raku chawan food safe ?


Discussion on virtually any teaware related item.

Talk about casting a blind eye!

Postby Intuit » Jun 19th, '09, 15:43

Every single web page I reviewed that were posted by potters making and selling raku plainly state: "Not Food Safe, Not Waterproof!" Most also added the warning, "for decorative use only".

Soaking the vessel overnight in hot water is absolutely worthless for leaching heavy metals from glazes and clays and rendering your raku tea vessel 'safe to use'.

The point here isn't that the metals will leach under mildly acidic conditions (they will, but the rate depends on the glaze and pottery matrix chemistry, erosiveness and porosity; metal speciation, tea infusion strength and pH, tea type, infusion and vessel wall temperature and contact time), because most Japanese and American raku potters are said to use lead-free frit/glazes.

The warning is that the material surface is not impervious to liquid penetration and vessel wall mineral efflux. The material is macroporous and it's not fired at high enough temps to make it inert. It can harbor bacteria, molds/fungi and viruses, especially in the vessel bottom where residue may sit after decanting, and when present in concentrated pastes during the early stages of mixing (matcha) and at the rim from oral contact. These vessels can leach loosely bound mineral constituents and contaminated food residues into the infusion broth.

Some raku vessel interiors are coated with a sealant to improve water retention when the pot is to be used under wet conditions (to hold plants, soaps, etc.

They are still not food safe, even if they feature an interior sealant layer.

Use at your own risk.

Depending on the clay used, the pottery can bind and retain water when the glaze doesn't act as a surface sealant. That's why frequent use (and soaking) of Hagi tends to afford low-leakage conditions, although the vessel may 'sweat' (form a condensate film on the outside from liquid passing through the wall).

For matcha, you may want to consider pouring it off immediately after preparation into a safe drinking cup, and washing the residual out of the raku or hagi vessel promptly.

Matcha isn't neutral, but weakly acidic, as is fresh green tea. Oolong is intermediate in pH range of teas and pu'erh and black teas are the most acidic. Still, the most acid teas are much weaker than coffee and many herbal tissanes (which may be even more acidic and erosive to tooth enamel than orange juice, surprisingly enough).
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Re: Talk about casting a blind eye!

Postby MarshalN » Jun 19th, '09, 18:58

Intuit wrote:Every single web page I reviewed that were posted by potters making and selling raku plainly state: "Not Food Safe, Not Waterproof!" Most also added the warning, "for decorative use only".


There's a simple reason why they say this -- it's a disclaimer that allows them to say "I said it's not foodsafe, don't sue me" or "I said it might leak, don't ask for your money back". We buy Hagi ware knowing full well they will leak. We buy (and use!) them anyway.

Intuit wrote:The warning is that the material surface is not impervious to liquid penetration and vessel wall mineral efflux. The material is macroporous and it's not fired at high enough temps to make it inert. It can harbor bacteria, molds/fungi and viruses, especially in the vessel bottom where residue may sit after decanting, and when present in concentrated pastes during the early stages of mixing (matcha) and at the rim from oral contact. These vessels can leach loosely bound mineral constituents and contaminated food residues into the infusion broth.


Whatever it might have in the clay, I'm pretty sure virus is not one of them. Also, there is a reason why you're supposed to dry out the piece thoroughly after use.

The whole debate is silly. Instead of worrying about whatever imaginary minerals that might be leeching into the tea or what not, it's probably better to worry about what's in the water to start off with, what sort of pan you use to cook, what you might be eating when you are going out, etc. A trace amount of copper (or even lead) in your tea from the very occasional use of a matcha bowl is probably the least of your problems.
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Re: Talk about casting a blind eye!

Postby sriracha » Jun 19th, '09, 19:08

MarshalN wrote:or even lead


I vaguely remember reading about tea having about 4x the amount of lead compared to water.

Which had me worried for a minute or two. :D

Seriously though, is there any truth behind this?
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Re: Talk about casting a blind eye!

