Results of Yixing lead/cadmium leach test with SGS

[William]

Thank you for sharing this experience with us!

[JBaymore]

Lead is not a commonly used flux in the development of clay bodies.....would be quite problematic....toxicity issues for the potters aside. Potters would ne NUTS to deliberately add lead compounds to clay bodies that they are handling.

Why anyone would think that there would ever be cadmium compounds present in this type of ware is an interesting question. Not something that would have any practical application here at all.

If there were any lead compounds or cadmium compounds present in such clays.... (or any clays from anywhere) it would have to be from trace minerals in the processing operations or from environmental contaminants being acquired from the mining operations (god knows what is settling out of the air in China into the ground). Or from un-cleaned processing equipment that handled other minerals.

Also note that lead and cadmium are the only elements regulated in the USA in ceramic wares via the FDA and the State of California relative to leaching issues. They typically are used in GLAZES not clay bodies. Lead oxide is a flux acting on silica (SiO2 - main glass former in glazes), and cadmium compounds are used as colorants ..... mainly producing bright reds and oranges. Cadmium, unless encapsulated in a zircon crystal matrix, is quite fugitive at high temperatures...... it is used in low fire wares mainly... like overglaze enamels (China Paints).

There are other compounds that are potentially (not necessarily actually) toxic also besides lead and cadmium. Some of these can show up in clay bodies FAR more likely than lead or cadmium. With the typical colorations of Yixing-type clays, I'd be more concerned about hexavalent chromium and manganese compounds being there in some colorations of clay. And very slightly possibly (hopefully) tiny amounts arsenic compounds as trace elements coming in with other minerals.

As is so importantly and accurately noted above...... the amount of any toxin leached and the amount of that potentially consumed is also a factor in accurately establishing if there is any real concern. See the US EPA drinking water standards for comparing any tea containing leachate to the relative potential danger present in your cup of tea.

As a college ceramics professor who teaches about this technical stuff...... you got results that I would have expected from such testing. Good job in doing the "service to the field" here by sharing these results.

best,

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

[wert]

Lead is not a commonly used flux in the development of clay bodies.....would be quite problematic....toxicity issues for the potters aside. Potters would ne NUTS to deliberately add lead compounds to clay bodies that they are handling.
*snip*

Thank you for sharing your expertise on this subject. It is certainly great to hear from someone who has long and practical experience.

In the context of yixing, lead comes mainly from the ducai (external enamel), which is very seldom seen in modern works. As John had mentioned, manganese, cobalt, chromium and iron oxides are however, commonly used to achieve the colours on yixing. When overdone, they are what we called, chemical pots.

[kyarazen]

I am going tomorrow to SGS to collect my pots, so I will ask them for further details about the calibration and the MDL.

did they clean the pots up after testing? i had an AES at a former workplace where all my selected wares so far tested negative for lead. had to use 4% acetic acid on all of them for the leach testing though, did leave a smell in some for a while

[ryancha]

There are other compounds that are potentially (not necessarily actually) toxic also besides lead and cadmium. Some of these can show up in clay bodies FAR more likely than lead or cadmium. With the typical colorations of Yixing-type clays, I'd be more concerned about hexavalent chromium and manganese compounds being there in some colorations of clay. And very slightly possibly (hopefully) tiny amounts arsenic compounds as trace elements coming in with other minerals.

John, Thanks for this fascinating information. Can you elaborate a bit more. I'm not quite sure what you mean in calling them "potentially (not necessarily actually) toxic" (i.e. we have no idea one way or the other; we have good reason to be suspicious that they are toxic but aren't entirely sure; etc)

Are yixing something you feel comfortable using? Would advise against using certain (which?) colorations?

Thanks for the info!

[steanze]

+1, I wonder what you think about hei ni pots - which have added manganese oxide...

[xiaobai]

John: Thanks a lot for sharing your experience and opinion here.

However, let me clarify the origins of my concern. As you explained above, no sensible Potter would deliberately add Lead or Cadmium to his/her clay.

My main concern has to do with the environment in which the pots are produced. Anyone who has travelled enough to China is aware of the huge environmental toll that the industrial development has taken on the Country since the 1980s.

In particular, Jiangtsu Provice and Yixing city have been hit pretty badly: Southern Jiangtsu is one of the main centers for the Chinese Chemical
Industry. Those industries have been heavily polluting water and soil in the area for decades. For instance, the Taihu Lake, which many cities like Yixing use as one of the supply sources for fresh water, nowadays contains loads of heavy metals, amongst other toxic substances.

If you are not aware of the seriousness of the problem, please read here:

http://e360.yale.edu/feature/chinas_dir ... rops/2782/

for a news report or here

http://en.cnki.com.cn/Article_en/CJFDTO ... 502011.htm

for an example of academic research, out of many.

