Stephanie Wright on fri 5 jan 07
Hi Everybody!
Is there a way to formulate a copper red glaze (^10R) that would be
considered safe to use on dinnerware? The information I have gathered so
far says no, and that a liner glaze would at least need to be used on the
inner portion of the vessel. However, I recently saw some dishes online
where the inside of the dish was what the potter claimed was copper red.
It certainly looked the correct color. So, what's the deal?
And thank you to everyone on the list who has been so kind and helpful!
Stephanie
Stephanie Wright on sat 6 jan 07
Thanks to all of you who answered! I can't tell you how much better I feel
about this now.
FYI, nobody on the listserv implied that copper red could not be used on
functional ware. However, I did pick the info up in some of
my "independent study" along the way. It may be that what I read was
outdated material. I'll have to check through my notes, etc.
What I would specifically like to try out are these two red glazes:
June Perry=92s Raspberry Copper Red
Custer Feldspar 57.87
Whiting 8.76
Dolomite 3.71
Ferro Frit 3134 4.94
Ferro Frit 3195 3.37
Silica 21.35
Copper Carbonate 1
Tin Oxide 1
Red Iron Oxide 1
Tom Coleman=92s Copper Red
Kingman Feldspar 40
Silica 80
Nepheline Syenite 40
Soda Ash 30
Whiting 36
Tin Oxide 4
Bentonite 2
Copper Carbonite 1
If anyone is already using them, I would love to hear any comments on how
you like them! :-)
Stephanie
Ron Roy on sat 6 jan 07
Hi Stephanie,
I see no reason why not. All you need is a durable glaze - send any you
want to test and I'll probably be able to tell you if it's durable.
Easy to send a sample to a lab and see if it's acceptable for a liner glaze.
RR
>Hi Everybody!
>
>Is there a way to formulate a copper red glaze (^10R) that would be
>considered safe to use on dinnerware? The information I have gathered so
>far says no, and that a liner glaze would at least need to be used on the
>inner portion of the vessel. However, I recently saw some dishes online
>where the inside of the dish was what the potter claimed was copper red.
>It certainly looked the correct color. So, what's the deal?
>
>And thank you to everyone on the list who has been so kind and helpful!
>
>Stephanie
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Vince Pitelka on sat 6 jan 07
Stephanie wrote:
> Is there a way to formulate a copper red glaze (^10R) that would be
> considered safe to use on dinnerware? The information I have gathered so
> far says no, and that a liner glaze would at least need to be used on the
> inner portion of the vessel. However, I recently saw some dishes online
> where the inside of the dish was what the potter claimed was copper red.
> It certainly looked the correct color. So, what's the deal?
Stephanie -
I don't think that you have anything to worry about with glossy copper red
glazes on food contact surfaces. I am curious as to where you have gathered
this information. Most cone 10 copper red glazes contain less than 1%
copper, and the color appears when the copper aggregates in colloidal
suspension in the glaze melt, and the chances of copper leaching into food
are so small that I cannot imagine any danger at all. The primary problem
with copper leaching is in glazes containing higher percentages of copper,
especially matt glazes or those where some copper oxide precipitates out on
the surface of the glaze. Has anyone else on this list implied that
high-fire copper red glazes should not be used on food contact surfaces?
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
Dan Semler on sat 6 jan 07
Hi Stephanie,
I had Jeff's Red (a cone 10 copper red) leach tested once, for both copper
and barium - it contains both. The lab found 0.091mg/L of copper and 0.056
mg/L of barium leaching out. Not a whole lot of either. This could be
compared with a cone 10 oribe I had tested at the same time which leached
20.6 mg/L.
Jeff's Red has about 0.5% copper carb in it. The Oribe I tested had about
5% I think.
HTH
Daniel
Lee Love on sun 7 jan 07
Remember, the original scare about copper was in lead glazes,
where it allowed lead to leach into food/drink.
