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mrcasey

Is Patsy Green 2 From Britt Book Food Safe?

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mrcasey    5

A member of our community studio would like to mix up a batch of Patsy Green 2 from John Britt's mid fire book.  The lithium concerns me

as does the 4% copper.  I don't have glaze software to look at the limits and I was wondering if somebody could run the numbers for me.

Also, I'd be interested in anyone's opinion about the safety of the glaze. 

Neph Sy                    44

Silica                          18.9

Whiting                    7.9

Kaolin                         2.3

Dolomite                   5.6

Gerstley Borate    12.8

Lithium Carbonate    4.8

Zinc Oxide                    3.8

-------------------------------

Copper Carbonate      4

Bentonite                          2

  

 

 

          

Edited by mrcasey
misread handwriting

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Tyler Miller    331

Even without the numbers in front of me, I'd expect the glaze to be stable-ish, just looking at the recipe.

I can tell you lithium's toxicity is pretty low.  Lithium Carbonate is used as a medication for bipolar disorder in much higher doses than what would leach out of a pot.  

 

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Min    777

Nope. Not enough silica in the glaze to make it durable. Alumina is on the low end of being adequate. Rule number one for a stable, durable, non leaching glaze is to have enough of those two things. 

Re copper and lithia; in a stable glaze that is fired to maturity and washed in hot soapy water before use, the copper might be okay but only way to tell for sure would be to have the glaze tested. Copper leaching will make foods taste funny but unless  the user has Wilson disease I believe the current literature from Dr.Carty et al shows it’s not excessively harmful. Lithia is harder to nail down, there is no agreed upon limit for it in glazes. Excessive amounts can cause both shivering and crazing on the same pot. Like Tyler said it's probably okay though.

 

green.png

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Tyler Miller    331

So, I wrote out the Segwr formulae by hand, and this is what I got:

CaO: 0.33

MgO 0.0373

K2O 0.168

Na2O 0.210

Li2O 0.041

ZnO 0.217

Si2O 2.046

Al2O3 0.314

 

A few figures were divergent from what was above, but I triple checked and I'm 100% positive they're correct.  I fiddled with different kaolins and I get a pretty similar number +/- 0.1-2

 

I'm going to say this glaze is not ideal for a bathroom sink or toilet bowl, but it's probably reasonably stable.  I trust John Britt

Edited by Tyler Miller
Miscalculated Alumina

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David Woodin    26

The glaze Al/Si is not in food safe range.   Food safe limits developed by John Hesselberth doesn't use Lithium.  The glaze as written doesn't add up to 100 %, Dolomite should be 5.6.  John Britt on page 111  says do not use on functional surfaces.  (Mid range Glazes)

David

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Tyler Miller    331

I won't push this issue much further, but I would like to point something out.

Here is a unity formula typical of borosilicate glass.  Edit: deleted original formula in favour of a more correct, and very extreme example in lab widespread use.  Original formula posted was not "lab glass"

Si2O :  11.6496

Al2O3 : 0.7350199

B2O2 : 1.6724 (!!!!!)

CaO : 0.4043

Na2O : 0.5957

Boro is the gold standard in labs.  But it doesn't cut muster for our limits.  It's fired  w a y  past fusing point to drive off gasses formed during fusing.  

Fused quartz and lime soda glass don't meet limits either (often by a long shot).  Nor do shinos, or many ash glazes or slip glazes for that matter.  

Leaching is only one consideration in limit formulas.  I tend to take them with a grain of salt.  Especially when the ones promoting them usually are trying to sell you their glaze software.  

 

Edited by Tyler Miller
Editted to use better example of divergent glass.

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Min    777

Tyler I somewhat agree with your point about "limits", think they should be used as one part of this whole business of glaze durability / safety. What I do find them useful for is getting one into the ballpark of what is likely going to be a serviceable glaze, if that is the goal. I find many glazes to be outside the suggested "limits" for flux(es) and yet still be very functional glazes. Case in point would be dolomite mattes. However, a glaze very low in silica and or alumina just isn't going to stand up. Re shinos, ash or slip glazes, I would have to question what is in them that do harm if leached out. Potassium, sodium or calcium for example I don't feel are in the same category as say cobalt, manganese or copper therefore being outside the "limits" not such a big deal. 

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Tyler Miller    331

Min,

I've done some reseaech into copper cobalt and manganese, including talking to a specialist about them--they're not the bogeymen they've been made out to be.  Manganese is the most serious of them, but mainly for us as potters, not the end consumer, with the exception of the metallic glazes its used for.

Barring Wilson's disease, Copper's really a non issue.  10 mg per day causes no issues in a healthy person for a while.

I'll compile a bibliography to back this up in a different thread tomorrow.  It's been heavily studied and when you compare the numbers to what's leached in all but the goofiest glazes, it's fine.

