Source Material on Cobalt and Copper Leaching in glazed wares

[Tyler Miller]

 

So here's the deal.  I'm not a doctor, nor do I pretend to be, nor is this medical advice.  This is a list and summary of articles you can read to understand the risks you present your consumers.  And make informed rational decisions about ceramic safety and durability.

 

So, here's what I've compiled on the topic of two main sources of concern:  copper and cobalt.

 

Copper: 

 

Copper is a non-issue in glazed wares for the healthy population.  People with Wilson's disease (or other similar disorders) are the only portion of the population who will care about copper and the disease is more about cumulative effects than immediate, acute poisoning.  Diet and other factors matter more and exposure limits are currently being researched for vulnerable populations.

 

More about the disease here:  https://www.niddk.nih.gov/health-information/liver-disease/wilson-disease

 

The taste threshhold for copper in water is discussed here:  https://www.ncbi.nlm.nih.gov/m/pubmed/11124219/

 

For the healthy population, taking like 10 mg a day of copper doesn't cause issues.  Exposure to elevated levels over time discussed here 

 

https://www.ncbi.nlm.nih.gov/m/pubmed/12600855/

 

https://www.ncbi.nlm.nih.gov/pubmed/12748413

 

https://www.ncbi.nlm.nih.gov/m/pubmed/2931973/

 

https://www.ncbi.nlm.nih.gov/m/pubmed/11121720/

 

And, in the interest of balance, a case of a dude poisoning himself slowly over three years by overdoing it

 

https://www.ncbi.nlm.nih.gov/m/pubmed/10383882/

 

Now, you might be saying, "Hold on, Tyler, this is all meaningless until we know just how much copper is leached from a pot."

 

Well, you're right!  So here are two studies done on Mexican and Indian lead glazed folk pottery.  The kind of majolica-y stuff tourists love to buy and serve you food in at parties

 

Mexican pottery tested for lead, cadmium, and cobalt:

 

http://www.mdpi.com/1422-0067/12/4/2336/htm

 

Indian pottery tested for heavy metals, including copper

 

https://www.ncbi.nlm.nih.gov/m/pubmed/9397599/?i=3&from=/18472562/related

 

Here are more on lead, and cadmium:

 

https://www.ncbi.nlm.nih.gov/m/pubmed/12453733/?i=4&from=/9573626/related

 

https://www.ncbi.nlm.nih.gov/m/pubmed/9151439/?i=2&from=/9573626/related

(This one measures zinc, as well)

 

The important takeaway is that the thresholds for the highly toxic

lead and cadmium are easily reached, but less toxic metals like copper are not an issue even for taste, since the threshold for tasting the metal isn't reached in a reasonable glaze.  That doesn't mean you should ferment sauerkraut in your copper lustre raku, because that's bare metal on the surface, but we're fine with most glazes even in the ballpark of stable.

 

Cobalt is similar to copper in this respect.  It's an essential mineral--B12 has it at its core.  It's used in endoprosthetics, and loads of medical applications.  Unless you're in the industrial abrasives business or live near a toxic waste dump, (or you're a Quebecois/Belgian alcoholic living in 1964), you're probably not getting cobalt poisoning.  

 

But here's some info:

 

http://www.who.int/ipcs/publications/cicad/cicad69%20.pdf

 

This WHO bulletin shows Oc health exposure limits for cobalt and its salts (at the end)  It also cites two studies done on dust exposure from zinc silicate glazes. Page 21 onward is the important reading.  The TL;DR--wear your P100 respirator when working with the stuff, have adequate air exchange, clean up wet, and don't use more cobalt than you need.  Stuff you're doing anyway, right?  

 

To be clear, I'm not advocating careless behaviour, I'm saying inform yourself and act accordingly.  The bogeymen aren't real, but science is. I could not find a single case of Wilson's exacerbated by a copper glazed pot in the literature.  I could not find a single case of glaze based cobalt toxicity either.  It's a non issue for consumers.  

 

Also, PLEASE employ studio best practices for safety--just because your leaching copper pot won't likely hurt someone doesn't mean you're not hurting yourself in the studio.

 

I've left Manganese out of this discussion because it's been discussed to death and there's no point furthering that discussion.  There are countless studies out there to read and I hope you read some.  The collective body of evidence will inform your own studio practice and allow you to make informed decisions on behalf of your consumer.