Postby MarshalN » Jun 19th, '09, 19:18

sriracha wrote:
MarshalN wrote:or even lead


I vaguely remember reading about tea having about 4x the amount of lead compared to water.

Which had me worried for a minute or two. :D

Seriously though, is there any truth behind this?


Do you mean infused tea, of any kind, prepared in any vessel, has four times the amount of lead than water?

What water are you talking about? A lead-laden one, or a lead-free one? What's our reference?

That sounds like a strange claim.
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Postby sriracha » Jun 19th, '09, 19:27

I guess it referred to an average. Any tea, tap water.

I'm sorry I can't remember the details but it's been ten years or more since I read it.
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Postby entropyembrace » Jun 19th, '09, 20:46

My guess is that the tea shrub will absorb lead in the soil and concentrate in in the leaves...irc most plants do that with minerals in the soil, it's why green vegetables are so full of things like calcium.

Also I've found that not all teas are acidic, I was suspicious of that claim given the flavour profiles of many teas I drink so having a couple of those pH test strips that health food stores like to hand out to make you scared of your blood being slightly acidic (by telling you to test your urine LOL) laying around I used them to test an infusion of Ying De Gold which had what I figured had an alkaline flavour profile...and sure enough the test result showed it to be slightly alkaline...around 7.5 pH.
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Postby Seeker » Jun 19th, '09, 21:22

:o
Cool discourse.
Geez, with all this scary talk, it's like - take the pag down, oh no, put it back on the shelf, take it down, put it back up a la Saturday Night Fever.
I just can't decide. Might as well dance! :)
But, ... I remain calm, though my arm is getting numb.
I thought about using it this morning, but ultimately decided against it.
I'll follow my own spirit, my own qi, and one of these days it'll probably find its way into the rotation-- or who knows, maybe not. :?
Meanwhile, the shelf is in very good air circulation, so it'll be dry.
Also, I can run it through my Tersano Sanitation System before any use - produces ozonated water-- highly valent oxygen in that state kills viruses and bacteria and molds/mildews, microorganisms etc - also grabs onto other stuff (remember - many municipalities use this system on a grand scale to purify city drinking-water supplies).
Also - pag DOESN'T warn against using his bowls, and he uses them every day.
All so very interesting.
:P
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Postby xuancheng » Jun 19th, '09, 21:22

entropyembrace wrote:...I used them to test an infusion of Ying De Gold which had what I figured had an alkaline flavour profile...and sure enough the test result showed it to be slightly alkaline...around 7.5 pH.


I was always under the impression that tea plants liked a fairly alkaline soil and growing conditions.

seeker wrote:Also - pag DOESN'T warn against using his bowls, and he uses them every day.
All so very interesting.


See if you can get some of his blood and test it for lead. Since he uses his own bowls every day, if lead levels in his blood are accceptable, you can set your mind at ease.
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Postby Seeker » Jun 19th, '09, 23:19

xuancheng wrote:See if you can get some of his blood and test it for lead. Since he uses his own bowls every day, if lead levels in his blood are accceptable, you can set your mind at ease.

As I mentioned earlier in the topic (you may not have read that far back), he doesn't use lead of any kind in either glazes or clay body. He also doesn't use any kind of barium or manganese. There are copper, cobalt, and tin though.
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Postby MarshalN » Jun 19th, '09, 23:26

xuancheng wrote:
See if you can get some of his blood and test it for lead. Since he uses his own bowls every day, if lead levels in his blood are accceptable, you can set your mind at ease.


The fearmongers will tell you that the lead gets deposited in the fat tissues and other places, so you won't find it in the blood :)
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Huh?

Postby Intuit » Jun 20th, '09, 12:17

The standard lab test for lead exposure in humans is a blood test.
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Postby Moss » Jun 20th, '09, 15:15

Copper and lead do leach. Lead is worse, but copper is bad. Barium will also leach and is bad. Manganese, cadmium, vanadium and uranium will leach (uranium is not a common ingredient in glazes in the US btw. I reckon leached uranium would be a bad thing...)

