Lead testing yixing pots


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Postby britt » Sep 7th, '08, 08:59

I think this is great, but we should all keep in mind the fact that lead contamination is only one of many issues. I don't know if there's any way to test for other substances, such as industrial dyes, chemicals, etc. IMO those are just as important as lead.
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Postby britt » Sep 13th, '08, 18:38

Another forum member (I think it was Mary R) posted this link on another thread but I can't find it. It is also relevant here.

Stephane Erler of Tea Masters found lead in Yixings to be negative.

From "Keep the tea pleasure pure"

"I think we can put this concern about lead to a complete rest for most tea ware. Most earth ware (like Yixing pots) and porcelain are fired at temperatures above 1200 degrees Celsius to succeed."

http://teamasters.blogspot.com/search?q=Yixing+lead

However, Stephane did not come up negative on other issues like chemicals and dyes mixed with the clay.

From "Zhuni clay is extinct!"

2. Buyers beware

"This means that over 90% of modern zhuni teapots currently on the market are fake. Such teapots are made with a mix of red clay, zisha clay and/or other hard stones. Some unscrupulous business people even add chemicals to the clay. This practice, unfortunately, is not limited to the copying of zhuni but of any kind of yixing teapot."

http://teamasters.blogspot.com/search?q=Zhuni+clay+is+extinct%21+
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Postby Woots » Nov 11th, '08, 11:18

I am new to the tea enthusiast world and I began looking for some Yixing pots for my starting collection of tools and came across this thread. (I have long suspected these clays may have heavy metals in them as well, which is why I found this thread)

I started doing research on lead inspection kits.
-Which are the best and give most accurate results?
-Whats the best method to test pottery for accurate results?

What I came up with is the following and I thought I would share my findings.

I found a report done by consumer reports saying that a brand called "Lead Inspector" was their favorite. Click Here For Link
Its 13 dollars and has 8 tests. They mention that brands like First Alert give false negatives (which is bad).

I also found a website that gives procedures on how to do all kinds of lead tests accurately. Click Here For Link
Here is a snippet off that site that directly applies to all of us testing Yixing (testing pottery)

SPECIAL TEST PROCEDURE (Patented Leach Method)

Use this procedure to quantify the approximate lead release in pottery/ceramic ware, multi-layered paint or paint chips, mini-blinds, toys, children's jewelry, Mexican candies, make up and candle wicks. You can test almost anything with this method.

* Wash, rinse and dry the item you wish to test
* Fill the item with white vinegar (or immerse the item/sample in vinegar). Allow to stand for a minimum 4 hours.
* Test resulting vinegar with Indicator Solution supplied in the kit.
* Compare color produced to the chart supplied with the kit.


I thought that since Yixing retains flavor and that's very important to us and getting rid of the odor of vinegar will take a lot of time I am considering doing this test to the lid portion of the Yixing pot only (since it comes into the least contact with the tea) it should still contain the same clays used as the main pot as well as the same surface glazes or pigments on the outer shell (if any are used at all). The other reason I like this vinegar method is you Yixing doesn't have to come in direct contact with the chemicals used in the test kits.

I know this thread is a couple of months old, but I hope I am contributing something useful to the community here. I plan on buying a few nicer Yixing pots over the next month or so. I will perform the tests and let everyone know my findings.
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Postby edkrueger » Nov 11th, '08, 11:35

You should just test the bottom of the pot.
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Postby gingkoseto » Nov 11th, '08, 11:52

britt wrote:I think this is great, but we should all keep in mind the fact that lead contamination is only one of many issues. I don't know if there's any way to test for other substances, such as industrial dyes, chemicals, etc. IMO those are just as important as lead.


Exactly! I can imagine many bad manufacturers wouldn't use lead, which is almost murdering. But I can imagine some (or even many of them) use other unpleasant chemicals or dyes. Current zi sha market is very disordered and nurtured a lot of bad products.

I also learned that some manufacturer mix "glass materials" (silicon?) in "yixing" pot (hum, quite creative:lol: ). Which is not a health concern but then the product is not worth a price of "yixing".
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Postby eanglin » Nov 11th, '08, 14:57

edkrueger wrote:You should just test the bottom of the pot.


I used to work in the Quality Assurance testing lab in Kmart International Headquarters in Troy MI. (No longer exists. Kmart is a fragment of the company it once was.)

I did lead testing as part of the testing process for Childrens clothing. We tested buttons, snaps, zippers and anything else that was painted. Our sister lab tested anything that wasn't associated with clothing.

