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Results of Yixing lead/cadmium leach test with SGS

by xiaobai » Feb 10th 15 4:19 am

After thinking hard about it and worrying perhaps too much (partly due to the rumors often discussed on TeaChat and other Forums), I decided to go ahead and test some of my Yixing pots with S.G.S. Taiwan.

Indeed, some times people talk too much about lead and cadmium leaching out of Yixing clayware, but I wonder how many tea-chatters have actually taken the action of testing their pots.

Anyway, after finding that it is not so expensive to commercially conduct such tests, I decided to go ahead and submit five samples for testing with the well-known company S.G.S., which is present in many countries besides Taiwan.

I will be uploading copies of the reports in the following days. However, for the moment, let me provide you with some background info about the samples:

Four of the five pots are modern Yixing (that is, made in recent years). From my personal collection, I chose three relatively expensive hand-made pots, which I use a lot. Two of them from well known vendors: Essence of Tea and White2tea. These two are relatively high-end pots (> 200 USD).

The other modern pot is a hand-made one that I obtained from one of my teachers here in Taiwan. Very nice aged Zini hand made pot and also not particularly cheap (~ 100 USD). Finally, there is a very cheap (<30 USD) Yixing "laoduanni" pot that I bought from a local vendor.

The final member of the sample set is 90s Yixing pot, which I got from another teacher of mine for which I paid about 70 USD.

More on the results and further details soon. Stay tuned!
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Re: Results of lead/cadmium leach test of Yixing with S.G.S.

by wert » Feb 10th 15 4:50 am

I am interested to hear more but I wouldn't be surprised by the findings, similar studies had been done before.

Also, with yixing prices, US$200 is quite a way from high end. I think at that price point, it is firmly in the commercial retail category.

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Re: Results of lead/cadmium leach test of Yixing with S.G.S.

by xiaobai » Feb 10th 15 5:04 am

wert wrote: Also, with yixing prices, US$200 is quite a way from high end. I think at that price point, it is firmly in the commercial retail category.
Of course, what I mean by 'high-end' is relative. Obviously, not those famous master artistic pots that are so expensive that one would not dare to ever use them. The pots that I tested are utilitarian not decorative, and include some very cheap stuff that can be found on the internet for <100 USD (in Taiwan for less than 30) and some second-hand stuff that can be found in Taiwanese antique shops.

The range of clays is also relatively diverse. Some of it is aged clay, in some cases possibly coming from Factory 1 sources. Other clays are modern Yixing, which, as described by Aaron Fisher (aka "Wu De") in the last Global Tea Hut issue is coming most likely from places like Anhui, after the mines in Huanglongshan were closed in 2005, and being mixed with all kinds of "junk" as can be seen in many internet videos.

None of the pots that I tested are made of red (hongni-like) clay, however.

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Re: Results of lead/cadmium leach test of Yixing with S.G.S.

by xiaobai » Feb 10th 15 9:25 am

Ok, here are some snapshots from the first SGS report. This is for a qing duanni pot made by artist Fan Jiangfeng (not the famous Fan Jiangfeng who mostly makes artistic teapots though).

Purchased from White2tea and used for sheng puerh so far. Results of the test for Lead/Cadmium leaching according to the EU protocols: n.d. (not dectected) :D
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Re: Results of lead/cadmium leach test of Yixing with S.G.S.

by xiaobai » Feb 10th 15 11:26 am

Report for an aged Zini pot, which I have mainly used with sheng and roasted Oolongs. The result is the same as above: n.d. :D

Interestingly, this pot gave quite an ambiguous result when I used of those commercial lead test kits available from Amazon. :?
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Re: Results of lead/cadmium leach test of Yixing with S.G.S.

by Drax » Feb 10th 15 12:18 pm

Thanks for sharing, this is very interesting!

I'm curious -- what was the detection limit of the lead testing kit that you used off of Amazon?

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Re: Results of lead/cadmium leach test of Yixing with S.G.S.

by xiaobai » Feb 10th 15 12:27 pm

The last report for today (more tomorrow)... A hei zini pot, from the 1990s.

More pictures of this pot here:

https://plus.google.com/112518490736506 ... 6506049969
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Re: Results of lead/cadmium leach test of Yixing with S.G.S.

by xiaobai » Feb 10th 15 1:01 pm

Drax wrote:Thanks for sharing, this is very interesting!

