Raku Lead Glaze Concern


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Raku Lead Glaze Concern

Postby rhpot1991 » Oct 13th, '08, 11:08

Just wanted to get some opinions on how concerned I should be that raku ware may have used lead glaze. I want to order a raku chawan from artisticnippon.com but after reading this on their site I am a little concerned:

"Stringent Japanese health and safety regulations for tableware recommend that Raku matcha bowls be used solely for drinking tea. This is because the glaze may contain traces of lead which could be released if the bowls are used to serve acidic food. Since matcha tea does not have this effect, Raku matcha bowls are considered safe provided they are used for their original purpose only. "

I really like the idea of ordering something that is hand made and not mass produced, but this is something I will be drinking from every day so the health concern may trump that.
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Re: Raku Lead Glaze Concern

Postby Geekgirl » Oct 13th, '08, 12:46

rhpot1991 wrote:
I really like the idea of ordering something that is hand made and not mass produced, but this is something I will be drinking from every day so the health concern may trump that.


I solved the "drink from every day" problem by buying LOTS of chawans and rotating them. :lol:

:oops:
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Postby chamekke » Oct 13th, '08, 14:21

The reason for the warning is that acidic foods will leach the lead from the raku surface. You do not want to use raku for acidic substances, and you do not want to use raku at all when the drink or food has been sitting in the bowl for some time.

Japanese raku is considered to be safe to drink from when:
- You use the bowl for matcha, which is (a) non-acidic and (b) typically drunk immediately after being whisked.
- You soak the raku bowl in water for a few minutes first (my tea sensei typically allows at least 15 minutes of total immersion!). This way, the crackling and fine interstices of the bowl are completely filled with water, and when you do make the matcha, it won't be soaking into the bowl. (This approach also prevents unsightly staining of the bowl's interior surface.)

I do not use [Japanese] raku under any other circumstances. And I do not use American-style raku for eating or drinking anything, ever. Responsible sellers tell the buyers that American raku is "not for food use", and so they should! I suppose that the latter might be reasonably safe for storing dry foods such as nuts, but I prefer not to take the chance.

On the whole, if you're concerned about using Japanese raku even with the limitations mentioned, it's probably best just to use teabowls made from other methods (Shino, Karatsu, etc.). There's so much choice out there, you really don't have to go the raku route.
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Postby rhpot1991 » Oct 13th, '08, 14:29

chamekke wrote:The reason for the warning is that acidic foods will leach the lead from the raku surface. You do not want to use raku for acidic substances, and you do not want to use raku at all when the drink or food has been sitting in the bowl for some time.

Japanese raku is considered to be safe to drink from when:
- You use the bowl for matcha, which is (a) non-acidic and (b) typically drunk immediately after being whisked.
- You soak the raku bowl in water for a few minutes first (my tea sensei typically allows at least 15 minutes of total immersion!). This way, the crackling and fine interstices of the bowl are completely filled with water, and when you do make the matcha, it won't be soaking into the bowl. (This approach also prevents unsightly staining of the bowl's interior surface.)

I do not use [Japanese] raku under any other circumstances. And I do not use American-style raku for eating or drinking anything, ever. Responsible sellers tell the buyers that American raku is "not for food use", and so they should! I suppose that the latter might be reasonably safe for storing dry foods such as nuts, but I prefer not to take the chance.

On the whole, if you're concerned about using Japanese raku even with the limitations mentioned, it's probably best just to use teabowls made from other methods (Shino, Karatsu, etc.). There's so much choice out there, you really don't have to go the raku route.


The seller did say that it is not for food use:
"* The raku bowls are for matcha tea use only. These bowls can not be used for serving food."

Ideally I would be using this while at work so soaking it is not really an option.
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Postby olivierco » Oct 13th, '08, 14:31

rhpot1991 wrote:
Ideally I would be using this while at work so soaking it is not really an option.


Try a nice kyoyaki bowl. No glaze problems with them.
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Postby rhpot1991 » Oct 13th, '08, 14:35

olivierco wrote:
rhpot1991 wrote:
Ideally I would be using this while at work so soaking it is not really an option.


Try a nice kyoyaki bowl. No glaze problems with them.


Care to point me at some good sites?
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Postby olivierco » Oct 13th, '08, 14:45

I bought some on ebay and some from this nice store

Image
Image
Image

I only own the second one, the other ones are on my wish list!
They sell also less expensive ones:

Image
Image
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Postby Victoria » Oct 13th, '08, 15:57

I found and bought a beautiful Raku tea bowl, that was perfect for tea, but the seller did have the "not for food use". I wrote and said - what is up with that - a Tea Bowl, that is not for food use??? So immediately several very long and involved discussions ensued. So I have quite a bit of knowledge on the subject, some of which has been posted already. The bottom line on my bowl is that after several very long and lengthy discussions the seller coated the bowl with a food safe glaze. I am including the potter's response, there is a lot of reading!