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bciskepottery    925

I think a main concern about leeching is that it could affect the taste or appearance of the food coming in contact with it.  Also, there can be some discoloration of the surface of the ware. 

Hesselberth and Roy adopted limits leeching for U.S. drinking water (I think) because there are no standards (except for wares used in commercial eateries that are issued by FDA).  

And, if you look at limits between H & R, Britt, Tony at Digitalfire, and others, there are variances in what they recommend.  H&R focused on durability, so their limits reflected that emphasis. 

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JBaymore    1,432
13 hours ago, bciskepottery said:

Hesselberth and Roy adopted limits leeching for U.S. drinking water (I think) because there are no standards (except for wares used in commercial eateries that are issued by FDA).  

Actually LONG before John and Ron put this idea into Mastering Cone 6 Glazes this idea was proposed by Mononna Rossol of ACTS.  Credit where credit is due. 

As Tyler is saying, the whole "toxicology" thing is seriously blown out of proportion in the online ceramic community.  It is a serious example of why the internet and the "equal" voice it give to "all" is a dangerous thing.

The biggest hazards of any of our raw materials are to US

Limit Formulas or Target Formulas are only ONE aspect of glaze development, and are a starting point.  Important but not "everything"

The ONLY way to know if a glaze is leaching something at a level of potential concern is to have it TESTED by a chem LAB. 

The only things that even need to be tested for are things that are actually toxic in the FORM that they might be in when they leach.

Not all forms of the core "chemical" are toxic.  Simply saying "copper" or "barium" is not specific enough.

Testing is only useful if your making and firing control processes are very tight (batch to batch variations in mixing and firing).

To understand this toxi stuff you need to understand stuff like orders of magnitude, ppm, dosages, LD50, TLVs and PELs, and so on.  This is HARD science and medical stuff.

It is more complex that any of us think.

If the incidence of issues from this for potters was large, then product liability insurance for potters would be WAY more expensive than it is.

best,

 

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

 

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neilestrick    1,381

I get that much of the toxicity issue is blown out of proportion, but since there are so many variables in studio ceramics, isn't it better to err on the side of safety when a glaze is borderline like this one? The best poor outcome is that you end up with an unhappy customer. At worst, you make someone very sick, and no glaze is worth that. Plus all it takes is one case of someone truly being harmed by a glaze to suddenly make our lives as potters much more difficult and expensive. What if we had to send all of our glazes off to be tested and register them with the FDA? What if OSHA inspected our studios? There endless amounts of good glazes out there, so why risk anything for this one?

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Tyler Miller    331

Neil, here's an example of how far out of proportion things are. They use cobalt metal on the wear surface of hip replacements (endoprosthetics).   That's the number 1 source of cobalt poisoning right now--hips used past their service life--because of cobalt metal being implanted in people's bodies. There's more cobalt in a shot of B12 (cobolamin) than there could ever be in a reasonably stable low fire glaze holding your tea for half an hour.  Sources to come.

Edited by Tyler Miller

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neilestrick    1,381
39 minutes ago, Tyler Miller said:

Neil, here's an example of how far out of proportion things are. They use cobalt metal on the wear surface of hip replacements (endoprosthetics).   That's the number 1 source of cobalt poisoning right now--hips used past their service life--because of cobalt metal being implanted in people's bodies. There's more cobalt in a shot of B12 (cobolamin) than there could ever be in a reasonably stable low fire glaze holding your tea for half an hour.  Sources to come.

I get it, and I'm not questioning your numbers, but we all know that it's not about actual numbers, but rather the perception of danger. I know of a  university ceramics program that was lumped into a lawsuit by a woman whose son had lung issues, because the clay dust that came home on her clothes may have contributed to the problem. Alpine Kilns was also involved in the lawsuit because the current owner of the company couldn't prove that backup insulation in the 30 year old kiln at the school wasn't asbestos. The woman had never touched the kiln, and her son had never stepped foot on the campus.

Again, I'm not questioning the validity of your numbers. In fact, it's comforting to me to know they exist. But the reality of my situation, and all people who sell hand made ceramics, is that we currently fly under the radar of Big Brother when it comes to safety regulations. When they decide to crack down and regulate us, we're all screwed.

What if you sell a mug that leaches small amounts of copper to someone with Wilson's disease? It's possible. It affects 1 in 30,000 people. That means it's possible that someone in my little suburb has it. I'm the only potter in town, so there's a chance they could buy one of my pots. And if they get sick from it and trace it back to my shop, suddenly I'm the potter who sells pots with glazes that make people sick. Or even if it doesn't make someone sick, if it makes their tea taste strange or turns the color of a lemon wedge on the lip of the mug, the damage to my reputation will be the same. The grapevine is not very good at keeping the facts straight. I once had a prominent business owner in town telling her friends that I was the 'expensive potter'. She knew nothing about handmade ceramics, and had never been to a gallery. How do you think that helped my business? I'm not willing to risk everything because I think a glaze is pretty and it'll sell.