 

I've been guilty of shaking my head at the labels on the big company's glazes, but I think they're right in what they do, after all my research.  Lead and Cadmium are what really matter, and their use is limited and regulated accordingly.

 

My own position is this:  If a glaze discolours a lemon, I have no interest in using it for any work.  It's not archival and won't stand up to time.  If I can taste metal in a liquid (based on those taste threshold studies) in a vessel, that glaze is dissolving, releasing a LOT.  That's a huge glaze chem issue and that glaze isn't a bit out of silica or alumina in a seger formula, it's fundamentally flawed beyond all serviceability.  Functional or otherwise.  But I don't rely too heavily on those formulas because the effects I like break the rules.  But so does the most stable lab glass available--fuzed quartz.  As does borosilicate and your granny's mason jars.

 

If in doubt, have your work tested.  Talk to your doctor (or better yet, get a referral from your doc to a specialist), and maybe talk to a lawyer about liability law.  Let your customers know what's in your glazes, and advise on safe use.  I include a "care and feeding" slip with things I sold at craft shows (I don't do them anymore), and have a little speech for in person sales.  If you're really paranoid, do what Health Canada recommends and render non-food safe pieces unusable by punching a hole in the bottom, or putting a metal ring through the foot ring (so a plate can't sit flat and may only hang on a wall).  Common sense and information is best.

 

Think, be actively informed, and make your decisions accordingly.  If you do that, no matter what you decide based on that, you're miles ahead of 99% of potters at the craft shows.  The vast majority have no idea what's in their premixed glazes and why.  "What's rutile? Oh, I don't use that in my work.  I just used Amaco PC-20 on that piece."  That seriously came from a potter at a show I was at.  

[mrcasey]

Thanks so much. 

[Guest JBaymore]

EXCELLENT post,  Tyler.  Thanks for this one.

[Min]

Thanks for taking the time to post this, interesting reading.

If I may just play devils advocate for a moment….

re copper

- the first study you linked to lasted for 2 months and the blood markers measured at the end of which where only from 240 participants. Not comfortable whether or not this is a large enough pool or duration?

- second study, 6 weeks duration, no info given on number of participants

- third study, 12 weeks, 7 participants

- the last study, the one on lipids, no info re length nor participants

From the article on Mexico regarding cobalt, this bit:

"Although a permissible limit for the levels of cobalt in the recipients of glass clay has not been officially mandated, it is known that this metal can be toxic to living organisms [49–52]. Therefore, a 1.5 ppm maximum permissible limit of this metal has been reported because higher levels can be related with health problems. As we can see, the levels of Co leached from containers by the acetic acid are higher than the permissible level, beginning with the first extraction and increasing with further container use, reaching concentrations of >70 ppm. Co is essential in trace amounts for living organisms, mainly in the form of vitamin B12, and is important for the functioning of red blood cells. Although it is not easily stored in the body, consumption of high amounts can cause adverse effects in lungs, heart, and skin [49–52]. It has also been shown that high amounts of Co can cause severe damage to respiratory pathways, such as degeneration and squamous metaplasia of the olfactory epithelium [29]. Thus, care must be taken with the different exposure pathways for humans because Co levels can increase to levels that pose health risks."

It’s gone 1 in the morning so I could be reading this wrong but my takeaway from this would be in these cobalt containing glazed pots there could be detrimental health consequences over time, depending on the acidity of the foodstuffs as the cobalt concentrations reached  nearly 47 times that of the articles 1.5 ppm maximum permissible limit. I might have missed it but I didn’t see data re the percentage of cobalt used in the glazes nor glaze surface (matte or gloss). (I realize this is only considering one pathway of exposure, not inhalation)

I’m all for getting educated and not being hysterical about glaze safety but I think the depth and breadth of the studies needs to be considered. Perhaps, like you said, it’s not an issue and that’s why it’s so difficult to find larger studies.

[Tyler Miller]

Min,

I do apologize for only posting abstracta to those studies.  I am too poor to pay for forum access.

The takeaway from those studies above is that the levels used are well above the taste thresholds cited in the study on that.  In order to poison oneself with copper, you would have to drink many litres of funny tasting water over a period of time greater than a few months.  An impossible scenario for us.  The copper in our hypothetical drinking water pot would run out long before it was an issue, if the person's judgment and tasting ability were compromised.

Re: cobalt,

The initial composition of the glazes and enamels is tough to find, being the blue lettered Table 1 and 2, in the body of the text, not above the captions, where it should be.

