Safety, Lead in TeaWare Glazes


Discussion on virtually any teaware related item.

Safety, Lead in TeaWare Glazes

Postby joelbct » May 7th, '08, 09:15

There has been some talk of lead/ other dangerous elements/compounds in teaware lately. Does anyone have any links to scientific documents about this?

Also, someone said to stay away from metallic glazes. Does this include bizen-ware? Does anyone have info on particular glazes that are bad, or is this just a case by case basis? Would be nice to know whether a teaware glaze would leak lead *before* we shell out the $, rather than buying it first and then testing it...

Likewise, a list of glazes/ firing styles that are typically safe for drinking tea would be nice too...
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Re: Safety, Lead in TeaWare Glazes

Postby chamekke » May 7th, '08, 11:09

joelbct wrote:There has been some talk of lead/ other dangerous elements/compounds in teaware lately. Does anyone have any links to scientific documents about this?

Also, someone said to stay away from metallic glazes. Does this include bizen-ware? Does anyone have info on particular glazes that are bad, or is this just a case by case basis? Would be nice to know whether a teaware glaze would leak lead *before* we shell out the $, rather than buying it first and then testing it...

Likewise, a list of glazes/ firing styles that are typically safe for drinking tea would be nice too...


Bizen is unglazed by definition, so metallic glazes should not be a problem with bizenyaki or other unglazed pottery (such as Shigaraki).

The raku question is a bit complicated. Note that American raku - the kind that usually has a metallic glaze with an iridescent sheen - has a very different composition from traditional Japanese raku (black and red). Both types of raku are made with lead, but in the case of Japanese raku, it is safe to drink from raku chawans under particular circumstances. My understanding is that American raku is generally unsafe to use for eating or drinking - that is why so many American pieces are labelled with some sort of "For ornamentation only; do not use for food" label.

On Japanese raku, the Tea Toys facts page says:

Real Raku, made by the family of Raku Kichizaemon and his 14 generations of ancestors in Kyoto and the 11 generations of Ouhi Chozaemon's family of Kanazawa is very different from the low temperature, pit-fired and dipped in all kinds of oily stuff that is called "raku" in the West.

Since the 16th century, amateur tea masters and craftsmen have made another, similar type of ceramic into teabowls, ash bowls, flower vases, incense burners, mukozuke dishes for kaiseki, etc. These ceramics are called rakuyaki in this catalog. The techniques for making them are hardly different from those used by the two "Real Raku" making families; the difference, as far as I know is the clay (not always being 3 generations old), the exact glaze formula secrets, and the generations of skill in firing.

The rakuware handled here is made with a tiny proportion of lead to make the glaze melt at the low temperatures rakuware is fired at (approx. 1000 C for black; 800 C for red; "real Raku" is fired at 1200 C and 1000C respectively). [...]

The only danger from lead in any glaze comes with prolonged holding of an acid liquid in the utensil, which will leach out the lead. This should NEVER happen in a rakuyaki teabowl, since the matcha is not acid in nature and it is in the bowl for such a short time.

One way to help keep the bowl clean in the pores is to soak the bowl for about 5 minutes before using. I heard this directly from the present Kichizaemon 15th himself. Especially in winter, if you use hot water, the bowl will not absorb the heat from the tea and even the last guest will get a drink of hot tea; too hot and the poor shokyaku [guest] can hardly drink it much less savor the flavor, so finding just the right temperature requires much experimentation. Soaking too long is a bad idea, I can say from personal experience, because the "special smell" of the clay becomes too strong. [...]

Needless to say, you SHOULD NOT use vinegar or citrus juice of any kind [in raku wares].


So, here's yet another reason for preheating the bowl with hot water prior to whisking the matcha in it :wink:

Frankly, I have never heard anyone express reservations about safety or lead levels in Japanese wares, other than the perennial question about raku. My own concerns have to do with Yixing (or Yixing-like) pottery. How do you know when a Yixing pot is safe? How can you be sure that a seller's wares are OK to drink from? The seller may be reputable, but what about his suppliers...?
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Postby inspectoring » May 28th, '08, 08:44

most of the Yixing pots appear to be made out of clay and thats it. Atleast that is what I was told but I am certain that someone will correct me here....
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Postby olivierco » May 28th, '08, 08:57

inspectoring wrote:most of the Yixing pots appear to be made out of clay and thats it. Atleast that is what I was told but I am certain that someone will correct me here....


Adding some chemicals in the clay in order to obtain the color of a better clay is a possibility
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Re: Safety, Lead in TeaWare Glazes

Postby Wesli » May 28th, '08, 11:40

chamekke wrote: My own concerns have to do with Yixing (or Yixing-like) pottery. How do you know when a Yixing pot is safe? How can you be sure that a seller's wares are OK to drink from? The seller may be reputable, but what about his suppliers...?

