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Feb 17th, '15, 22:52
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Re: Results of Yixing lead/cadmium leach test with SGS

by Tead Off » Feb 17th, '15, 22:52

Kyarazen,

I think it's perfectly fine to test the pots. No need to justify why you are doing it. With China's reputation, it's not a bad idea to be on the safe side. I think if there were some hard evidence that teaware makers were using contaminated clays for their teapots, it would be a different discussion. Cookware is another category of which I don't want to go into because we are discussing teapots. Personally, I hope you don't find any positives in testing your redware. But, it only serves to strengthen my belief that pre-90's clay is what I will continue to look for and use, as I do now, as far as Yixing goes.

Feb 17th, '15, 23:11
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Re: Results of Yixing lead/cadmium leach test with SGS

by xiaobai » Feb 17th, '15, 23:11

steanze wrote:Good point, it can be useful to start from the question of how much of these minerals there is in tea.
http://www.researchgate.net/publication ... tamination
http://www.ncbi.nlm.nih.gov/pubmed/16118651
http://www.tandfonline.com/doi/abs/10.1 ... OQJ_81Gh5Q
Of course, that is an interesting subject by itself and deserves a thread of its own. That tea may contain all kinds of contaminants from the soil where it is grown, the water that it receives, et cetera. is well-known.

I bought one sheng cake from Yiwu that came with a laboratory test in it stating the amounts of lead, copper, etc. The amounts were small, but not entirely negligible (certainly below the limits, but not well below them). And this is a tea from Yunnan, I can't imagine what may be in green teas like Longjing from Hangzhou...

However, the issue being discussed here is whether we are unintentionally adding more stuff to what is already in the tea because we (like to) use certain types of tea ware...

Feb 17th, '15, 23:22
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Re: Results of Yixing lead/cadmium leach test with SGS

by xiaobai » Feb 17th, '15, 23:22

kyarazen wrote:
A caveat though, i had seen reports in the chinese forums that some pots were tested to leach 0.04-0.06mg/L lead, almost at, or below the minimum acceptable detection limit of ICP-AES (0.1ppm). although I used GF-AES, which gives an mdl of 5-10ppb for lead, perhaps the most obsessive compulsive should consider picking a grain of clay from a discrete area i.e. inside the spout or internal filter area for ICP-MS...

in one's blood, if 0.1ppm of lead is detected, it may be worthwhile to seek clinical attention.
Kyarazen, did your tests include cadmium in addition to lead?

Feb 18th, '15, 02:11
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Re: Results of Yixing lead/cadmium leach test with SGS

by xiaobai » Feb 18th, '15, 02:11

Tead Off wrote: Personally, I hope you don't find any positives in testing your redware. But, it only serves to strengthen my belief that pre-90's clay is what I will continue to look for and use, as I do now, as far as Yixing goes.
Although the concern for environmental pollution may be less of an issue for
pre-90s pots, I do not see an objective reason why they could be considered
completely safe.

For instance, as pointed out by Kyarazen, in the past some Yixing pots used to have leaded glazes. And, as it has been pointed out elsewhere on this forum, many of those pre-90s clays were also mixed with oxides and the
oxide production/purification technology of the time was not as sophisticated as it is now. Who knows what dangerous pottery
practices were in use in the old times.

Therefore, although they can be considered a priori safer, to the best of
my knowledge, there as little test data known for those clays as for modern clays.

Nevertheless, I do not want to imply that those old clays were, in general, less pure and authentic. I also believe they are and I have been seeking them out too. However, the only way to be absolutely sure of their safety is to test at least a few of them. :roll:

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Feb 18th, '15, 03:42
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Re: Results of Yixing lead/cadmium leach test with SGS

by Tead Off » Feb 18th, '15, 03:42

xiaobai wrote:
Tead Off wrote: Personally, I hope you don't find any positives in testing your redware. But, it only serves to strengthen my belief that pre-90's clay is what I will continue to look for and use, as I do now, as far as Yixing goes.
Although the concern for environmental pollution may be less of an issue for
pre-90s pots, I do not see an objective reason why they could be considered
completely safe.