I'm curious -- what was the detection limit of the lead testing kit that you used off of Amazon?
I used this test kit:

http://www.amazon.com/Watersafe-WS425B- ... e+test+kit

On the leaflet it says that the detection limit is the one set by EPA,
that is, below 15 ppb.

Naively, that should be about a factor 10 lower than the SGS method detection limit (MDL) for lead (0.1 mg/L) , which, now that I realize, may explain why the result was not clear cut (although it seemed to me that it was on the negative side but not clearly...).

However, I am not an expert on this kind of analysis methods, so I do not know if the two procedures can be fairly compared. Maybe someone else can give a more informed opinion.

[And, by the way, the kit does not tell you about the Cadmium leaching, which is far more dangerous... :mrgreen: ]

Anyway, thanks for bringing up this point!

UPDATE: It seems the MDL for lead (Pb) of the Inductively coupled plasma atomic emission spectrometer (ICP-AES used by SGS) depends on the wavelength of the Pb line detected by the spectrometer. See:

https://books.google.com.tw/books?id=D9 ... ES&f=false
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Re: Results of lead/cadmium leach test of Yixing with S.G.S.

by Drax » Feb 10th 15 1:30 pm

Hrm, if the two separate systems are correctly calibrated, I don't see why they couldn't be compared. It would be helpful to know what conditions typically cause false positives and false negatives, just to have a sense.

For example, the lab is likely running a calibration before it does its actual measurement. Such a calibration run was probably not possible with the testing kit. I think in this case, you're left with relative certainty that the lead content is under 100 ppb, but uncertainty at the 15 ppb level.... not satisfying, I know.

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Re: Results of lead/cadmium leach test of Yixing with S.G.S.

by xiaobai » Feb 10th 15 1:46 pm

Drax wrote:Hrm, if the two separate systems are correctly calibrated, I don't see why they couldn't be compared. It would be helpful to know what conditions typically cause false positives and false negatives, just to have a sense.

For example, the lab is likely running a calibration before it does its actual measurement. Such a calibration run was probably not possible with the testing kit. I think in this case, you're left with relative certainty that the lead content is under 100 ppb, but uncertainty at the 15 ppb level.... not satisfying, I know.
I am going tomorrow to SGS to collect my pots, so I will ask them for further details about the calibration and the MDL.

However, for this particular pot, the worst case scenario is that the lead leaching is slightly below the level of 100 ppb = 0.1 mg/L (but above 0.01mg/L). If I was to drink from this pot alone, I would need to drink more than 20 L of tea a week in order to reach the maximum limit set by the EU for a person with my body weight. That's more than 20 gongfu sessions a week or three session per day...

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Re: Results of lead/cadmium leach test of Yixing with S.G.S.

by Chip » Feb 11th 15 12:47 am

Hello xiaobai, I have moved your topic to a location where it will be more at home. For the time being I have left a shadow in the original location, I will remove this shadow in a few days. Your friendly moderator, Chip

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Re: Results of lead/cadmium leach test of Yixing with S.G.S.

by xiaobai » Feb 11th 15 12:49 am

Chip wrote:Hello xiaobai, I have moved your topic to a location where it will be more at home. For the time being I have left a shadow in the original location, I will remove this shadow in a few days. Your friendly moderator, Chip
Thank you, Chip! :D

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Re: Results of lead/cadmium leach test of Yixing with S.G.S.

by Chip » Feb 11th 15 12:53 am

Anytime! :mrgreen:

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Re: Results of lead/cadmium leach test of Yixing with S.G.S.

by ryancha » Feb 11th 15 5:09 am

Thanks for posting all of this. Fascinating.

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Re: Results of lead/cadmium leach test of Yixing with S.G.S.

by xiaobai » Feb 11th 15 9:53 am

And... here is the cheapo (~30 USD) bought from a reliable
tea merchant in Maokong, near Taipei.

Test result for Lead/Cadmium leaching: Nope! :D

This is a bit striking because there are quite a lot of rumors that
pots in this price range may be toxic, etc.

Yet, this pot is made of a nice clay (certainly, not from "legendary" sources, but nice) and it brews a wonderful (Muzha) Tie Guan Yin.

The craftsmanship is also excellent, the clay is smooth, relatively high fired (for such a porous clay as duanni), pours very fast, and the pairing was rather obvious and I was never under the impression that I had to break the teapot brewing the same tea for a long time.

In a nutshell, a jewel :mrgreen:
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