From the potter:
Let me start by saying, I mixed the glazes myself for this piece and they do not contain any lead at all. Then, I believe the "NOT FOOD SAFE" is more of a general health warning as I do know that many people will still use these for tea...however this is what I did find....hope this helps!

>I had always been taught and told that Raku was not only not food safe, but not able to hold water, due to the temperature used in the firings.
>I also remember a post from some time ago from someone talking about the tons of definitely-not-food-safe things in Raku glazes. ...
>...now I'm confused - Raku isn't food safe, can't hold water, but use it as a teacup? What gives? Can anyone give me a quick and simple education in Raku and explain what the differences might be?

Let's take the easy one first - can't hold water. Most raku glazes are
formulated to craze so that upon post-fire reduction, they will acquire a
pleasing crackle pattern. These cracks, small as they are, allow fluids to
seep into the clay body. Depending on the extent of the cracking and the
condition of the clay body, you could see seepage on the outside of the
container in a few minutes, overnight, or maybe not at all. Even if you
don't see seepage on the outside of the pot, enough fluid gets into the clay
that a raku container filled with water should never be placed on a piece of
fine furniture.

Since you typically don't take hours to consume a cup of tea and a small
amount of seepage into the cup doesn't matter, then it is not an issue for
this type of usage. It would be a problem for a vase, but not a tea bowl. If
this concerns you, there are sealers that have been discussed on the list
before. Check the archives.

Now the second issue - not food safe. This is actually two issues. One issue
relates to the microcracking that causes the seepage as described above. I'm
probably going to catch hell from the health care professionals on the list
for this, but I say that for personal items this really isn't an issue. The
argument is that bacteria can get into the cracks along with the fluids and
flourish there. My feeling is that the bacteria that do get into the cracks
are bacteria from our own surroundings. These are bacteria that our bodies
live with all the time. Because we're accustomed to them, they don't make us
sick. It's the same reason that people living in a particular area can drink
the local water all they want and don't get sick whereas if you go visit
them and drink the local water you may very well get sick. If you take a
look at the cups in your house, you'll probably find that at least a few of
them have some evidence of crazing and hence are harboring those same little
bugs.

Let's just say for the sake of argument that I'm wrong, that bacteria in the
cracks of a glaze are dangerous. There is a second thing to consider. Your
body fights off small numbers of dangerous bacteria all the time. You never
even know it. You get sick only when your body receives 1) a large number of
bacteria all at once and can't destroy them quickly enough or 2) the
bacteria are particularly virulent or 3) you are in a particularly weakened
state due to stress of some form (stress can include overwork, temperature
extremes, chemotherapy, ...). The cracks in the bottom of a cup are
relatively hostile places to bacteria - no food or water except for whatever
gets poured into the cup from time to time. Bacteria have a unique defense
to this situation. They form spores or live in a kind of suspended
animation. When a fresh supply of food and water is provided by your pouring
something into the cup, they can come out of their protected state and
multiply. But this takes time. By the time that they can even get into gear
about multiplying, you have finished drinking your tea, washed the cup out
and placed it back in the cupboard. If you receive any bacteria, it is a
small number that your body can easily defeat.

The other issue regarding being food safe has to do with the glaze. Here's
the real problem. Many raku glazes make use of metals that are not good for
you. Besides containing nasties, many raku glazes are not formulated to
produce a good glass that would seal in the metals and prevent them from
leaching into food. A classic copper matte would be an extreme example of
this - almost all copper compound and just enough glass former to hold it
onto the pot.

Raku adds one more complication that is very difficult to overcome. In most
other forms of glazed pottery, you can usually find a formulation that
either eliminates dangerous materials or else immobilizes them somehow,
usually by trapping them in the glass matrix. Once you think that you have a
good glaze, you can send it off for testing to determine if you have any
leaching above acceptable limits. As long as you maintain your recipe and
firing you should be OK with that glaze. The very nature of raku firing
makes it impossible to assume that a glaze produced in one firing will act
like the same glaze in a different firing. The atmosphere in the kiln is
often very uneven. The length of time that pieces are allowed soak at the
glaze melting point often varies. Lord only knows what kinds of variables
are introduced by the post-fire reduction.

So the only thing that you can do to ensure a food safe raku glaze is to
formulate the glaze with materials that are not dangerous to begin with or
are otherwise stable in themselves so that they do not rely on the glass to
prevent leaching.
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Postby Space Samurai » Oct 13th, '08, 16:06

I have a few raku from Artistic Nippon and I'm not dead yet.
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Postby chamekke » Oct 13th, '08, 16:19

rhpot1991 wrote:
chamekke wrote:And I do not use American-style raku for eating or drinking anything, ever. Responsible sellers tell the buyers that American raku is "not for food use", and so they should! I suppose that the latter might be reasonably safe for storing dry foods such as nuts, but I prefer not to take the chance.


