Kim Hohlmayer on tue 1 jul 08
Hi All,
Even after 20 years working in clay and teaching it there is still a lot I don't know. Here is my question. I have worked in four public art centers as well as my own studio. In two out of the four public ones there were glaze/body fit problems that led to crazing. I was told and read that this usually leads to leaching out of glaze ingredients into food stored or cooked in said pots. Not only were students not told about this but the glaze ingredients were not available so one could figure out what exactly might be leaching into ones casserole of coffee.
Needless to say, I warned all my students and anyone else who would listen. However, to the best of my knowledge, the one center has never done anything about this in spite of my remarks. The other place is fixing the issue even as I type.
Am I just a paranoid alarmist? Shouldn't the one center limit the use of clay bodies and glazes to ones that fit each other for students making ware for food use?
In other centers where commercially produced glazes are use can we take the label as it is printed that the glazes are safe when fired according to directions? I am guessing that the answer will be "Test! Test! Test!" but want to hear from all sides. I hope some of the commercial glaze makers are reading this because I would like to hear from them too. Thanks. --Kim H.
Lee Love on wed 2 jul 08
On Wed, Jul 2, 2008 at 5:06 PM, Vince Pitelka wrote:
> containing copper, chrome, manganese, or barium is crazing, I would only use
> it on non-food-contact surfaces.
Copper is not in the same category as these other oxides. It really
was a good idea when we switched from lead pipes to copper ones. I
believe the plastic ones are a health risk. The original copper
scares have been when copper is associated with a lead glaze. The
copper allows the lead to leach more easily.
The lack of copper in our foods (leached out of the soil because
of the use of fertilizers and pesticides) is possibly related to Mad
Cows and Alzheimers. I also wonder if the switching from copper
plumbing to plastic is having an effect too.
My experiment with the pennies in the birdbath is still working
well. Some algae grows in the bird bath, but not as much as in the
past.
--
Lee Love in Minneapolis
http://mashikopots.blogspot.com/
http://claycraft.blogspot.com/
"We are such stuff as dreams are made on, and our little life is
rounded with a sleep." --PROSPERO Tempest Shakespeare
Vince Pitelka on wed 2 jul 08
Kim Hohlmayer wrote:
"Even after 20 years working in clay and teaching it there is still a lot I
don't know. Here is my question. I have worked in four public art centers
as well as my own studio. In two out of the four public ones there were
glaze/body fit problems that led to crazing. I was told and read that this
usually leads to leaching out of glaze ingredients into food stored or
cooked in said pots."
Kim -
Crazing in itself is not a hygiene problem. There is no evidence that
anyone has ever been sickened due to bacteria in craze cracks. It seems
that it simply does not happen, even with low-fire ware.
We use things like copper, chrome, manganese, and barium in glazes, and if
these glazes are used on food-contact surfaces then of course we must ensure
that the glazes are stable and without flaws. Crazing could be a pathway
for possibly toxic materials to leach out of the glaze, and thus if a glaze
containing copper, chrome, manganese, or barium is crazing, I would only use
it on non-food-contact surfaces.
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka@dtccom.net; wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka
Ron Roy on sat 5 jul 08
Hi Kim,
It would be better to have liner glazes that do not craze - and most can be
changed to stop the crazing at the mid to high firing levels.
Many potters will argue that it does not matter - mostly because they don't
know how to make the necessary changes.
There is probably some bacteria in those craze lines at least some of the
time - it depends on how the ware is cleaned - I don't think it is a
problem if food is eaten off that ware - it may even help keep our immune
system stronger. I do know that if fish is served on crazed ware it will
keep that smell for a long time.
I feel it may be a problem if food is stored on crazed ware - I think it
will go bad faster because of whats in the cracks - would it be
significant? I don't know. I wonder if anyone has done any experiments?
The big reason for eliminating crazing on functional work has to do with
how much easier it is to break crazed ware compared to uncrazed.
If a glaze is crazed and unstable - then it will leach more than uncrazed
simply because there is more surface for acids to work on.
RR
>Hi All,
> Even after 20 years working in clay and teaching it there is still a
>lot I don't know. Here is my question. I have worked in four public art
>centers as well as my own studio. In two out of the four public ones
>there were glaze/body fit problems that led to crazing. I was told and
>read that this usually leads to leaching out of glaze ingredients into
>food stored or cooked in said pots. Not only were students not told about
>this but the glaze ingredients were not available so one could figure out
>what exactly might be leaching into ones casserole of coffee.
