Cherie Jemsek on wed 15 oct 03
We have been using Copper Carbonate or Copper Oxide in a Barium Matt glaze
for 6 years now. In the last year we have had consistent problems with
fuming...big problems...like contaminating everything else in the kiln
including the shelves & furniture. Having already gone through the obvious
possibilities, we have decided that the Copper itself is the culprit. The
color of the raw material definitely changed at the beginning of the year.
We have slowly adapted to our use of it but the limitations caused by the
fuming onto our yellow glaze has produced a very muddy palette. Venting has
helped but the proportion of venting required is ridiculous.
Has anyone else had similar problems?
Steve & Cherie
Earl Krueger on thu 16 oct 03
On Wed, Oct 15, 2003, Cherie Jemsek wrote:
> We have been using Copper Carbonate or
> Copper Oxide ... In the last year we have had
> consistent problems with fuming...
> contaminating everything else in the kiln
> The color of the raw material definitely
> changed at the beginning of the year.
(Caveat: I'm not an expert on glazing and
firing but I do understand a little about
heavy metals.)
I'm not normally an alarmist but this sounds
pretty scary to me !!!!
If you're sure it's the copper materials I would be
worried that it might be contaminated with some
other heavy metal like lead or arsenic or mercury
or such that evaporates off at your firing
temperature.
You are going to have to make some decisions.
Just because you can "control" it, somewhat, by
venting may not mean that what you produce
is safe for you or your customers (students?).
If you are satisfied that you can "control" it by
venting, where are the fumes going?
Spending a little money for some testing may
either give you a lot of peace of mind or evidence
to take to your supplier (or lawyer, if the need arises).
In the mean time I would suggest you discontinue
use of these materials and obtain good supplies
from a known reputable supplier. If the problem
then goes away I would either return the faulty
stuff or if its not that big an investment just discard it.
If you do discover what exactly is at fault it would be
good information to share with the Clayart community.
Anxiously waiting to hear more on this.
Earl...
Bothell, WA
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