Chance of Heavy Metals in Hagi Glaze?

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bebop8
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Sun May 09, 2021 7:01 pm

I recently got really into tea but lack teaware. I stumbled onto this used Hagi kyusu and was charmed by it, so I went ahead and bought it along with some used Hagi yunomi (1, 2) that seem to match it well enough.

Now I'm trying to wrap my head around sterilization and wondering the likelihood of any heavy metals leeching out of the glaze. I was thinking of heating them in water (as outlined here) as it sounds like that will kill any and all pathogens, then using a water testing kit to try and detect heavy metals, but not sure if testing would be effective or even necessary. I do see mention that heavy metals in glaze is not much of a concern with porcelain due to high firing (and as long as it's not a decorative overglaze), but not sure how applicable that is to these pieces (can't tell if they are porcelain, stoneware, earthenware, high fired, low fired or what). Id hate to spend ~$25 for a testing kit unnecessarily, especially if it's ineffective, not to mention that drives up the cost of my used budget teaware to the point where I could have bought brand new ones.

If anyone has any info/suggestions regarding the above, or who made this teaware, or caring for my first teaware purchase, or any info really, I would be very interested and appreciative. Not even positive what one would call the teapot; I'm thinking it's a Hagi kyusu with a celadon glaze and a hohin style spout (as in, it's a kyusu and not a hohin because it has a handle right?), but correct me if I'm wrong please. Thank you.
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Victoria
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Sun May 09, 2021 7:33 pm

Welcome to TeaForum @bebop8. All three pieces look pretty contemporary so I wouldn’t be too concerned about heavy metals. Not much crazing either so a simple hot bath with some baking soda paste rubbed with your finger or a soft cloth should be fine, followed by a distilled vinegar wash. Regarding cleaning your Hagi and other information there are a few Hagi threads that you might refer to;

Hagi

Cleaning Hagi Houhin - Advice Needed

Hagi ware Absorption of Colour/Odor

Odor from a Hagi cup
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bebop8
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Sun May 09, 2021 8:35 pm

Victoria wrote:
Sun May 09, 2021 7:33 pm
Welcome to TeaForum bebop8. All three pieces look pretty contemporary so I wouldn’t be too concerned about heavy metals. Not much crazing either so a simple hot bath with some baking soda paste rubbed with your finger or a soft cloth should be fine, followed by a distilled vinegar wash. Regarding cleaning your Hagi and other information there are a few Hagi threads that you might refer to;

Hagi

Cleaning Hagi Houhin - Advice Needed

Hagi ware Absorption of Colour/Odor

Odor from a Hagi cup
Thank you Victoria. I appreciate the info, it put my mind at ease. I will read through those topics and will definitely do that to clean and sterilize the teaware when it arrives.
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LeoFox
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Mon May 10, 2021 8:09 am

Regarding heavy metal testing, I am sorry to say that most of the testing kits sold out there for consumers are not very precise. Even those that are "epa" certified just means they are above 60 or 70% accurate. Also, these kits are designed in this way: they allow for higher false positive to decrease false negatives. Additionally, they are mostly not designed for ceramics but for paint dust

The better way is to use a spectroscopic method, which would require more cost and sending the item or some scraping of the item away to a facility with the instrument. Even then, such facilities may not have fully validated methods.

Some question to ask yourself:

What heavy metals are you concerned about? What are their phase transition points and do you think at the high firing temps used, they would still be in the piece? Think about worst case firing conditions (ie low temps, and kilns that previously fired items with heavy metals)

What is the worst case scenario in terms of leached amount?

How does that compare to eating something like a piece of tuna?

Note I am not discouraging you from testing but to encourage you to think systematically about the risks involved.
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mbanu
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Mon May 10, 2021 10:11 am

Lead glazes are sort of the asbestos insulation of teaware, in that they cause a lot of anxiety because they seem to be in so many old items. I think what causes extra anxiety is that conceptually why there would be asbestos is easier to understand than why there would be lead, as most people don't really get what lead does pottery-wise.

The big thing to remember is not to surprise the potter -- a lot of times issues related to lead poisoning happen when someone uses a pot in an unexpected way. A good tea-related example was someone who decided that since kombucha was a tea, they should brew kombucha in a teapot. While there are acid-safe glazes, they weren't normally used on teapots because potters assumed a person would be just putting tea inside them, rather than something acidic like kombucha, and that it would only remain in the pot for a few hours at most, not for several days. A ceramic jar designed for holding vinegar on the other hand would have held up happily and there would not have been any issues. (This "don't surprise the potter" issue also tends to make me uneasy when it comes to teapot cleaning tips, as the pot is introduced to a variety of substances a potter would not have been thinking about.)

Secondly, don't allow it to become a "lurking horror". A person suffering lead poisoning will develop signs and symptoms that can be identified, such as a Burton's line along the gums.

