raku chawan food safe ?


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Postby Chip » Jun 20th, '09, 19:57

Very informative, and I am glad to have a very diverse group of participants giving a wide range of views. :idea: :!: :arrow:

Regarding higher temps, Moss, doesn't higher temp speed these reactions?
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Postby Moss » Jun 20th, '09, 20:01

Higher temps may effect them to some degree on thinking about it, but I don't think it would be that much. The temp is not going to be the big factor compared to the time and the ph.
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Re: raku chawan food safe ?

Postby GreenwoodStudio » Jan 8th, '10, 13:42

This is a topic that potters go around and around with. Moss makes some really good points, and I think that the answer is that it depends.

Oxides leaching out of the glaze would be my main concern. I've seen teabowls for sale that horrify me to think someone would actually be using them. Shiny copper or rainbow type glazes, BAD! In fact I would probably go as far to say that any colored raku glaze is not good (with the possible exception of iron being used as the colorant).

Now white glazes, clear crackles and such, I would worry about much less. However I would still want to know what was in the glaze. Glazes composed mainly of frit I would consider pretty safe. Tin used in small amounts to make the glaze an opaque white would be fine in my book (tin is used to line whisky flasks because of its resistance to acidity) The main thing would be for the glaze to be a fairly stable glass.

Another thing that might concern me would be the materials used for the post-firing reduction. Often folks use newspaper which has all kinds of nasty stuff in the inks used. These chemicals when burned have the potential to be absorbed into the clay, and later leach out. If natural materials like leaves, pine needles, or sawdust (from untreated wood) are used in the post-firing reduction I would consider that fine.

As far as the clay being absorbent with the potential to grow bacteria, well I guess that depends as well. What are you going to put in it? Raw sushi, would probably be very bad. Tea, not so much. If that were the case any teaware made of Yixing clay should immediately be thrown away!! Actually all clay (with the possible exception of a VERY vitrified porcelain) is still absorbent after it's been fired to 'maturity'. It's just a matter of degree. So, if you have any pottery that has a glaze that's crackled or crazed, the potential to harbor bacteria is present.

Man, I could go on forever, so this is my 2 cents for now. Buy your raku wares from someone who's knowledgeable about the safety of the materials used in their process and enjoy it!!
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Re: raku chawan food safe ?

Postby Seeker » Jan 9th, '10, 01:24

G - thanks for the post.
Enjoyed the read quite a lot.
My pagasari chawan has copper, so I rarely use it; and I always soak/warm first. And when I do use it - ONLY matcha.
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Re: raku chawan food safe ?

Postby Serg » Jan 9th, '10, 04:05

I really understand your concern about health. But now I am quiet confused. I used to think that we actually need some minerals for health! I have here some multi vitamin/mineral tabs and they contain metal oxides and salts in amounts of mgs. And these metals are Cu, Mg, Mn, Fe, Sn, Zn, Cr and some more. And we are supposed to intake one tab a day. So what do you think?
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Re: raku chawan food safe ?

Postby GreenwoodStudio » Jan 9th, '10, 13:42

Serg-

I would not stop taking your vitamins. Your right we all need the things in our bodies to a degree. Your vitamins are supplying you with a controlled dosage and specific form of these metals and such, while an unstable glaze is not. I have a really pretty copper glaze that I use on non-functional work that when I rub it a bit, I can see copper being tranfered to my finger and it even smells metallic. Yuck, not the way you want to ingest these things.
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Re: raku chawan food safe ?

Postby Serg » Jan 9th, '10, 14:30

Yes, I really don't want to eat metals :) So Copper is bad... hmm... magokorodo at ebay has some beautiful kazuwa ware which is said to be copper glazed. I like it a lot and I was thinking about buying some. So is kazuwa ware food safe?
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Re: raku chawan food safe ?

Postby GreenwoodStudio » Jan 9th, '10, 14:49

Serg wrote:Yes, I really don't want to eat metals :) So Copper is bad... hmm... magokorodo at ebay has some beautiful kazuwa ware which is said to be copper glazed. I like it a lot and I was thinking about buying some. So is kazuwa ware food safe?


magokorodo's work is beautiful, it's also not Raku. Totally different. Copper in a stable glaze is perfectly fine. I loves me some copper reds and oribe :) By all means buy one and enjoy it.
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