I can't figure out where they got the number 1.5 ppm from.  At best, I can surmise it came from a study on the reproductive effects on mice or a study on the behavioural effects on rats with cobalt in the drinking water at levels higher than that.

In any event, that 70 ppm came from a high number of extractions (I believe they mean 24 hour periods as per the FDA method), with 4% acetic acid just below commercial vinegar (5%).  This produces an extreme example, with unstable lead glazes that are a more immediate concern because of the other two metals studied.  Something like storing a jar of pickles with brine in a vessel for over a week.  And even then, it would only constitute a tiny increase in total body burden, in the realm of μg (micrograms) per ml, when the total body burden is in the realm of 1.15 mg.  An order of magnitude difference.

The studies that the WHO cites taken in context with this information point to an all but impossible scenario--the closest being maybe the quebec beer drinkers with cardiomyopathy--but that was cobalt sulfate deliberately added to beer.

So far as I can find Health Canada, the gov't of BC, and the EPA don't publiah guidelines for humans or wildlife on cobalt levels in drinking water. The evidence isn't there to support a  need.

Here's a 31-day study of cobalt supplementation: 

https://www.ncbi.nlm.nih.gov/m/pubmed/24283372/?i=3&from=/25629922/related

There is a 90 day study forthcoming, but not yet published.

[neilestrick]

I would like to add that while I agree that the effects from pottery are likely not a big problem, it would be wrong for us to discuss metal poisoning as though our pots are the only means of exposure in people's lives. We live in a world where we are bombarded with toxins, known and unknown, and it is our responsibility to make sure our glazes are contributing to that as little as possible. To say that leaching from our glazes couldn't come close to the known limits isn't the issue. We should avoid even being on the list of minor contributors.

[Tyler Miller]

Neil,

my buddy has haemochromatosis, retains iron like a Wilson's sufferer retains copper.  So Iron's out.  Vanadium, nickel, and chrome are out, as is manganese, and barium (obv.).  Boron can have reproductive health effects, so that's out.  Strontium's out because it's almost always contaminated with barium. Etc. You get the point

There's no such thing as a risk free glaze, just knowledgeable risk management.

I respect your passion and care--I'm sure your customers and clients see it too.  And I'm not going to force you to use pigments you don't want in glazes you don't want.  I'm just saying the risk isn't even close to what people think it is.  We all make our own choices, and I respect yours.  But reasonable compromises do exist.

[Guest JBaymore]

17 minutes ago, Tyler Miller said:

my buddy has haemochromatosis, retains iron like a Wilson's sufferer retains copper.  So Iron's out.  

Yup... there are a number of rare-ish afflictions/conditions that can possibly complicate and blur easy answers to this stuff.  Mononna Rossol has a documentation of a legal case about iron, its potential toxicity, and pottery.   Let's see if I can remember this one correctly........ 

A person (who happened to be a lawyer, If I am remembering correctly) bought a mug from a handcraft type potter.  It was his favorite mug.  Loved that mug.  He used it every day for his coffee.  He was a coffee "addict".  Had a lot of coffee from that mug every day (for a while). 

The inside was a kaki type iron saturate glaze.  The potter felt that this glaze was not rich enough in color by itself, and so used an airbrush/spray gun to spray an iron oxide wash over that kaki type glaze to give it some more "interest and depth" to the surface.  Looked beautiful.

Turns out the 'coffee addict' guy also suffered from haemochromatosis. 

You can guess the outcome of this story.

 

Just like the only way to know the amount of X leaching out of a particular glaze on a particular clay body in a particular firing cycle is to have a lab test done...........

.... and the only way to know if the results of that lab test are of concern is to compare to a medically/scientifically established "standard" that might be applicable in the case of potential uses for the object........

......... the only way to have 100% certainty to not causing harm to someone from pots we make for food purposes........ is to NOT make pots for food usage.  Which is one possible conclusion...... but not one most of us likely would want to make.

Getting a decent education on the subject, careful work practices based upon that education, decisions about what level of risk is acceptable, and then insurance or stuff like LLCs seems to be the general progression of how to deal with this if you don't want to stop making food use pots.

And saying this again.....being aware that the REAL place to be concerned about this subject is for US in the studio.  And the "real-est" hazard there is not cobalt or manganese or vanadium or copper........ it is pretty simple.  Clay and glaze dust bearing silica.

