ACTSNYC@cs.com on mon 17 apr 00
> ---------- Forwarded message ----------
> Date: Sun, 16 Apr 2000 18:11:53 EDT
> From: Peter Atwood
> Reply-To: Ceramic Arts Discussion List
> To: CLAYART@LSV.UKY.EDU
> Subject: Leaches!
> Resent-Subject: Leaches!
> ----------------------------Original message----------------------------
> Hi All,
> Sometimes I think we potters get a little carried away with this issue of
> food safety. As John Hesselberth pointed out in a recent posting, the
amount
> of copper actually leached
> from a glaze he was testing was very small when exposed to a normal
> concentration of acid. That is, the usual leaching test done in the lab was
> far more severe than what the glaze would be exposed in actual life. Also,
> the duration of exposure is generally far less than the duration of the lab
> test. <
The leach tests are meant to leach more than you would be normally exposed to
so that a considerable safety factor can be built into the standard.
The FDA must build into their standards all kinds of things such as how often
people will use their ceramic ware, what percentage of what they eat or drink
will be in contact with it, and how long food and drink will be in contact
with the surface (e.g., see the different standards for plates, cups, and
decanters).
That's what is so difficult for me to explain here on Clayart. There is a
lot of background material for each standard, and most of this background is
not simple. And changes are being made all the time. For example, all EPA's
pesticide standards used to be based on the exposure of an adult eating a
"normal diet" (which has changed over the years). Now EPA has to look at
children, and vegetarians, people with special health problems, etc., etc.
I try to bring some of that to the glaze problem by using the water
standards, but I know that we really need to get FDA to set standards for
other metals. In the process of setting standards we will all learn a great
deal. The reason is that the regulatory process requires FDA's scientists to
develop all the technical information and draw on all the current data bases
to write up their rationale for setting their limits. This material is then
published in the Federal Register as a "proposed rule" which is open to
public comment. Usually 99% of the comments come from industry because they
have the money to put their scientists on the job of trying to get FDA to set
less protective standards. A few comments usually come from consumer
advocates (sometimes including me) .
Then FDA's scientists must answer the comments and defend their proposed
standards or agree with comments and change the standards and put them out
for comment again. Then when FDA finally decides on what the standards
should be, they publish a "final rule." At this time, you can be certain
that various industries will take FDA to court and try to lower the standards
that way. And in this way, the process is reviewed once again.
This is the way the regulatory world works. And, although very slow, I can't
think of a better way to do it. But simple, it ain't.
>
> I don't know if barium would follow the model above but I suspect it might.
> That might be another direction for the lab testers to follow if they ever
> get the chance.
>
> That brings me to another stupid question: If a glaze is tested and found
to
> leach x number of mg/l of a compound isn't it unlikely that the glaze will
> continue to leach the exact same amount upon subsequent occasions? After
> all, there is less and less metal available after each leaching. So it
would
> follow that there would be diminishing returns. <
Now that is an interesting question. The work that Dr. Sheets published on
this problem with old lead glazes showed that if you leached repeatedly
within a short period of time, the glaze leached less with each test.
However, if you put the piece away for a few months and then tested again, it
leached what the first test found!
The only time a glaze might ever stop leaching is if the toxic metal is just
a thin layer at the surface which can be removed. This might be true of
"fumed" pieces. But then, when they stopped leaching, they'd also stop being
iridescent.
Toxic metals in glazes do not come to the surface and jump into food.
Instead, it is the whole glaze that is dissolving--albeit that some metals
dissolve a little faster than others. For example, the aluminum data I have
is primarily from lead glazes. Clearly, at the same time that lead is
leaching, so is aluminum and every other metal in the glaze.
>
> As far as the aluminum controversy is concerned I think it is total RUBBISH
> and I think anyone who would cause potters to worry about such nonsense
> should have a heart. Potting is a tough enough way to make a living without
> needlessly scaring them.
> Peter Atwood
>
And thank you, too.
Monona Rossol
ACTS
1818 Thompson St., # 23
NYC NY 10012-2586 212/777-0062
ACTSNYC@cs.com
| |
|
