Martha Muzychka on thu 6 feb 97
Dear People,
I have received a request from a potter (formerly from canada) now in
China who has questions about lead. He wants to make his workshop, craft
space lead free. The workshop is presently making earthenware tiles and
bowls for people to work on and also stoneware items for sale. He uses a
gas kiln.
When they set up, the Chinese consultant provided them with something
called on-glaze (which I have undertood to be underglazes). he has become
aware of the problems with lead but would like to know what to use
instead.
He knows about the Clayart Glaze Base (and I have tried to search the
ClayArt Archive) but are there commercial underglazes he can use at
earthenware temps which won't be too costly to ship to Beijing or are
there ones he can make himself?
Also sometime ago I read that there were places in Canada which would test
pots for food safety. My hard drive crashed last fall, and although I had
saved most on backup, there were some thigns I lost -- like that list.
Could any Canadians whoi might have that info email me?
Thanks so much.
Martha
__________________________________
Calvin: I've been thinking, Hobbes.
Hobbes: On a weekend?
Calvin: Well, it wasn't on purpose.
mailto:muzychka@plato.ucs.mun.ca
Marianne Lombardo on sat 6 apr 02
I would like to know if there is a way to tell if a pot that would be =
used for food/drink has lead in the glaze. Other than lab testing.
Looking at a glaze on something I bought a year ago, and reading some of =
the glaze recipes in Chappell's book the effect is like a description in =
that book, with a glaze containing lead bisilicate.
Marianne Lombardo
Omemee, Ontario, Canada
Paul Lewing on sat 6 apr 02
on 4/6/02 7:35 AM, Marianne Lombardo at mlombardo@NEXICOM.NET wrote:
> I would like to know if there is a way to tell if a pot that would be =
> used for food/drink has lead in the glaze. Other than lab testing.
There are commercially available test kits for testing for the presence of
lead. You can generally get them at hardware or paint stores, and many
ceramic suppliers carry them. Also, my old copy of "Glazes for the Craft
Potter" by Harry Fraser details a test for lead using chemicals readily
available at a drugstore. I assume the same test is in his new edition.
Paul Lewing, Seattle
Snail Scott on sat 6 apr 02
At 10:35 AM 4/6/02 -0500, you wrote:
>I would like to know if there is a way to tell if a pot that would be used
for food/drink has lead in the glaze. Other than lab testing.
You can get test kits at the hardware store.
-Snail
John Hesselberth on sat 6 apr 02
on 4/6/02 10:35 AM, Marianne Lombardo at mlombardo@NEXICOM.NET wrote:
> I would like to know if there is a way to tell if a pot that would be used for
> food/drink has lead in the glaze. Other than lab testing.
>
> Looking at a glaze on something I bought a year ago, and reading some of the
> glaze recipes in Chappell's book the effect is like a description in that
> book, with a glaze containing lead bisilicate.
>
> Marianne Lombardo
> Omemee, Ontario, Canada
Hi Marianne,
Almost every hardware store sells lead testing kits. They can be used to
test for lead in painted surfaces or lead in ceramic glazes. They cost
about $10 for enough to test 3 or 4 things.
John
Web sites: http://www.masteringglazes.com and http://www.frogpondpottery.com
Email: john@frogpondpottery.com
"The life so short, the craft so long to learn." Chaucer's translation of
Hippocrates, 5th cent. B.C.
Jenny Lewis on wed 21 may 03
Hi May and everyone,
I have just recently been rummaging through the archives for some
information on lead glazes, because the evening class I go to has a
selection of lead-infested colours for earthenware. Only one of the
buckets is marked "NOT for food use", the rest of them are supposed to
be ok. However, I get the impression from the reading I have done, that
lead migrates and can affect other stuff that is in the same or
subsequent firings. Have I got this right, and should I be avoiding
earthenware at class, for this reason at least?
Also, somewhere in the archive messages someone mentioned that using
bisilicate, sesquisilicate, whatevers, won't make any difference during
the firing, as it doesn't know it has been fritted and in the kiln it
melts and is just plain old lead.
I prefer stoneware anyway, and use it most of the time. Just thought a
bit of terracotta would be nice for a change. But I think I should
avoid it at this particular venue.
Jenny Lewis
London UK
(May - where in London are you?)
Ron Roy on thu 22 may 03
Hi Jenny,
If lead glazes are fired in a kiln the lead does move around - especially
if there is not a strictly oxidizing atmosphere. This can happen in
electric kilns - the fumes from a bisque firing can be carried in the
bricks over to the next firing for instance.
It is not right that using fritted lead will make gazes stable - in the end
the stability of the glaze will depend on how much alumina and silica is
present - how much copper (and other colouring oxides) is in the glaze and
if it is well melted.
I would be interested to know what criteria are being used to verify which
glazes are durable. I have the sinking feeling it is some ones opinion but
based on what.
I agree - trying to make stable functional ware at low fire temperatures is
very difficult unless you know what you are doing - and then you have the
open, water absorbing clay to deal with. Stoneware temperatures are so much
better for functional ware.
RR
>I have just recently been rummaging through the archives for some
>information on lead glazes, because the evening class I go to has a
>selection of lead-infested colours for earthenware. Only one of the
>buckets is marked "NOT for food use", the rest of them are supposed to
>be ok. However, I get the impression from the reading I have done, that
>lead migrates and can affect other stuff that is in the same or
>subsequent firings. Have I got this right, and should I be avoiding
>earthenware at class, for this reason at least?
>
>Also, somewhere in the archive messages someone mentioned that using
>bisilicate, sesquisilicate, whatevers, won't make any difference during
>the firing, as it doesn't know it has been fritted and in the kiln it
>melts and is just plain old lead.
>
>I prefer stoneware anyway, and use it most of the time. Just thought a
>bit of terracotta would be nice for a change. But I think I should
>avoid it at this particular venue.
>
>Jenny Lewis
>London UK
>(May - where in London are you?)
>
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Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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