 

The lack of extended and well funded scientific/medical studies on this subject speaks volumes about the magnitude of the issue.  The cheapness of potters product liability insurance also speaks volumes.  

best,

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

 

[Guest JBaymore]

1 hour ago, neilestrick said:

I would like to add that while I agree that the effects from pottery are likely not a big problem, it would be wrong for us to discuss metal poisoning as though our pots are the only means of exposure in people's lives.

This is a toxicology concept called "Total Body Burden".   And yes, important to remember.  For us in the studio in particular. 

best,

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

[Benzine]

HOLD IT RIGHT THERE TYLER!  How exactly would YOU suggest, that I'm supposed to ferment my sauerkraut, sans my copper glaze Raku  canister (AKA the Rotten-Cabbaginator TM pending...)?

[Guest JBaymore]

There was a bit of a "joke" thread on this general subject a long while ago.   I think it was on CLAYART (when I frequented that a lot).

We talked about turning a potential liability into an asset.

SO if we make stuff that leaches stuff into foods (like coffee, tea, etc.) maybe we could USE that.  I can't remember who came up with the marketing name but it was "Nutri-mugs".  These of course would have the same caveats as many supplements have...... you know..... claims not tested by the FDA....etc.

Depressed , try our new Lithium Blue Nutri-mug.

Iron deficiency anemia?  Our Iron Red Nutri-mug is just what you need.

best,

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

 

[Benzine]

Sounds like quite the idea John!  Some potter needs to run with this, and go on "Shark Tank".

 

I have actually noticed a small uptick, in the amount of commercially made ceramic wares, showing up on infomercials.  There was one, that they marketed for cooking things, like eggs, in the microwave, and because of the "ceramic nonstick coating" it was super easy to clean!

 

[Min]

3 hours ago, JBaymore said:

 

Iron deficiency anemia?  Our Iron Red Nutri-mug is just what you need.

best,

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

 

Cast iron frying pans!  (we don't eat red meat and run towards being a bit anemic so use them to get a bit of Fe).

 

[neilestrick]

4 hours ago, Tyler Miller said:

Neil,

my buddy has haemochromatosis, retains iron like a Wilson's sufferer retains copper.  So Iron's out.  Vanadium, nickel, and chrome are out, as is manganese, and barium (obv.).  Boron can have reproductive health effects, so that's out.  Strontium's out because it's almost always contaminated with barium. Etc. You get the point

There's no such thing as a risk free glaze, just knowledgeable risk management.

I respect your passion and care--I'm sure your customers and clients see it too.  And I'm not going to force you to use pigments you don't want in glazes you don't want.  I'm just saying the risk isn't even close to what people think it is.  We all make our own choices, and I respect yours.  But reasonable compromises do exist.

I never said that what we did was, or could be, 100% safe. I never said we shouldn't use copper or iron or cobalt or chrome or nickel, etc. I said that we should do everything we can to minimize the dangers of our products.

My issue is that this is the internet, and people don't read everything as carefully as they should. They'll scan the articles, see that you said "copper is a non-issue for the healthy population", and move on to making glazes that leach. I'm simply adding to your information and trying to put it into a larger perspective. I wasn't challenging the validity of the information you posted.

[Guest JBaymore]

52 minutes ago, Min said:

Cast iron frying pans!  (we don't eat red meat and run towards being a bit anemic so use them to get a bit of Fe).

The kettle used to brew the water for Cha-no-yu (Japanese Tea Ceremony) is cast iron.  They deliberately are not coated on the inside and are NEVER cleaned with cleaners or abrasives.  They are dried, but over time, the interior rusts a bit.  The slight iron content that gets into the water as it is sitting there boiling is considered good for the taste of the Matcha.  A kettle should "season".  The older the better.

So someone with haemochromatosis could have some issues if they practiced Tea regularly.

best,

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

 

[Tyler Miller]

@neilestrick

After rereading your comments, I agree with you.  Sometimes it's easy to fall into a mode of interpreting things, esp in as rarified a means of communication as an internet forum.  Sorry about that, I will do better in the future.  Also sorry for taking so long to respond, I've been in the sticks for 8 days and my cell signal was rough--tried to log in twice to respond to you, but northern Ontario's cell towers weren't having it.