The seller did say that it is not for food use:
"* The raku bowls are for matcha tea use only. These bowls can not be used for serving food."


Just for clarification - in the quote above, I was referring mainly to sellers of American raku. Most will forewarn you that their American raku is not for food use, but some are not as explicit as they should be.

Toru-san of Artistic Nippon is selling Japanese raku. He is impeccably honest, and I would certainly expect him to let his customers know the conditions under which they should use their teabowls. However, the only Japanese raku I have ever seen that was made for "food or drink" is the chawan or teabowl. All other Japanese rakuware I've seen is used for non-food purposes, e.g. incense containers. Therefore, many sellers of Japanese raku chawan (especially sellers of secondhand Japanese teawares) will assume that the person drinking from it already KNOWS not to use it for anything other than matcha, and may not think to include instructions on its use.

Incidentally, the Facts page on the Tea Toys site discusses this at some length. It's worth a read. The author does mention that there are mukouzuke dishes made of raku for tea kaiseki, so it's not true that there are no other dishes used for food and drink. Still, the same conditions apply.
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Postby t4texas » Oct 13th, '08, 19:45

chamekke wrote:The reason for the warning is that acidic foods will leach the lead from the raku surface. You do not want to use raku for acidic substances, and you do not want to use raku at all when the drink or food has been sitting in the bowl for some time.

Japanese raku is considered to be safe to drink from when:
- You use the bowl for matcha, which is (a) non-acidic and (b) typically drunk immediately after being whisked.
- You soak the raku bowl in water for a few minutes first (my tea sensei typically allows at least 15 minutes of total immersion!). This way, the crackling and fine interstices of the bowl are completely filled with water, and when you do make the matcha, it won't be soaking into the bowl. (This approach also prevents unsightly staining of the bowl's interior surface.)

I do not use [Japanese] raku under any other circumstances. And I do not use American-style raku for eating or drinking anything, ever. Responsible sellers tell the buyers that American raku is "not for food use", and so they should! I suppose that the latter might be reasonably safe for storing dry foods such as nuts, but I prefer not to take the chance.

On the whole, if you're concerned about using Japanese raku even with the limitations mentioned, it's probably best just to use teabowls made from other methods (Shino, Karatsu, etc.). There's so much choice out there, you really don't have to go the raku route.


Maybe I've missed something, but why not use American-style raku for matcha? How is it different from Japanese raku?
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Postby beecrofter » Oct 13th, '08, 19:51

Test swabs to check for lead content are stocked in Ace Hardware stores in the USA and also ship via their website. This link is one of the products-
http://www.acehardware.com/product/inde ... 8141047234
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Postby rhpot1991 » Oct 13th, '08, 20:06

beecrofter wrote:Test swabs to check for lead content are stocked in Ace Hardware stores in the USA and also ship via their website. This link is one of the products-
http://www.acehardware.com/product/inde ... 8141047234


I have used some of these in the past (not the same brand but I'm fairly sure they are all the same). Unfortunately they can leave behind a permanent orange stain. I'd kinda like to figure out what to do before I spend a good portion on a chawan instead of testing it later and being sad about wasting the money.
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Postby chamekke » Oct 13th, '08, 20:15

t4texas wrote:Maybe I've missed something, but why not use American-style raku for matcha? How is it different from Japanese raku?


Well, that's a good question. I've been looking at different websites and trying to puzzle that out. Supposedly American raku does not typically use the lead glaze found in Japanese raku... so you would think it would be safe, in terms of lead content at least. A typical ingredient in those beautiful iridescent glazes is copper, judging from the glaze recipes I've seen on the Web.

On the other hand - almost all the sellers of American raku I've encountered are super-careful to mark their wares as "ornamental only - do not use for food" (or similar).

I do know that American raku glazes can contain a lot of different ingredients, and perhaps it's some of the non-lead ones that are problematic.

In short: I don't know! Perhaps there's a potter (or pottery-savvy person) on this forum who can shed more light?
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Postby brandon » Oct 13th, '08, 20:27

I have heard from many people that American made raku is less safe.

"Western raku potters rarely use lead as a glaze ingredient, due to its serious level of toxicity. Japanese potters substitute a non-lead frit[1]. Although almost any low-fire glaze can be used, potters often use specially formulated glaze recipes that "crackle" or craze (present a cracked appearance), because the crazing lines take on a dark color from the carbon."

[1] A frit (sometimes spelled fritt) is a ground glass or glaze used in pottery. Some materials have to be fritted before they can be used because they are soluble or toxic. For example, some lead compounds are toxic, and borax, used in glaze as a flux and a glass former, is soluble. The modern potter uses lead as a frit of lead bisilicate (PbO.2SiO2), lead sesquisilicate (2PbO.3SiO2) or lead monosilicate (PbO.SiO2). Borax will be used as a frit of sodium diborate (Na2.2B2O3.10H2O) or anhydrous borax (Na2.2B2O3).

All text from respective Wikipedia articles.
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