Lou Raye Nichol on wed 11 nov 09
Hello,
I have returned to potting after 20 years gap. I am concerned about lining
vessels for food with copper glazes. This was not regarded as an issue when
I left. Does lining a pot with a copper carbinate glaze carry health
hazards?
Lou Raye Nichol
John Hesselberth on thu 12 nov 09
On Nov 11, 2009, at 10:40 PM, Lou Raye Nichol wrote:
> Hello,
>
> I have returned to potting after 20 years gap. I am concerned about
> lining
> vessels for food with copper glazes. This was not regarded as an
> issue when
> I left. Does lining a pot with a copper carbinate glaze carry health
> hazards?
>
> Lou Raye Nichol
Hi Lou,
It is not necessarily a matter of safety except for the small percent
of the population who have Wilson's disease (they can't eliminate
copper from their system like most can). To me it is more a matter of
craftsmanship and durability of your work.
Copper is the most difficult colorant to keep in a glaze. Glazes that
are properly formulated can hold 4-5% with minimal leaching, but many
glazes you will find in the literature and some commercial glazes are
not that well formulated. Copper can also make food taste bitter at
concentrations as low as 5 ppm. Poorly formulated copper-containing
glazes will visibly fade with use. The acids in food or the bases in
dishwasher detergent will leach the color right out of them.
If you plan to use copper as a colorant on functional work, at the
very least vinegar test it. My personal choice is not to use copper on
food bearing surfaces, but I will use it on the outside of functional
work in a properly formulated glaze.
Regards,
John
William & Susan Schran User on thu 12 nov 09
On 11/11/09 10:40 PM, "Lou Raye Nichol" >
wrote:
> I have returned to potting after 20 years gap. I am concerned about linin=
g
> vessels for food with copper glazes. This was not regarded as an issue wh=
en
> I left. Does lining a pot with a copper carbinate glaze carry health
> hazards?
Copper is an issue in pottery glazes when used as a liner that may come int=
o
contact with acidic liquids/food.
We all need copper in our diet, but too much additional copper can be
harmful, so we as potters need to be aware of potential hazards in the
functional pottery we sell to the public.
20 years ago it was simple ignorance of the facts by many potters and
teachers. It's been the research and publications of folks like John & Ron
that have provided us the information about making & firing functional and
stable glazes that won't leach harmful elements. Also the research,
publication and dissemination by folks like Monona about health & safety
handling the materials we use.
Copper is one of the more difficult materials to keep locked into a glaze.
One needs to know how to mix and fire a stable glaze that supplies
sufficient silica to form good glass. One also needs to know limits on adde=
d
colorants to create glazes that will prevent them from leaching form the
glaze.
I would suggest you carefully read Mastering Cone 6 Glazes before you embar=
k
on your return to pottery.
Here's the site to learn more:
If you contact John or Ron, you could probably get them to sign the book!
Bill
--
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
Snail Scott on thu 12 nov 09
On Nov 12, 2009, at 7:35 AM, John Hesselberth wrote:
> Copper is the most difficult colorant to keep in a glaze... The acids
> in food or the bases in
> dishwasher detergent will leach the color right out of them...
I don't do much with copper glazes, and not on
foodware, but I had a green-glazed mug by a
prominent local potter which I used mainly for
soft drinks, and always handwashed (don't own
a dishwasher). I'd had it about two years, using
it perhaps twice a week, when I broke it. That's
when I noticed the glaze had gone completely
brown on the inside. Not staining, but leaching.
I mentioned it to the maker next time a saw her.
She was shocked when she saw the shards; she'd
had no idea that the glaze could leach like that.
No harm, no foul, but I suspect most of us seldom
see what our work looks like after long use.
-Snail
| |
|