Testing the bottom of a pot with one of these contact tests will only show lead if there are large enough amounts of lead that the tiny amount of acid tin the kit can leach some out in the brief time you are rubbing the test area. Thais is a HUGE amount of lead that is readily releasable. Lower quantities of lead and lead firmly bound up in less soluble substrates is likely to go undetected

The legal test for determining lead content in paint requires removal of a sample of the paint using mechanical friction or chemical solvents. This permanently damages the painted surface.

The test for China dinnerware and other food grade items involves putting an acid solution into the object, allowing it to soak for a predetermined time, and then testing the acid solution for lead. In the lab I worked in we used a infrared spectrophotometer to determine the precise quantity of lead released into the acid solution or contained in the paint sample.

Such preciseness isn't required for home testing of antiques, but unless you are leach testing, the results you are getting from home testing kits aren't likely to mean a thing- the amount of time the chemical has to react with the substrate is probably insufficient to leach enough lead to get a strong color reaction unless truly huge amounts of lead are present.

Personally, I'm pretty comfortable using Yixing clay pots. I'm not comfortable using antique glazed and painted pots and cups. The CPSC website has many warnings on it regarding fancy painted Chinese porcelain, but I've seen none regarding any yixing-esque earthenware pots.

If anyone wants the ASTM test numbers for the methods we used I can look them up, but I'm sorry, I don't know them off the top of my head.
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Postby beachape » Apr 26th, '09, 13:44

Hello,

I know this thread is kind of old, but has anyone tried testing their yixing by soaking part in vinegar and then using one of those kits?

I am waiting for my cheap pot to come in the mail and I want to test it before I use it. I ordered some of those Homax test swabs for 5 bucks.

Does anyone know how sensitive the tests are? They say that they can detect lead in porcelain, but is the lead content of porcelain glaze much greater than the amount of lead that I might find in an unglazed yixing? Let me know what you think.
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Re: Lead testing yixing pots

Postby yinwenqian » Jun 1st, '11, 22:47

there is no lead in yixing clay teapot
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Re: Lead testing yixing pots

Postby ChinesePottery » Jun 2nd, '11, 00:01

That there is no lead in Yixing pots in general is a rather bold claim as it's obviously being tested for good reason. But I take it, its just lost in translation a little and no lead is supposed to be in any Yixing teapots.

I wrote here http://www.teachat.com/viewtopic.php?f=36&t=15208&p=190255&hilit=+test#p190255 a while back about compulsory testing for owners of shops in the official Yixing ceramics city market. If you buy from artists there (also online) they will happily provide you with a copy of the latest test.
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Re:

Postby JBaymore » Jun 11th, '11, 23:15

eanglin wrote:
edkrueger wrote:You should just test the bottom of the pot.
The test for China dinnerware and other food grade items involves putting an acid solution into the object, allowing it to soak for a predetermined time, and then testing the acid solution for lead. In the lab I worked in we used a infrared spectrophotometer to determine the precise quantity of lead released into the acid solution or contained in the paint sample.

Such preciseness isn't required for home testing of antiques, but unless you are leach testing, the results you are getting from home testing kits aren't likely to mean a thing- the amount of time the chemical has to react with the substrate is probably insufficient to leach enough lead to get a strong color reaction unless truly huge amounts of lead are present.


Dead on!

A piece passing a home test kit type test is no assurance that it will meet current US FSDA lead leaching release standards. A piece FAILING a home test kit is GUARANTEED to fail standardized leach testing.

So the investment of the money in the home kits only is useful in detecting a gross fail.

As many of you who have been here a long time know, SOMEWHERER in the forum threads a long while ago when this subject came up (as it does all the time) I posted a link for a lab that does standardized leach testing for about $30-50 a pop (per metal). This is one of the labs that I recommend to my ceramic materials chemistry students.

But remember you need to send an actual piece to be tested. And that it is minimally destructive...... meaning that the leachate will affect the interior surface for any materials that can be disolved out.

Clay bodies are not usual subjects for the addition of lead compounds. Lead is a POWERFUL flux on silica at all temperature ranges. So any addition of lead would make the firing of such a clay body a bit "touchy", since the forumlation would need to be quite exact. A tiny bit off and the body would be under-fluxed or badly melted. Kinda' crazy for the potter to make the body harder to work with. There are other solutions to tighten a body , if needed.

The usual "suspect" for lead is work with glazes. In Asian ceramics, the place to look for it is particulary in pieces using overglaze enamels (called Aka-e in Japanese ceramics....... literally "red picture"). Mainly seen on porcelains but also a bit on stonewares.

At the higher stoneware and porcelain temperatures (1200-1300 C).....lead is pretty volatile. Even if it was included in the glaze formulation, most of it would have boiled out of the melt before the glaze set on the cooling cycle. High temp firing is no guarantee..... but it lessens the likelihood of an issue.

As to OTHER potentially toxic substances....... that is for sure also of concern.

best,

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