortable with. In a situation where a person is concerned with contamination I am uncomfortable representing there is none and if there is ........ it’s all good stuff, or it likely is all burned away at lowfire temps but strangely not at much higher temps, I guess.

I seem to have stepped into something unintentional.  I said two things in my initial comment.  1) There is a legal aspect of this that should be discussed with the proper experts 2) There is a ceramic aspect, which, given the conditions of the OP, is terracotta.  I also said flameware bodies are superior in certain applications.  The reasoning for my comment was the cost of research and development of a flameware body for personal use is disproportionate to its benefit.  I would argue that the proper development of a flameware body for market is cost prohibitive for reasons related to the legal aspects (in Canada, I wouldn't try it).

I then came to the defence of terracotta as a non-toxic material.  The cited website's claims and studies are absurd, but so is the worry of toxicity of fired terracotta.  My reason for saying this is that it's not a known issue.  Firstly, if there were lead or cadmium in a meaningful form in a commercial terracotta body we'd know about it, especially the Californians.  MSDS would contain it.  So it's not a mainstream issue.  Secondly, if you were to dig for the clay, you're doing a lot of testing,if bringing that to market, and the clay content is going to come to light anyway.  Thirdly, there's no history of terracotta causing poisoning (FDA calls this generally recognized as safe).

I'll fully concede the drawbacks.  It is porous, until properly sealed.  But so is cast iron, which will rust and leach and cause all kinds of issues if not properly cared for.  It will break, and probably when fully of liquid and hot.  I would never sell a terracotta body on any scale, and that's where a proper flameware body comes in.  I'm of the opinion that studio potters shouldn't mess with flameware commercially because it's too much work and too much trouble to come back at you when things go bad. 

I apologize.  I've misrepresented myself.  I think we're in more agreement than initially thought, the devil is just in the details.

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9 hours ago, liambesaw said:

I have heard that restaurant flatware needs to be vitrified, but i've never come across any sort of regulation like that while researching FDA tableware rules.  Their only concern seems to be acceptable limits of lead, cadmium and phthalates and the 20mm lip and rim rule.

This came from a conversation I had via email with someone from the FDA back in 2017. I also found it written in the FDA rulebook at the time or he sent me some literature, but I can't find it now. But if you read all of their other rules regarding sanitation, everything must be sealed, even the walls in the kitchen. They specifically mention that cast iron shouldn't be used because it is slightly surface porous and difficult to clean, unless it is being used for cooking at high enough temps to kill bacteria. You couldn't use it as a plate. All of those rules would lead one to believe that unglazed terra cotta would not be allowed as a food contact material unless it was sealed with an FDA approved material.

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38 minutes ago, neilestrick said:

This came from a conversation I had via email with someone from the FDA back in 2017. I also found it written in the FDA rulebook at the time or he sent me some literature, but I can't find it now. But if you read all of their other rules regarding sanitation, everything must be sealed, even the walls in the kitchen. They specifically mention that cast iron shouldn't be used because it is slightly surface porous and difficult to clean, unless it is being used for cooking at high enough temps to kill bacteria. You couldn't use it as a plate. All of those rules would lead one to believe that unglazed terra cotta would not be allowed as a food contact material unless it was sealed with an FDA approved material.

Likely backed up by NSF requirement which is non government but has developed methods of testing.  Every restaurant I have been involved with has been equipped with only NSF approved products. From shelves to cookware to appliances to floor and wall surface. (All cost a considerable amount more money btw) I don’t think one can find an NSF certified cast iron pot. I have seen  NSF certified  glazed ceramic pots though. Sealing is super important so when I walk with the local health inspectors they are often very picky in the construction aspect and everything sealed as effectively as practical. Seems to make  total sense and probably common sense actually.

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9 hours ago, Tyler Miller said:

 

 

 

 

Leadminimg towns in Aus .

Parents are super aware of dangers of children ingesting soil.. esp..bad effect on developing brains..

So houses are cleaned meticulously, yards are treated or covered with different stuff,  hands are washed very frequently etc etc. Windy days kids inside.

Amazing how many times folk touch lips, faces , fingers up nostrils..even....ingesting soil..a day throwing pots will give evidence of that.

Leadheads a slurring name banded around by the ill educated .

It depends a lot doesn't it.

Straw that breaks the camel's back..

If rice containing cadmium a major part of the diet...

Overall load already in the body etc...

Eat the small fry not the biggies???? Makes sense in many ways.

Hope the OP has got the info asked for.

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On 2/8/2020 at 8:36 AM, Bill Kielb said:

You couldn't use it as a plate. All of those rules would lead one to believe that unglazed terra cotta would not be allowed as a food contact material unless it was sealed with an FDA approved material.

Well my use case is one-time.  The plate is "not allowed" because it is difficult to clean and reuse .  My use- case does not require cleaning and reusing.  The fact that something is porous  makes it difficult to reuse.  But there is no reason it cannot be used at all , as long as it is not toxic.

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13 minutes ago, Preeti said:

Well my use case is one-time.  The plate is "not allowed" because it is difficult to clean and reuse .  My use- case does not require cleaning and reusing.  The fact that something is porous  makes it difficult to reuse.  But there is no reason it cannot be used at all , as long as it is not toxic.

How are you going to clean it before it's used to serve food on? They don't come out of the kiln ready to use

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21 minutes ago, Preeti said:

Well my use case is one-time.  The plate is "not allowed" because it is difficult to clean and reuse .  My use- case does not require cleaning and reusing.  The fact that something is porous  makes it difficult to reuse.  But there is no reason it cannot be used at all , as long as it is not toxic.

Can you tell us exactly what you plan to do? I think we're all a bit confused.

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Like @Tyler Miller mentioned I chose terracotta since I am culturally very comfortable with how it is used as cookware :-)  un-glazed.  I  however need to make sure it is not toxic and is "food safe" . 

Thanks to   our discussion I have some good starting points w.r.t testing clay.

I am not planning on selling cookware, I am planning on selling food, cooked+sold in clay pots.

 

Edited by Preeti

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