Therefore, the concern is not that the pottery Industry in Yixing may be intentionally adding toxic stuff to their clay. After all, no potter would like to work with a clay that may diminish the quality of the final product and harm his/her customers. The concern is that the people involved may not be aware of it, unless they conduct tests (some of them actually do). Of course, there are also some greedy people who do not care, and are responsible the so-called 'chemical pots' that Wert has mentioned above.

It is also important to remember that a large faction of the clays used for teaware need to undergo aging after they are obtained by milling the ore and the resulting powders are mixed with oxides to obtain certain types of colors. The clay must be kept moist during the aging process. If the clay gets contaminated during the early stage of the processing by water from contaminated sources (e.g. the Taihu lake) or by mixing with impure oxides, you will end up with toxic piece of clay ware that may leach heavy metals. I do know how serious the problem is because the Yixing industry, as many other things in China, is not particularly regulated and/or transparent about their practices and quality control.

Nevertheless, that toxic clay ware exists is well documented, not only by a series of now famous CCTV documentaries on the Yixing pottery industry, but also by research conducted elsewhere on cheap imported Chinese (unglazed) clay ware.

But let me return to issue of clay aging. As a researcher with a PhD in Surface Physics, I know well that, given enough time, heavy metal ions will diffuse thought its surface into any material. They can also form relatively complex and stable compounds, as their outer shell electronic structure allows for many possible valence states: in other words they are extremely (chemically) reactive. This is why the heavier the element the more likely it to be very toxic. A good example is Plutonium, whose extremely high toxicity has nothing to do with it being radioactive (that is, having an unstable nuclear state), but with the fact that the electrons in its outer shell can easily form chemical bonds with almost anything.

Now, the problem of how those heavy metal ions interact with the kaolin, quartz, and mica, which are the main components of Yixing clay is probably poorly understood. This is a rather complex system, and it will probably be very difficult to understand it on a microscopic basis without extensively resorting to experiments and measurement.

Experimentally, it only takes a Google search to learn that Kaolin, for instance, is a good sorbent for heavy metals, to the extent that clay is a good candidate for removing heavy metals from contaminated waters, e.g.

http://link.springer.com/article/10.102 ... 023#page-1

or

http://www.academia.edu/6113926/Clays_i ... avy_metals

Thus, to summarize, I think there are reasons for concern. Certainly not about the pottery produced in 1st-World countries like the US, Europe, or Japan, where this industry is well regulated, the standard sources of water and oxides are relatively clean and safe, and Food safety inspections are regularly conducted by Government agencies and Consumer associations. Unlike those countries, the situation in China is, to be best of my knowledge, far from clear and I am glad to see that I am not the first participant in TC that has tested his teaware.

[xiaobai]

I am going tomorrow to SGS to collect my pots, so I will ask them for further details about the calibration and the MDL.

did they clean the pots up after testing? i had an AES at a former workplace where all my selected wares so far tested negative for lead. had to use 4% acetic acid on all of them for the leach testing though, did leave a smell in some for a while

No, they did not. My pots now smell of acetic acid. I have been cleaning them since this morning.

But like everything else in life, "No pain, no gain"

Hopefully, the smell will go away after a few gongfu sessions.

[mcrdotcom]

Have you done a control on your water (from whatever source you use), especially in the test you bought from Amazon?

[xiaobai]

Have you done a control on your water (from whatever source you use), especially in the test you bought from Amazon?

No. I use bottled mineral water, which should be lead/cadmium free.

In addition, I tested two different pots with the kit. One was a clear negative. The other borderline, but probably negative as well.

SGS use uncontaminated water and have obviously calibrated their spectrometer to remove any possible solvent signal.

[kyarazen]

SGS probably used milliQ water.. which is RO water. at least i routinely do anyway..



btw...

milliQ water is strangely quite nice for tea!

[JBaymore]

xiaobai,

Thanks for the link to that second article. Enjoyed reading it.

Great stuff in your postings.... important for folks to be aware of this stuff........ and thanks for sharing it.

Having been in Yixing recently (lecturing there) I'm somewhat aware of the environmental and production situation there....... that is why I mentioned the 'contaminants factor' as being the likely issue in my other posting. I've posted some "revelations" about the real nature of the somewhat mythical and idealized Yixing elsewhere in these forums before...... trying to educate a bit. Yixing is not what most think it is, looking from afar.

Personally.. the only Yixing pieces I have and do use are quite higher-end (artisanal and price-wise) than what is often discussed here. Hopefully decent pedigree and care in clay production......but in the end..... who knows (unless tested, as you have done). A lot of the less expensive stuff that is getting produced there in Yixing is of "questionable" issue as to the nature of the materials/processes utilized.

While the ceramic arts practice and history there is an incredible 'lure' for me, the physical environment there is one reason that I have not taken up pursuing the standing offer of a guest professorship I have at Wuxi Institute or Arts and Technology; short term visiting is one thing... I can't imagine living there for an extended period, health-wise. I feel for those people. They do not have the luxury of that choice. (However, I'm taking students to Jingdezhen and Yixing next October though... short term.)