Another thing that can help is to try to understand the basics of ceramics and pottery. You don't need to be able to make them, but being able to follow the logic of when, why, and how a piece is glazed can make it easier when confronted with a finished teapot to guess how it was made.
faj
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Mon May 10, 2021 10:46 am

mbanu wrote:
Mon May 10, 2021 10:11 am
The big thing to remember is not to surprise the potter
That is a bit like saying, about lead-based paint, "don't surprise the house painter".

Sure, it is always best to use items in the way they are intended. Maybe there was a "safe way to use lead-based paint", yet those paints were prohibited because the presence of lead in living spaces is inherently unsafe. Real life does not always follow user manuals.

Ideally, makers should expect their items will be used in unexpected ways. "Don't poison the buyer" is a safer approach for consumer items, I would say.
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mbanu
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Mon May 10, 2021 11:18 am

faj wrote:
Mon May 10, 2021 10:46 am
mbanu wrote:
Mon May 10, 2021 10:11 am
The big thing to remember is not to surprise the potter
That is a bit like saying, about lead-based paint, "don't surprise the house painter".

Sure, it is always best to use items in the way they are intended. Maybe there was a "safe way to use lead-based paint", yet those paints were prohibited because the presence of lead in living spaces is inherently unsafe. Real life does not always follow user manuals.

Ideally, makers should expect their items will be used in unexpected ways. "Don't poison the buyer" is a safer approach for consumer items, I would say.
With lead paint, there were a few surprises that caught folks off-guard. The first was that someone would paint a room and then never paint it again, allowing the old paint to become cracked and chipped while the room was still in daily use. The second surprise built on the first, in that small children would eat the chips because they tasted sweet. It was a cascading failure caused by not identifying the level of neglect that the paint would need to deal with, if I understand correctly.

With teapots many of the surprises are due to being unable to "future-proof" a pot. An example here is the split between dishwasher-safe or microwave-safe ceramics and those that are not. I suspect that it was not that they were being careless and allowing the buyer to hurt themselves, but that the requirements would have seemed fantastical at the time the pots were made. "I know your teapot cleans well in soap and water, but it must be made to withstand a lye bath in a 'dish-washing machine'-" or "I know this is a fine earthenware pot with very pretty gilding along the edge of the rim and spout that helps it to resist chips, but it will be placed in a machine that excites water molecules, so this pot would become uncomfortably hot, and the metal gilding will cause trouble with something called a magnetron-" :)
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LeoFox
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Mon May 10, 2021 11:25 am

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bebop8
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Mon May 10, 2021 8:57 pm

LeoFox wrote:
Mon May 10, 2021 8:09 am
Regarding heavy metal testing, I am sorry to say that most of the testing kits sold out there for consumers are not very precise. Even those that are "epa" certified just means they are above 60 or 70% accurate. Also, these kits are designed in this way: they allow for higher false positive to decrease false negatives. Additionally, they are mostly not designed for ceramics but for paint dust

What heavy metals are you concerned about? What are their phase transition points and do you think at the high firing temps used, they would still be in the piece? Think about worst case firing conditions (ie low temps, and kilns that previously fired items with heavy metals)

What is the worst case scenario in terms of leached amount?

How does that compare to eating something like a piece of tuna?

Note I am not discouraging you from testing but to encourage you to think systematically about the risks involved.
Thank you for the detailed info regarding poor testing kit accuracy/regulation and high false positives. I am glad to know they are of dubious accuracy and not for this use case before wasting time and money on them. A ~30% margin of error is not acceptable.

Excellent points to consider. Frankly I was struggling with that kind of systematic thinking regarding the risks, mostly due to lack of knowledge with ceramic glazes. Starting with a worst case scenario vs phase transition points and comparing to typical environmental exposure is a smart idea.

Lead and cadmium seem like they were common additives. Manganese dioxide is sometimes used too it seems , but only in black metallic glazes. Having briefly looked at glaze recipes it seems like lead risk is mitigated at cone 6. I'll gather more data and go from there, and share what I come up with. I'm not terribly concerned given Victoria's response, but it will be good to gather more knowledge to know what to look out for when buying pottery in the future.

The FDA links seem useful indeed, looking at them now. Thank you again for your detailed response. I have enjoyed reading your reviews of oolongs as well, in particular looking forward to trying TGY again after reading your review; the first time I tried it (a Verdant Tea sample of Master Zhang's 2020 autumn, traditional Anxi TGY) was highly enjoyable yet left me wanting just a tiny bit, lacking potency, but perhaps ~5g per 6oz/177ml (per the directions) was not enough leaf.
mbanu wrote:
Mon May 10, 2021 10:11 am
Secondly, don't allow it to become a "lurking horror". A person suffering lead poisoning will develop signs and symptoms that can be identified, such as a Burton's line along the gums.

Another thing that can help is to try to understand the basics of ceramics and pottery. You don't need to be able to make them, but being able to follow the logic of when, why, and how a piece is glazed can make it easier when confronted with a finished teapot to guess how it was made.
Well said. I will have a look at symptoms of various heavy metal exposures so as not to have it become a "lurking horror."