Yixing clay naturally has no lead in it (lead is the main problem we're thinking about, right?). Since yixing clay is known for it's porous nature, it's normally not glazed.
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Postby inspectoring » Jun 1st, '08, 22:56

so me thinks that the best way to go for a teapot/cup is to get one that has the least amount of processing?
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Postby ABx » Jun 2nd, '08, 01:51

If you're worried about such things then the main factors in safety are the glaze and texture, though it certainly wouldn't hurt to pick up a lead test kit if you're worried about lead in particular.

Here's an article on the subject that may help shed some light:
http://www.thegreenguide.com/doc/ask/china

Personally I would stay away from anything with particularly bright color glazes or, of course, metallic color. There's a lot of stuff that's officially certified as being "food safe" that really isn't. Buying tableware from local artists has, for example, been known to be risky, even when the artist was careful (I remember this being a big deal around the year 2000).

Texture is the other thing. If it has a rough surface then it can trap particles and generally harbor some nasty bacteria. This is actually what makes the majority of clays non-food safe. Yixing has a tight surface and dries off very quickly from heat, so even though it's inherently porous it's safe. This is also a reason not to use teaware that has been broken and glued or cracked.

When it comes to the talk of lead in yixing, I've really only seen this carried over from the paranoia of lead coming out of Chinese goods in general. From what I've read the lead was used in costume jewelry as a metallic paint. While that was certainly an abhorrent practice, that's a far cry from everything in China being coated in lead. While China definitely needs some better regulation, I haven't seen any credible mentions of problems with Chinese tea or teaware.
Last edited by ABx on Jun 2nd, '08, 13:29, edited 1 time in total.
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Postby chrl42 » Jun 2nd, '08, 03:11

That's an important issue I think. Considering if clay is so porous that functions directly to water other than a mere glaze.

Some yixing teapots use a method of coating paraffin or glass liquor to give a shining quality, cobalt oxide to give a green color, iron red powder for red color and many other chemicals for effects. Whereas glaze will bar the clay from affecting. I sometimes had a stomachache with using artifical chemical contained yixings, although I don't know if it was that or just bad tea..
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Postby silverneedles » Jun 5th, '08, 01:31

if very concerned one can get blood lead levels, i think >10 is bad
more important for kids who can get permanent brain damage
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Re:

Postby armin » Apr 1st, '12, 00:58

ABx wrote:Personally I would stay away from anything with particularly bright color glazes or, of course, metallic color. There's a lot of stuff that's officially certified as being "food safe" that really isn't. Buying tableware from local artists has, for example, been known to be risky, even when the artist was careful (I remember this being a big deal around the year 2000)


So we should stay away from local artists and only buy mass produced tableware from China because that is safe?
I salute your response and I'm sure all the potters on this forum agree with it... ah those ignorant local artists... they never know what they are doing...
But you will have to clarify something... if I'm in Canada and buying from an artist in China is OK because he is not local... but if I'm going to China I have to avoid the same artist because now he is local and "risky" right? Or just american local artists?
Regarding iron and metals... there is no piece of mud on Earth that has no alumina, silica or iron plus lots of other metals...
You can put bright colors on pottery using underglazes and cover them with a great transparent lead and asbestos free glaze that is perfectly food safe.
You can make unglazed terracotta (mostly a lithium feldspar) which vitrifies beautifully creating a great food safe pot ...right here... on North American Continent, by local artists...
I know this post is old, but couldn't resist...

Cheers
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Re: Safety, Lead in TeaWare Glazes

Postby JBaymore » Apr 3rd, '12, 19:04

There has been a lot of discussion of this whole subject off and on for some time on this forum. If you do searches, you'll find lots of threads dealing with the subject. There is lots of bad misinformation floating about on this subject from various sources.

As someone who teaches technical ceramics at the collge level, including sections on ceramic toxicolgy, I've tried whenever I can to "steer it" onto more accurate information and lose the both the "hysteria" as well as the "everything is fine" approach too.

Like in most things.... the middle ground of the "extreme camps" is the place where truth likely resides.

best,

......................john
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Re: Safety, Lead in TeaWare Glazes

Postby armin » Apr 5th, '12, 10:31

JBaymore wrote:There has been a lot of discussion of this whole subject off and on for some time on this forum. If you do searches, you'll find lots of threads dealing with the subject. There is lots of bad misinformation floating about on this subject from various sources.

As someone who teaches technical ceramics at the collge level, including sections on ceramic toxicolgy, I've tried whenever I can to "steer it" onto more accurate information and lose the both the "hysteria" as well as the "everything is fine" approach too.

Like in most things.... the middle ground of the "extreme camps" is the place where truth likely resides.

best,

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


Thank you J Baymore, you are perfectly right. I do believe potters are more educated this days, in our studio for example they are really keen on what type of glaze is for what. The pots are labelled accordingly and rules and regulations are followed.
I will read your posts as I am very interested in this subject.
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