I spend a lot of time in Japan... and here is another 'interesting' factor that people likely are not aware of outside of people who are 'in the field'. After the meltdown at Fukushima, the wind deposition patterns dropped a lot of radioactive materials into the area of Mashiko... one of the major pottery centers. The potters there were advised that they could not use fire wood for their kilns from that area until further notice (still banned) because the fly ash was concentrating the radioactive residue into the shizenyu (natural ash glaze) on the works. In the typical culture of Japan .... hopefully most potters are complying.

I will be very interested to see whatever more work you do on this study.

best,

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

[mcrdotcom]

SGS probably used milliQ water.. which is RO water. at least i routinely do anyway..



btw...

milliQ water is strangely quite nice for tea!

You used milliQ for making tea? XD Expensive tea

[JBaymore]

Can you elaborate a bit more. I'm not quite sure what you mean in calling them "potentially (not necessarily actually) toxic" (i.e. we have no idea one way or the other; we have good reason to be suspicious that they are toxic but aren't entirely sure; etc)

Toxicology is a complex subject. Unfortunately some stuff has not really been studied. In other cases there are variables that can affect the answer.

I kid with my students that the correct answer to any question about ceramics is, "It depends".

The toxicity of a substance often depends on the form (chemical combination) it is in. In the ceramics field people often talk of "barium" as being really toxic. For a great example......... barium carbonate, which is often used as a ceramic glaze mixing raw material, is a quite toxic substance upon ingestion. It is the active ingredient in some rat poisons. But barium sulfate is the stuff that the doctors will have you drink as a contrast medium on xrays for something like an upper GI series. Both are "barium".

If a glaze is properly formulated and (in particular) FIRED, the raw material barium carbonate decomposes to barium oxide, which is a flux acting on silica, and carbon dioxide gas, which goes off in the effluent from the kiln. If that is the case, the BaO becomes involved in the glaze melt, and is somewhat 'tied up' in the glass's molecular matrix (association) of the glaze.

BUT....... if the firing is not done correctly, some of that finely ground barium carbonate power raw material in the glaze batch does not decompose as intended, and remains as tiny "lumps" of barium carbonate floating in the melted glaze. Those lumps are not well tied into the glass structure, and also are in a known toxic form.

In the first case above, it is POSSIBLE that some barium based material might be leached out of the glass into a strong acid or base solution, given enough surface area and contact time. But it is unlikely. And it is not necessarily in a toxic form either.

In the second case however, that possibility is much greater.

How do you know? You don't, without testing. You are depending on the technical skills and knowledge of the potter.

But then we also get to the questions of intensity, duration, and frequency.

If I use a cup for my tea that has a glaze in it that is leaching something toxic into the tea, how MUCH is leached into the tea in the time it is in the cup? We can predict some of that based upon results like that is posted in this thread from standardized laboratory testing. That might begin telling us the INTENSITY of the potential exposure.

Next we have to look at the duration of the exposure. For us, the duration is the time we spend drinking the tea and the time it is in our bodies digestive system before being excreted. You body has an amazing ability to deal with many "insults". The shorter the duration of the exposures..... the more time you give your body to do its job and to deal with the problem and recover from it. Iff you drink constantly all day from that same cup mentioned above, that is a different duration than if you have one cup a day.

Closely related to the duration is frequency. Do you drink tea from that cup every day? Every other day? Once a week? Again... time away from the insult gives the body time to deal and heal.

This is very complex. No easy answers except when the issue is so blatant that it IS evident.

For another example, copper is generally not thought to be very toxic if it leaches from a glaze. It affects the taste of foods... but would have to be in really high levels to be worrisome. BUT... if you are the person with the rare Wilson's Disease........ a small amount can kill you.

The issues of the leaching problems is often a bit overblown. The biggest hazards from toxins in the ceramics filed are to the artists... not the consumer. But that is not to downplay the need to be an informed consumer.

Things like governmental water standards can act as guidelines if you know the material your are concerned about and have data to tell you the levels. But remember that those standards are for a certain exposure intensity, duration, and frequency. How does that compare to your consumption of tea?

It depends.

best,

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

[xiaobai]

John,

Thank you so much for your thoughtful and informative posts. I cannot agree more. People often have a very idealized image of Yixing in particular and China in general. Whereas there are still quite a few pristine places there, their numbers are shrinking fast.

In this regard, I really appreciate your efforts to try to educate people. As consumers and tea people, we cannot ignore these facts and we have to demand from artists, farmers, and especially vendors responsibility and transparency. So far, I feel there are too many grey areas in the tea trade, despite the leaf having been with us for millenia and, in the Chinese culture, being considered as one of the seven basic necessities (http://en.wikipedia.org/wiki/Seven_necessities).

Best!

Xiao Bai