Unfortunately even with several years experience with ceramics, the only mentions of glazing and firing (if I recall correctly) amounted to selecting premixed "food safe vs not food safe" glaze/overglaze depending on the piece and (broadly speaking) to "expect breakage in the kiln". I wonder if I still have the course books; there could be data regarding glazes in them that was not covered in the classes. Hmm, not among my other books (lost to mold last year I think), but will look further.
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LeoFox
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Mon May 10, 2021 9:29 pm

@bebop8 glad you found that helpful :D

To get a sense of safety limits, you may like this:
https://database.ich.org/sites/default/ ... 9_0322.pdf

Of course this is for pharmaceuticals but you can get a sense of how limits are set with that document

And thanks for mentioning my oolong reviews! I Look forward to seeing yours on that thread!
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bebop8
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Mon May 24, 2021 9:45 pm

The teaware arrived today. Quicker than I expected of Japan Post, especially given the (seeming) current strain on them and that I ordered it before the Japanese holiday week. It was packaged well and as expected, except for 1 of the yunomi.

The clay cannot be scratched with a fingernail, so it appears hard enough that it was fired to at least the stoneware temp range. A celadon glaze recipe I found purports that lead is not an issue (with that particular formulation at least) when fired to cone 6, and it seems they were fired roughly in that ballpark anyway.

The glaze appears glassy, hard, and uniform (with the exception of a small crack/chip on 1 of the yunomi that goes through to the underlying clay), so leeching potential appears low. I was surprised that the crazing appears entirely covered (save for the aforementioned chip) with a hard clear glaze.

Being that they appear to be more modern pieces (as Victoria stated), and that celadons are high fired usually with just a bit of (primarily) iron oxide (albeit lead in celadon is not unheard of), coupled with the well fired clay and solid glaze, I'm not concerned. One would also hope that when a potter is deliberately creating a vessel with crazing that they would not be so foolish as to use heavy metals or other non food safe materials in the glaze, but I guess I can't take that for a given either.

As for the slightly chipped yunomi (visible as a black dot in the red area), I'm not sure at this point if I'll keep it or what...it is a very tiny chip, so I'm leaning towards keeping it at the moment. I'm primarily concerned that the chip will expand during cleaning/use causing the yunomi to break into pieces; I would love to hear anyone's thoughts on the matter. It does seem at least like the seller tried to disclose it via a closeup picture, but that the resolution was insufficient to capture it.

Save for the chip, the teaware is pretty immaculate, even appearing unused, but tomorrow I'll clean them to be safe and hopefully have time to enjoy them. I may run a glaze durability/leeching test on the yunomis, but likely I won't. I will probably just taste hot water left in the teaware and see if it has any negative effect on flavor, particularly being mindful of any metallic flavor (indicative of possible lead leeching).

I will share the results of my looking into toxic compounds leeching from glaze soon, in that it might help someone, but at this time I'm not quite ready to do so as there are a few points I need to look into further. In the meantime, for those interested in such things, this is a good, relevant study I found (that I'm still wrapping my head around, to be honest): https://researchcommons.waikato.ac.nz/b ... sAllowed=y
LeoFox wrote:
Mon May 10, 2021 9:29 pm
bebop8 glad you found that helpful :D

To get a sense of safety limits, you may like this:
https://database.ich.org/sites/default/ ... 9_0322.pdf

Of course this is for pharmaceuticals but you can get a sense of how limits are set with that document

And thanks for mentioning my oolong reviews! I Look forward to seeing yours on that thread!
That pdf has been a useful resource indeed LeoFox, thank you.
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debunix
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Mon May 24, 2021 11:10 pm

That doesn't look like a chip, but rather like a tiny imperfection in the glaze, something that happened during firing. It's a beauty spot.
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bebop8
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Tue May 25, 2021 12:04 am

debunix wrote:
Mon May 24, 2021 11:10 pm
That doesn't look like a chip, but rather like a tiny imperfection in the glaze, something that happened during firing. It's a beauty spot.
A beauty spot is a good way to look at it. You're probably right that it happened during firing. Certainly I feel more enamored with the piece the more I hold it; I think I'll just enjoy it and hope for the best. Thank you for sharing your thoughts, I appreciate it.
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debunix
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Wed May 26, 2021 2:46 am

I have a twin pair of blue Yamane Seigan cups that I bought a few months apart—the second one wasn’t listed when I spotted and bought the first. I bought the second one in part because the first one has a little bit of exposed clay on the inside, and I sort of resented it as a defect. When the second cup arrived, I was surprised to realize that tiny unglazed spot added hugely to the personality of the piece, and the second cup gets much less use than the first.
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bebop8
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Wed May 26, 2021 8:45 pm

@debunix I see Yamane Seigan makes gorgeous cups. The glaze on this one reminds me of the night's sky.

Yes things like that are often quite charming and add character. I was concerned the tiny flaw would grow into a structural crack and the yunomi could eventually break apart, yet in retrospect there's no reason to believe that would happen given how small it is :oops: It's probably about as innocuous as crazing.
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