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cadmium toxicity for firing/application (fwd)

updated sat 23 dec 00


ACTSNYC@CS.COM on thu 21 dec 00

> ---------- Forwarded message ----------
> Date: Wed, 20 Dec 2000 23:48:43 -0500
> From: Mitsuru Cope
> Reply-To: Ceramic Arts Discussion List
> Subject: Re: cadmium toxicity for firing/application
> Please tell me how dangerous for application and firing underglaze which
> contains cadmium? Does cadmium absorb through skin? <

No one knows if it skin absorbs. People assume it doesn't, but I have never
seen a single test. Remember, they said the same thing about lead, and now
we know it does skin absorb.

But even if it does, my assumption is that this would be a very minor route
of exposure. I would worry more about not washing your hands really well
after application, dragging home a little dust every day from the shop to the
house, or inhaling kiln emissions. These and other scenarios end up putting
cadmium in your environment where you have months or years of low level

> I saw a Don Reitz's beautiful tea bowl on Ceramics Monthly ad. He used
> velvet underglaze 383 and wood fired it at cone 11. It looked fabulous, so
> ordered it without knowing the contents. <

If the underglaze is showing a red or yellow color it is still there. This
is obvious. If it all burned off it would disappear.

How much did that bowl cost?

> My local ceramic supplier told me that cadmium melts around cone 01,
> therefore, there is no danger of cadmium if I fire at cone 5. <

Unfortunately, he's wrong.

There are no hard and fast rules about when cadmium or lead burn off. It
depends on how thick the overglaze, the composition of the over glaze, and
more. It would be nice if we could look at the melting point of metals such
as lead and cadmium, and infer that all their complexes and compounds melt at
this temperature as well It just isn't so.

And the melting point is the temperature at which a metal beings to
fume--that is goes into the air in an oxide particle form. But the process
only begins there. It increases in speed with temperature. And it may never
be completely gone--some metal in some form will remain behind.

Chemicals do not suddenly convert from one form to the other. It is more
like ice. At 33 o F the ice is suddenly not all gone. It begins to melt
then, but will take time before it is all water. And some of the water will
turn to vapor at this phase, but only a little. As the temperature
increases, more ice melts and more water vapor is released. But if the
temperature drops again (when the firing is over and the kiln is turned off)
the ice that didn't melt will remain.

I hope this helps.

Monona Rossol
181 Thompson St., #23
NYC NY 10012-2586 212/777-0062
Mitsuru Cope