For instance, as pointed out by Kyarazen, in the past some Yixing pots used to have leaded glazes. And, as it has been pointed out elsewhere on this forum, many of those pre-90s clays were also mixed with oxides and the
oxide production/purification technology of the time was not as sophisticated as it is now. Who knows what dangerous pottery
practices were in use in the old times.

Therefore, although they can be considered a priori safer, to the best of
my knowledge, there as little test data known for those clays as for modern clays.

Nevertheless, I do not want to imply that those old clays were, in general, less pure and authentic. I also believe they are and I have been seeking them out too. However, the only way to be absolutely sure of their safety is to test at least a few of them. :roll:
Most oxides added to clays are not toxic. I also never use glazed Yixing so not a concern for me. Of course, there can be exceptions to every supposition, I'm not too concerned about the older pots. I don't have to be absolutely sure about anything. :-)

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Feb 23rd, '15, 06:57
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Re: Results of Yixing lead/cadmium leach test with SGS

by chrl42 » Feb 23rd, '15, 06:57

Tead Off wrote:Personally, I hope you don't find any positives in testing your redware. But, it only serves to strengthen my belief that pre-90's clay is what I will continue to look for and use, as I do now, as far as Yixing goes.
Looks like nowadays it's pretty common to add preservatives in Yixing clay, when the clay is stored for decades, a potter can be darn hard to soften it to reuse or clean the moulds grown on it. I also heard they use hydrochrolic acid to purify Zhuni clays..but this just 'heard',

not that preservatives in the clays can be bad for my health..it's freaky though.

Feb 23rd, '15, 07:19
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Re: Results of Yixing lead/cadmium leach test with SGS

by xiaobai » Feb 23rd, '15, 07:19

"Hydrochloric acid" (HCl) -if I understand correctly what you mean- is what it used to be called "Aqua regia".

We used it very often when I was a kid to clean clogged pipes
in kitchen sinks and toilets. It is a very corrosive and irritant liquid
and one has to be careful when manipulating it. When mixed
with metals, give rise to salts like NaCl (common table salt).

Hard to tell what kind reaction it will produce when mixed with clay,
but most likely various kinds of chlorides, like FeCl2, CaCl2, etc. This should
be rather stable salts even at high temperatures, although by
pyro-hydrolysis FeCl2 will become Fe2O3 (that is iron III oxide).
But I am no expert... :)

Oh, I forgot to add that HCl is also part of your gastric acid...
http://en.wikipedia.org/wiki/Gastric_acid :mrgreen:

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Feb 23rd, '15, 07:34
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Re: Results of Yixing lead/cadmium leach test with SGS

by chrl42 » Feb 23rd, '15, 07:34

Thanks for interpreting, really appreciate it. :wink:

Mar 6th, '15, 04:07
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Re: Results of Yixing lead/cadmium leach test with SGS

by xiaobai » Mar 6th, '15, 04:07

Tead Off wrote:Kyarazen,

But, it only serves to strengthen my belief that pre-90's clay is what I will continue to look for and use, as I do now, as far as Yixing goes.
Interesting statement coming from a vendor who also sells modern Yixing... Or are you planing to start selling pre-90s pots only?

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Mar 6th, '15, 05:22
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Re: Results of Yixing lead/cadmium leach test with SGS

by Tead Off » Mar 6th, '15, 05:22

xiaobai wrote:
Tead Off wrote:Kyarazen,

But, it only serves to strengthen my belief that pre-90's clay is what I will continue to look for and use, as I do now, as far as Yixing goes.
Interesting statement coming from a vendor who also sells modern Yixing... Or are you planing to start selling pre-90s pots only?
I don't ordinarily sell Yixing pots from any era. The ones that I did sell were special ordered by a Thai vendor here from a workshop in Yixing that he has a close relationship with. The ones you see on my site have been out of stock for quite some time. It is not a business that I wish to pursue. Too much controversy with modern Yixing.

For my own use, I look for pre 90's Yixing. I also use other pots that are modern from Japan and Korea.

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