Aluminum will not leach and it is in every single piece of pottery ever made, just part of the process so wouldn't worry on that.

Iron leaches some, but it is actually good for you so again, don't worry.

The argument over bacteria is old and I think mainly an American problem. Something like the banning of import of raw milk cheese. If one person in 100 million got even a tummy ache, I'd give you a dollar. Also bacteria will need protein to grow and I think that tea is pretty low on that.

American Raku and Japanese Raku both, leave porous bodies so if you leave your tea in them for hours, they will probably go through to whatever is under the cup.

I use raku that I make. I never use barium, copper, lead, manganese or the others on the inside although I might on the outside lip where there is no continuous contact with the liquid so no leaching. Inside I only use iron or glass forming chemistry (silica, calcium, sodium, aluminum. iron, etc.) I don't use raku from anyone else unless I ask them specifically what is in the glaze. I also never use raku for anything but clear liquids like tea.

Clues that your raku cup might have bad metallic oxides are that it is metallic, especially bronze or copper colored (manganese). Bright colors that look like an oil slick (copper). Bright reds or yellows (lead and cadmium). Shiny glazes are less likely to leach than matte glazes. Lead is EASY to test for, you can get home test strips that cost about $3 each and are 100% reliable.

I think that not using some of these pieces is a shame, but you really have to know what is in the glaze.
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Postby Moss » Jun 20th, '09, 15:28

Lead does not collect in the fat regardless of what your fear mongers say. It collects 95% in the bones and 5% in blood where it is passed out extremely slowly through urine. If you have been exposed, you will find it in blood tests.

Cobalt interestingly, is not very harmful. It was added to all beer from about 1900-1940 to help keep the head on the pour. It was reported that cobalt toxicity became a problem for people drinking 2+ liters daily for a period of years. You might imagine that they also had other issues at that point.

Acids and bases (alkali) are both corrosive and can cause problems with soft glazes so that is not a good indicator.

I agree with MarshalN The debate is silly in comparison with pesticides on vegtables or simply living downwind of an industrial area.
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Postby Seeker » Jun 20th, '09, 15:44

Hey Moss,
I have one of your chawan from Teance! I'll share the pic soon - love it! One of my faves!
Regarding copper and my pagasari chawan and leaching (I'll assume tin isn't an issue since you didn't mention it).
I have stopped using it for now, but I miss it and am trying to determine if I will use it again.
I would only use it for matcha, which I typically drink over the course of 10-20min.
That certainly isn't hours. Also, I always warm my bowls with boiling or near boiling water and then dry them right before sifting matcha in. Will there likely be leaching in 10-20 or even 30 min?
Thanks!
Peace!
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Postby Moss » Jun 20th, '09, 15:59

Hey Seeker! Thank you! Teance called yesterday and they want more so hopefully that will be a relationship that grows with time.

There were 6 there, and a couple were really really nice. It was a darned good firing, glad you like them.

OK copper is a problem if it is in concentrations over 5% in a stable glaze which raku technically is not in that it has not formed a real glass where everything is (mostly) bound up.

I am not a chemist to tell you if it is OK or not to use unfortunately.

Personally I would not be *that* worried because we all have copper water pipes and we get food cooked (if we're lucky!!!) in copper. If you are concerned you can get the piece tested and that might not be a bad thing. I don't know the cost. Here is a good list of labs. http://digitalfire.com/services/database.php?list=labs

Leaching is a chemical process of ions being pulled out of the glaze matrix by acids or bases. It has nothing to do with the heat or the water used or how dry it is so washing it or not won't make a difference.

Oribe glaze has high levels of copper as well I might add, but people use that all the time. Most green glazes in fact are copper based. In high fire wares, it is much less of a problem.
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