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leaching (fwd)

updated wed 26 apr 00


Monona Rossol on sun 29 nov 98

---------- Forwarded message ----------
Date: Fri, 27 Nov 1998 15:25:59 EST
From: John Fazzino
Subject: Re: leaching
---------------------------Original message----------------------------
> Hi, I'm at Providence College and we've been having our science dept run
> some tests on barium leaching in cone ten glazes. Apparently they use an
> acidic substance in the pot and then test that.<

Please see if they are running ASTM C 738 (aka AOAC 973.32) so the data they
get will relate to the FDA's and Alfred's leach data.

> He said that he ran the
> tests several times and each time got a lower reading, less barium. His
> thought was that, leaving this substance,(we could use vinegar), in the pot
> would leach the toxins out and it would be safe. Although inconclusive,
> (he's running another set of tests), it would seem that this is plausible.<
> John Fazzino <

Barium does not migrate to the surface of a rock hard glaze and them jump
out into the acid. The only way a substance can leach for a while and then
stop is if the source of the substance is a fine layer on the surface. This
can happen if the metal is fumed on the surface in the kiln.

Usually, leaching indicates that the whole glaze--and every ingredient
in it--is dissolving slowly in the acid. If you test for other metals in the
glaze, you will find them, too.

But leaching is time-dependant. So if the amount of barium in the leachate
seems to be reducing, leach the hell out of it until it appears to stop
leaching. Then let the pot sit for a while--weeks, months--and give
it another test. It is likely that it will be leaching again. But if it is
not, then and only then I would believe that the substance was just on the
surface and is now gone.

Monona Rossol
Arts, Crafts and Theater Safety
181 Thompson St., # 23
New York NY 10012-2586 212/777-0062

Monona Rossol on thu 15 apr 99

---------- Forwarded message ----------
Date: Wed, 14 Apr 1999 10:41:48 EDT
From: Dorothy Weber
Subject: Re: leaching
----------------------------Original message----------------------------
Here is another question to all of you knowledgeable folks. We have recently
started using an oribe glaze, that produces some very interesting results. We
fire to cone 10 reduction. If used on a bowl it produces a translucent green
glaze, turn metallic where thin and where thick will have red/cranberry
areas, on lidded vessel the interior will turn cranberry red. we did a leach
test with the vinegar in both. The cup/bowl did change to a lighter shade
(left a line) after 3 days. Interesting it was still clear when poured into a
glass. Then the lidded vessel after one week never altered the interior.
What's happening? Can anyone tell me about these chemicals/changes? I welcome
any info

custer feldspar 80
whiting 20
bentonite 2
copper carbonate 5

Thanks! Dorothy
Manakin-Sabot, Va.

It's probably leaching copper and you are using a rather large amount of
vinegar. This means that the blue/green copper acetate is too dilute to
detect visually.

And the fact that you can't see a color change in the other should give you
no great comfort. Many glazes that show no change are still leaching
excessive amounts.

You really should have the leach test done professionally if you use or sell
these for use with food.

Monona Rossol
181 Thompson St., #23
NYC NY 10012-2586 212/777-0062 on tue 25 apr 00

> ---------- Forwarded message ----------
> Date: Sun, 23 Apr 2000 20:17:39 EDT
> From: John Baymore
> Reply-To: Ceramic Arts Discussion List
> Subject: Leaching
> Resent-Subject: Leaching
> ----------------------------Original message----------------------------
> The reason that any of us with any scientific literacy at all look
> dubiously upon your "research" is due to such comments as this:
> >Can anyone out there help me? There have been a number of orange juice
> >incidents, but I seem to remember that one happened in the 1970s or 1980s
> in Canada. I can't find my file on this and would appreciate anyone who
> couldpoint me to a record of this incident. As near as I can remember, a
> >kept orange juice in a jug in the frig. I don't think it was Mexican
> ware.
> >When her twin boys came down with symptoms of the flu which were actually
> >lead poisoning symptoms she doubled up on the orange juice to get more
> fluids
> >into them. I think one twin died or was brain damaged.
> This is NOT data, it is a story--a not a very believeable one the way you
> have told it. "I seem to remember....", "I can't find my file on this..."
> "As near as I remember...." "I don't think it was Mexican ware..."
> (meaning you don't know), "I think one twin died..."
> You obviously don't really know what you are talking about.
> Interesting response...........
> I took Monona's post not as a scare story, but as Monona honestly
> requesting some HELP from those of us on CLAYART in locating some more data
> in order to continue her research as to the validity of the concerns being
> expressed by many about leaching issues. Yes...... it IS a STORY
> ................. that is being relayed in order to narrow down the search
> to a specific incident about which someone might have real hard FACTS.
> Being a scientific semi-literate person , I take Monona's information
> the same way I take anyone's. She has academic credentials in both
> ceramics and industrial hygiene. For what she currently does with respect
> to health hazards in the ceramics field, that is a reasonable background to
> say that she at least "has a clue". Does she know absolutely everything?
> No. But no one does. We must not expect perfection from anyone.
> And the old addage about not shooting the messanger is a good one to
> remember.
> respectfully,
> .............................john
> John Baymore
> River Bend Pottery
> 22 Riverbend Way
> Wilton, NH 03086 USA

Thank you John. I couldn't believe that post. But I guess I should.
I have put one of my researchers on it. I need to know if the story is true
or not, where it came from, etc. I remember reading it in an article of
some sort but never checked it out. That's all I was trying to do.

I have always offered help whenever I can give it, but you can be sure I'll
never ask the forum in general for help again.