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Tyler Miller    331

Neil, Wilson's disease sufferers take chelating agents and zinc to block uptake of copper.  If they're diagnosed and treated they're at no more risk than anyone else.  If they're undiagnosed, their multivitamin and the steak they had for dinner every Sunday was more of a culprit than the copper mug is.  It's a chronic, metabolic pathway failur, not an allergy.

Edited by Tyler Miller

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neilestrick    1,381
Just now, Tyler Miller said:

Neil, Wilson's disease sufferers take chelating agents and zinc to block uptake of copper.  If they're diagnosed and treated they're at no more risk than anyone else.  If they're undiagnosed, their multivitamin and the steak they had for dinner every Sunday was more of a culprit than the copper mug is.

You're totally missing my point.

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Tyler Miller    331

Respectfully, I think I got it.  There's a hitch in the lawsuit stories you tell.  In those cases, the failure to prove there wasn't asbestos in the kiln is a failure to prove your product is safe.  As is the kid's example with lung issues.  It's not the fact that it happened, but that they failed to prove that it couldn't. That's how those cases work.  And if an automanufacturer did that, the class action cases would be huge.  "We can't prove our seatbeat didn't exacerbate that woman's injury, though it probably didn't" isn't good enough.  That's why recalls happen when "this bolt may shear off because of y,"--because someone didn't properly approve that  batch of bolts.

It's a failure to cover all your  bases.  And that's why you have insurance and that's why you disclose what you can to your consumer.

I can say without a shadow of a doubt that the above glaze, however won't exacerate someone's wilson's because the copper pipes in their home, the foods they eat, and the multivitamins they take all contribute more copper over time.  It just doesn't work that way.  Humans just  naturally intake copper.  And effects take a while to build up.  Me knowing that is me covering my bases.  I took the time to learn about how copper can  e toxic, the amounts it can leach, and the effects it has on vulnerable populations.

Lead and cadmium are in a league of their own in that glazes can leach chronically and even acutely toxic levels into food with even casual use.  They're seriously toxic.  And that's why they're regulated.

Edited by Tyler Miller

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Min    777

 

Any of us that sell our work directly to the public would likely be able to recall a question or comment or two that leaves us shaking our heads. Over the years I’ve had several customers ask, while touching the glaze, “will this come off?” Many people are just clueless about what we make. We can be educated up the yin yang but it’s customer perception at the end of the day that  can make or break our reputation, especially in this age of social media. Joe Blow customer isn’t going to know what is in the glaze and if it’s toxic if it exhibits a changed colour or gloss. They are just going to wonder and probably not be too thrilled about it. Now bring in women of child bearing years or children, using these same pots and I’m guessing you would jump to a whole other level. 

Apologies to mrcasey for this thread going sideways from the original question. Perhaps we could start a new thread to discuss the durability issue.

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glazenerd    816

And people wonder why I only make crystalline tile. The legal term is "severability",  a nice little caveat  that Senators wrote into the law to repay their large corporate attorney donors. Which basically says if you touched a product in any shape or form from the time raw material was taken out of the ground until it lands on someone's table: you can be enjoined in a suit.  

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Tyler Miller    331

Tom,

severability means that if a part of a contract is illegal or unenforcible, the remainder is still in effect.  It's a contract law term, also used in legislation.  I could see how it could be maybe related to liability law, but it's not the phenomenon you describe.  

I'm pretty sure you're talking about joint liability vs several liability.  With joint liability being the concept at work in your example.

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The question is too complicated to answer using unity formula with theoretical materials. If you change the recipe to be inside the limits is it now food safe?

That seems as much a stab in the dark as saying a glaze is out the limits. 

 

7 hours ago, JBaymore said:

The ONLY way to know if a glaze is leaching something at a level of potential concern is to have it TESTED by a chem LAB. 

 

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glazenerd    816

Correct Tyler- my beloved I-pad wants to auto correct everything.  several liability.  I was drug into a lawsuit years ago between two land owners arguing over property boundaries. A corner of my ground touched theirs, so one attorney enjoined me in the suit. They were suing over a tract that was 1 foot by 120 foot. 

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bciskepottery    925
1 hour ago, glazenerd said:

Correct Tyler- my beloved I-pad wants to auto correct everything.  several liability.  I was drug into a lawsuit years ago between two land owners arguing over property boundaries. A corner of my ground touched theirs, so one attorney enjoined me in the suit. They were suing over a tract that was 1 foot by 120 foot. 

Whether 1 foot x 120 feet or 15 feet x 120 feet, they are all billable hours.  And the more lawyers involved, the more hours billed. 

(Full disclosure:  my daughter is a law school graduate, I work with an agency full of lawyers, and am a consultant who bills by the hour.) 

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