Brenda Z on tue 19 dec 00
John,
I was very surprised to see cadmium on your list, right up there with lead.
I was unaware that cadmium was so toxic.
I have been buying commercial glazes and underglazes for any pottery that I
intended to use for food, since I have very little knowledge of glaze
materials. I recently bought a commercial underglaze that contains cadmium.
The label states that it is dinnerware safe (if used under a specific clear
glaze), and the bottle is clearly marked as NONTOXIC. The only warning on
the label is that the underglaze should not be sprayed. Now I am wondering
if I can trust the labels on the commercial glazes that I am buying.
I let my kids paint with this underglaze (at least the pieces where
sculptural). Now I am wondering about what kinds of risks I have exposed
the kids to.
I am also thinking about throwing out the bottle of underglaze. I would
rather err on the side of safety, and put purple flowers on my pots
instead of red ones.
Brenda Z.
http://www.members.home.net/brendaz
-----Original Message-----
From: John Hesselberth
To: CLAYART@LSV.CERAMICS.ORG
Date: Tuesday, December 19, 2000 2:53 PM
Subject: Re: toxicity issues
>Here are the things I am personally very careful of and/or don't
>personally use. They all can be used safely with proper precautions, and
>I use most of them.
>
>Lead in any form (I don't personally use)
>Cadmium in any form (I don't personally use)
>Manganese dust and fumes
>Dusts which might contain free silica (very definitely including clay
>dust)
>Barium carbonate (don't ingest; also I don't use it in functional glazes)
>Chromium containing dusts/powders
>Nickel containing dusts/powders
>Dioxin containing materials (??? I just don't know enough to comment. I
>don't think anyone else does at this point either)
>
>I'm sure others will add a few other materials that I have overlooked
>above
>
John Hesselberth on wed 20 dec 00
Brenda Z wrote:
>I was very surprised to see cadmium on your list, right up there with lead.
>I was unaware that cadmium was so toxic.
>
>I have been buying commercial glazes and underglazes for any pottery that I
>intended to use for food, since I have very little knowledge of glaze
>materials. I recently bought a commercial underglaze that contains cadmium.
>The label states that it is dinnerware safe (if used under a specific clear
>glaze), and the bottle is clearly marked as NONTOXIC. The only warning on
>the label is that the underglaze should not be sprayed. Now I am wondering
>if I can trust the labels on the commercial glazes that I am buying.
Hi Brenda,
Cadmium is one of the two materials (lead being the other) regulated by
the FDA for use in ceramics. It is regulated in most of the rest of the
world too. If you use cadmium YOU are responsible for assuring that the
leaching is below the specified levels. The FDA doesn't tell you how to
do this, they just tell you what the limits are and place the
responsibility clearly in your hands. The limits on cadmium are even
lower than they are for lead. To quote from Sax "Dangerous Properties of
Industrial Material": "The oral toxicity of Cd compounds is HIGH.
However when these materials are ingested, the irritation and emetic
action is so violent that little of the Cd is absorbed and fatal
poisoning does not as a rule ensue...." Sax goes on to describe in great
detail the body responses to various types of exposure to cadmium. They
aren't pleasant.
I think if you will carefully read the material that comes with your
glazes you will find an extremely thorough disclaimer statement which
says, essentially, "we believe these glazes are safe when applied and
fired according to instructions, but if they are not it is YOUR problem,
not ours" In other words, the manufacturers accept no liability; you are
on your own if there is a problem.
How careful are the manufacturers? I know some are pretty careful. I
have also found commercial glazes that say they are "food safe" yet are
so bad I can draw the color right out of them with the vinegar test or by
simply laying a juicy slice of lemon on the glazed surface for as little
as an hour. Indeed, maybe all that material that leaches out won't kill
anybody, but glazes that perform as I described above are certainly not
suitable for functional work. You will see some examples of glazes like
these if you are able to attend my NCECA presentation in March.
Bottom line: You must test things yourself! I would certainly not place
my safety or the safety of my customers in the hands of a glaze
manufacturer knowing what I know about at least one of those
manufacturers. There are apparently no well defined standards in the
industry, or if there are, no policing mechanism. There are some
excellent glazes out there; there are also some that are just pure
garbage!
Regards, John
"The life so short, the craft so long to learn." Hippocrates, 5th cent.
B.C.
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