--
Lee in Mashiko, Japan
Minneapolis, Minnesota USA
http://potters.blogspot.com/
"Let the beauty we love be what we do." - Rumi
"When we all do better. We ALL do better." -Paul Wellstone
Ron Roy on sun 7 jan 07
Hi Vince,
Sounds like you are saying that you can tell by the look of a glaze if it
is stable and durable - I know you don't mean that but just to emphasize
the point - there are all kinds of unstable glazes around that look just
fine.
I agree that most copper reds I have seen are perfectly acceptable as liner
glazes - but I also suspect there are some that are unstable and will not
wear well.
RR.
>Stephanie -
>I don't think that you have anything to worry about with glossy copper red
>glazes on food contact surfaces. I am curious as to where you have gathered
>this information. Most cone 10 copper red glazes contain less than 1%
>copper, and the color appears when the copper aggregates in colloidal
>suspension in the glaze melt, and the chances of copper leaching into food
>are so small that I cannot imagine any danger at all. The primary problem
>with copper leaching is in glazes containing higher percentages of copper,
>especially matt glazes or those where some copper oxide precipitates out on
>the surface of the glaze. Has anyone else on this list implied that
>high-fire copper red glazes should not be used on food contact surfaces?
>- Vince
>
>Vince Pitelka
>Appalachian Center for Craft, Tennessee Technological University
>Smithville TN 37166, 615/597-6801 x111
>vpitelka@dtccom.net, wpitelka@tntech.edu
>http://iweb.tntech.edu/wpitelka/
>http://www.tntech.edu/craftcenter/
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Ron Roy on sun 7 jan 07
Hi Stephanie,
I would recommend June's over the Coleman glaze - because it looks like a
stable glaze and may not craze on some clay bodies.
The Coleman glaze is loaded with soda - is going to craze on any clay body
and because the alumina is way low - will probably be affected by dish
washing. Subbing G200 for Kingman changes the glaze very little by the way.
RR
>Thanks to all of you who answered! I can't tell you how much better I feel
>about this now.
>
>FYI, nobody on the listserv implied that copper red could not be used on
>functional ware. However, I did pick the info up in some of
>my "independent study" along the way. It may be that what I read was
>outdated material. I'll have to check through my notes, etc.
>
>What I would specifically like to try out are these two red glazes:
>
>June Perry=92s Raspberry Copper Red
>
>Custer Feldspar 57.87
>Whiting 8.76
>Dolomite 3.71
>Ferro Frit 3134 4.94
>Ferro Frit 3195 3.37
>Silica 21.35
>Copper Carbonate 1
>Tin Oxide 1
>Red Iron Oxide 1
>
>
>Tom Coleman=92s Copper Red
>
>Kingman Feldspar 40
>Silica 80
>Nepheline Syenite 40
>Soda Ash 30
>Whiting 36
>Tin Oxide 4
>Bentonite 2
>Copper Carbonite 1
>
>If anyone is already using them, I would love to hear any comments on how
>you like them! :-)
>
>
>Stephanie
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
David Beumee on mon 8 jan 07
I agree with Vince; The copper red recipe I have been using for many years has been professionally tested for copper release, and it proved safe. I'd be happy to share the recipe.
David Beumee
www.davidbeumee.com
Lafayette, CO
-------------- Original message ----------------------
From: Vince Pitelka
> Stephanie wrote:
> > Is there a way to formulate a copper red glaze (^10R) that would be
> > considered safe to use on dinnerware? The information I have gathered so
> > far says no, and that a liner glaze would at least need to be used on the
> > inner portion of the vessel. However, I recently saw some dishes online
> > where the inside of the dish was what the potter claimed was copper red.
> > It certainly looked the correct color. So, what's the deal?