[Babs]

well here in high acid sand country where livestock get white fleshed and poorly they used to get cobalt bullets and a grinder bullet placed down the throats and so swallowed....

crops get treated with manganese zinc and copper, dolomite and more

I have been keeping my family healthy all these years by serving tea in nutri mugs, encouraging them to lick the plates ....

[Marcia Selsor]

Thanks for all the good info and discussions. The air in Montana for the last month has been so smokey from forest fires that animals were suffering and people warned to stay inside.

The chemicals we use need serious attention but it seems pollutants still can get use.

 

Marcia

[Guest JBaymore]

3 hours ago, Marcia Selsor said:

The air in Montana for the last month has been so smokey from forest fires that animals were suffering and people warned to stay inside.

Part of the concept of "Total Body Burden".  Add those sub-micron smoke particles to the silica dust us potters deal with.  This is all complex 'big picture' stuff.

best,

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

[neilestrick]

On 9/15/2017 at 9:50 PM, Tyler Miller said:

@neilestrick

After rereading your comments, I agree with you.  Sometimes it's easy to fall into a mode of interpreting things, esp in as rarified a means of communication as an internet forum.  Sorry about that, I will do better in the future.  Also sorry for taking so long to respond, I've been in the sticks for 8 days and my cell signal was rough--tried to log in twice to respond to you, but northern Ontario's cell towers weren't having it.

@Tyler Miller I'm sorry, too. I didn't mean to push so hard, and I didn't explain myself very well. I'm super paranoid about liability because it's a big deal for my business in regard to both my students in the studio and my kiln repair customers. It was also a big part of my previous job as a tech where I was responsible for glaze safety labeling. I totally understand your point, and I know the point your were making is totally valid, and I am certainly relieved that copper isn't as bad as we've all been led to believe in regards to glaze leaching.  However, while the amount of copper that could be ingested from a piece of fired pottery is more than likely a non-issue, the raw material is not, and I felt that your statement didn't address that issue or the issue of total body burden, and could unintentionally lead people astray. I did a poor job of making that clear in my original posts, and I apologize for that. The difference between raw glaze and fired glaze is a big deal, and many people do not understand that, or the safety labeling that comes with ceramic materials.

[Guest JBaymore]

8 minutes ago, neilestrick said:

The difference between raw glaze and fired glaze is a big deal, and many people do not understand that, or the safety labeling that comes with ceramic materials.

This is a huge "understanding issue" in the studio ceramic community. 

And also not understanding that using something like the word "copper" does not apply to all of the possible FORMS of "copper" and that they can have very different properties when it comes to the toxicological aspects.

Hazard to US / Hazard to Others.  Very different beasts. 

As  likely over-generalization ...... hazard to us is probably always the larger issue.

best,

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

[Tyler Miller]

@neilestrick I sortof took it as implicit that glazed wares were the topic of discussion.  I can see how the ambiguity might arise.  All sources were regarding glazed wares, except the WHO which does provide air quality standards for workers.  I'll edit my original post to reflect that.

[neilestrick]

@Tyler Miller Have you found any research on the effects of copper and cobalt on children?

[Tyler Miller]

Similar stuff.  They gave 2 mg per day of copper to infants for a little while with no effect.  I'll post the abstract under this when I find it again.

Edit:  2mg per day was incorrect, they studied water levels of 2mg/L as safe for infants (just below taste threshold--as established by above studies).

https://www.ncbi.nlm.nih.gov/m/pubmed/9523857/

"Conclusion:  No acute or chronic adverse consequences of consuming water with copper content of 31.48 micromol/l (2 mg/l) were detected in infants during the first year of life. The results support the safety of the World Health Organization's provisional guideline value for copper in drinking water during infancy."

Cobalt--the evidence of its toxicity is pretty low in the chronic, leached-from glaze situation.  Slightly different thyroid hormone levels (the zinc silicate grinders from the WHO summary) elevated red blood cells.

It's not like lead where IQ points are shaved off and studies about increased criminality exist.

[BlackDogPottery]

Would just like to mention that I believe the toxicity of iron oxide in glazes is a fraction compared to it's use in multiple cosmetics. Lipstick, eyeshadows, blushes, and whatever else are applied directly to the skin, digested, or inhaled. You get the point, very rarely do you ever hear reports on that as it would most likely be linked to lung issues than an overdose.

 

Also wonder about the effects of gold and other luster. There's plenty of dishes with rims lined in gold or silver. I'm sure if there's any way of it coming off it must be extremely minute, but it's something to think about.