Edmund B Burke on fri 30 jul 99
I have just mixed a very thin cobalt oxide wash and used it over a glaze
on a platter. Do y'all (who know about such things) think it will be
food safe?
Thanks in advance!
Lynne in Atlanta where it is hot, humid and smoggy!
Tetsuya Shimano on mon 2 aug 99
hi edmund!
food test....i'm not sure it's appropriate, but i always use a slice of
orange and put it on the surface of the glaze you wnat to test. just leave
it for 24hours in room temperature. if u see any color changes either on the
galze or on the slice of orange, then the glaze is not good for the food
container. otherwise, if you cannot see any color changes, the glaze is ok.
i have read this test in "ceramics monthly" and i have used this test for the
new glazes which consists of copper oxide, manganese dioxide, and some other
toxic oxides. if anybody has the better test, let me know.
t
John Hesselberth on wed 4 aug 99
Tetsuya Shimano wrote:
>
>food test....i'm not sure it's appropriate, but i always use a slice of
>orange and put it on the surface of the glaze you wnat to test. just leave
>it for 24hours in room temperature. if u see any color changes either on the
>galze or on the slice of orange, then the glaze is not good for the food
>container. otherwise, if you cannot see any color changes, the glaze is ok.
>i have read this test in "ceramics monthly" and i have used this test for the
>new glazes which consists of copper oxide, manganese dioxide, and some other
>toxic oxides. if anybody has the better test, let me know.
Hi Tetsuya,
Unfortunately this orange slice test and an equivalent vinegar test are
only qualitative, not quantitative, and they will only tell you if the
glaze is grossly unstable. To know whether or not a glaze is stable to
leaching you have to have it tested by a professional testing lab.
Fortunately this service is available at a very reasonable cost at the
Alfred Analytical Lab at Alfred University. For complete instructions on
how to do this visit my web site at
http://www.frogpondpottery.com/glazetest.html
Once you have the results you will still have to apply some judgement as
to the allowable level because there are only regulations (in the U.S.)
for lead and cadmium. There is a good discussion of this topic in the
archives with various points of view being represented. In most cases
though, it is possible to make attractive, stable glazes that leach less
metal than is allowable in drinking water. At the very least, I believe
we should aim for levels in the leaching test no higher than 10X the
allowable drinking water level which is about what the lead regulations
require.
Roland Hale of Alfred Analytical and I are generating more data on this
subject and may have better answers in a few months.
John Hesselberth
Frog Pond Pottery
P.O. Box 88
Pocopson, PA 19366 USA
EMail: john@frogpondpottery.com web site: http://www.frogpondpottery.com
"It is time for potters to claim their proper field. Pottery in its pure
form relies neither on sculptural additions nor on pictorial decorations.
but on the counterpoint of form, design, colour, texture and the quality
of the material, all directed to a function." Michael Cardew in "Pioneer
Pottery"
Christine Sawyer on thu 12 aug 99
My understanding is that it is unlikely to be food safe but all so wonder
what other responses you got.
----- Original Message -----
From: Edmund B Burke
To:
Sent: Friday, July 30, 1999 5:41 PM
Subject: Cobalt Oxide Wash
> ----------------------------Original message----------------------------
> I have just mixed a very thin cobalt oxide wash and used it over a glaze
> on a platter. Do y'all (who know about such things) think it will be
> food safe?
>
> Thanks in advance!
>
> Lynne in Atlanta where it is hot, humid and smoggy!
Mary V Smith on fri 13 aug 99
Christine,
It is my understanding that cobalt oxide wash is food safe over a glaze,
and I have used that same technique on bowls. Now you have me wondering
if I am wrong.....Hopefully, someone out there has more info!!!!
Mary
Christine Sawyer wrote:
>
> ----------------------------Original message----------------------------
> My understanding is that it is unlikely to be food safe but all so wonder
> what other responses you got.
> ----- Original Message -----
> From: Edmund B Burke
> To:
> Sent: Friday, July 30, 1999 5:41 PM
> Subject: Cobalt Oxide Wash
>
> > ----------------------------Original message----------------------------
> > I have just mixed a very thin cobalt oxide wash and used it over a glaze
> > on a platter. Do y'all (who know about such things) think it will be
> > food safe?
> >
> > Thanks in advance!
> >
> > Lynne in Atlanta where it is hot, humid and smoggy!
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