>
> Stephanie -
> I don't think that you have anything to worry about with glossy copper red
> glazes on food contact surfaces. I am curious as to where you have gathered
> this information. Most cone 10 copper red glazes contain less than 1%
> copper, and the color appears when the copper aggregates in colloidal
> suspension in the glaze melt, and the chances of copper leaching into food
> are so small that I cannot imagine any danger at all. The primary problem
> with copper leaching is in glazes containing higher percentages of copper,
> especially matt glazes or those where some copper oxide precipitates out on
> the surface of the glaze. Has anyone else on this list implied that
> high-fire copper red glazes should not be used on food contact surfaces?
> - Vince
>
> Vince Pitelka
> Appalachian Center for Craft, Tennessee Technological University
> Smithville TN 37166, 615/597-6801 x111
> vpitelka@dtccom.net, wpitelka@tntech.edu
> http://iweb.tntech.edu/wpitelka/
> http://www.tntech.edu/craftcenter/
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
Vince Pitelka on mon 8 jan 07
> Sounds like you are saying that you can tell by the look of a glaze if it
> is stable and durable - I know you don't mean that but just to emphasize
> the point - there are all kinds of unstable glazes around that look just
> fine.
Ron -
Oh no, I didn't mean that, and I hope I didn't give that impression. I was
saying that with less than 1% copper in the glaze, it is very unlikely that
there would be any issues with copper release, and I think that would be
true even in a glaze like Coleman's copper red.
> I agree that most copper reds I have seen are perfectly acceptable as
> liner
> glazes - but I also suspect there are some that are unstable and will not
> wear well.
Yes, certainly that is true. In my experience there are so many glazes that
look beautiful and are used and traded widely, but in fact are very unstable
and subject to quick wear. That's probably true of lots of copper reds.
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
Ivor and Olive Lewis on tue 9 jan 07
Dear Friends,
The relationship between Copper and Lead Oxide fluxed glazes will be =
well documented and I would imagine it is described in Parmellee as well =
as in Singer and Singer, Turner and Bull and the other industrial =
references.
But this is an interesting proposition.
I suppose the first step is to use a valid process for measuring the =
degree of leaching of every glaze recipe that is known to contain Copper =
compounds over a variety of concentrations. A costly task ! !.
According to DeBoos, Harrison and Smith (P56), Red Copper glazes are due =
to free copper metal in a "Colloidal" form. They say that when metallic =
copper is first released during the reduction phase the glaze is =
uncoloured then by continue saying that colour develops as atoms of =
Copper aggregate into particles that react with visible light at which =
point the glaze shows colour.
Following from what Vince Pitelka said, that there will always be some =
exposed Copper at the surface of a glaze, a point with which I agree, =
then an acid test will reveal the presence of the element copper, even =
down to parts per billion if the analytical method is good to that =
level.
In order that the element Copper is never, ever, released it has to =
enter into chemical combination with other elements to create a compound =
that is insoluble in water, acidic or alkaline liquids. Can, or has, =
anyone identify and describe such compounds ? ?
I find it to be an interesting fact that the two ceramic melts that =
appear to reject Copper and cause so much concern are those based on =
Lead Dioxide and Silicon Dioxide, two substance that share more than one =
interesting quality ( Lead and Silicon are Group 4a Elements! ! ). Lead =
based glazes and Silicon based glazes seem to share a similar =
relationship with Copper based materials . If the element Lead is =
unstable in the presence of Copper perhaps claims for the instability of =
mid and high temperature glazes would be better understood if Copper =
release was cross correlated with values of Silicon (Si) leaching. That =
would be valuable, radical and revolutionary information.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Ivor and Olive Lewis on wed 10 jan 07
Dear David Beumee,=20
I ask if your statement below means that tests done on your behalf =
registered readings for Copper that were within the limits set by the =
Food and Drug Authorities and that Copper was reported as being present =
in the leachate ?
<years has been professionally tested for copper release, and it proved =
safe. I'd be happy to share the recipe.>>
Been thinking about returning to Copper Reds so, "Yes". I am willing to =
take a short cut and accept a copy of your recipe. Thank you for your =
offer.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
| |
|