> Needless to say, I warned all my students and anyone else who would
>listen. However, to the best of my knowledge, the one center has never
>done anything about this in spite of my remarks. The other place is
>fixing the issue even as I type.
> Am I just a paranoid alarmist? Shouldn't the one center limit the
>use of clay bodies and glazes to ones that fit each other for students
>making ware for food use?
> In other centers where commercially produced glazes are use can we
>take the label as it is printed that the glazes are safe when fired
>according to directions? I am guessing that the answer will be "Test!
>Test! Test!" but want to hear from all sides. I hope some of the
>commercial glaze makers are reading this because I would like to hear from
>them too. Thanks. --Kim H.
Ron Roy
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Lee Love on mon 7 jul 08
Update on my copper pennies experiment:
I have been putting filtered water in Kintaro's water bowl
in the kitchen, but no pennies like in the outdoor bowls, because
inside, there is no algae growth. But I noticed that Kintaro was
only drinking upstairs, from his water bowl in the bathroom (I don't
filter that water) and outside, avoiding the inside bowl.
I took a whiff and realized it smelled like mildew. Because the
water filter filters out chlorine, there was no inhibitors to keep the
mildew from forming. I will try pennies in the inside bowl to see
if it helps with indoor mildew, like it helps with algae in the
outdoor bowls.
--
Lee Love in Minneapolis
http://mashikopots.blogspot.com/
http://claycraft.blogspot.com/
"Let the beauty we love be what we do.
There are hundreds of ways to kneel and kiss the ground." --Rumi
Tony Ferguson on mon 7 jul 08
Lee,
This reminds me of (I was told the story) that folks would put a silver coin in their milk containers to make it last longer--being that silver destroys/inhibits bacterial growth.
Tony Ferguson
Lee Love wrote: Update on my copper pennies experiment:
I have been putting filtered water in Kintaro's water bowl
in the kitchen, but no pennies like in the outdoor bowls, because
inside, there is no algae growth. But I noticed that Kintaro was
only drinking upstairs, from his water bowl in the bathroom (I don't
filter that water) and outside, avoiding the inside bowl.
I took a whiff and realized it smelled like mildew. Because the
water filter filters out chlorine, there was no inhibitors to keep the
mildew from forming. I will try pennies in the inside bowl to see
if it helps with indoor mildew, like it helps with algae in the
outdoor bowls.
--
Lee Love in Minneapolis
http://mashikopots.blogspot.com/
http://claycraft.blogspot.com/
"Let the beauty we love be what we do.
There are hundreds of ways to kneel and kiss the ground." --Rumi
Tony Ferguson
315 N. Lake Ave. Apt 312
Duluth, MN 55806
...where the sky meets the lake...
Artist, Educator, Photographer, Film Maker, Web Meister
fergyart@yahoo.com
(218) 727-6339
http://www.tonyferguson.net
Lee Love on tue 8 jul 08
On Mon, Jul 7, 2008 at 2:14 PM, Tony Ferguson wrote:
> Lee,
>
> This reminds me of (I was told the story) that folks would put a
>silver coin in their milk containers to make it last longer--being
>that silver destroys/inhibits bacterial growth.
Folks are making good use of these metals in water purifiers and containers.
Sometimes the "old ways" make more sense than our beloved
"innovations." Linear thinking keeps us from seeing the web of cause
and effect.
--
Lee Love in Minneapolis
http://mashikopots.blogspot.com/
http://claycraft.blogspot.com/
"Let the beauty we love be what we do.
There are hundreds of ways to kneel and kiss the ground." --Rumi
Joseph Herbert on sat 12 jul 08
Copper, in the form of copper sulfate, is used to control algae in golf
course lakes. Since golf courses are really heavily fertilized, algae
blooms are a constant problem. Notice how blue the water looks. One rarely
sees fish in golf course lakes. Humm.
Joe
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG]On Behalf Of Ron Roy
Sent: Saturday, July 12, 2008 12:05 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Crazing Glaze vs. Safety
Silver is used in water purification all over the world - and has been for
some time. I have never heard of copper being used this way - look up
copper toxicity and you will see why it is not always a good idea.
RR
>On Mon, Jul 7, 2008 at 2:14 PM, Tony Ferguson wrote:
>> Lee,
>>
>> This reminds me of (I was told the story) that folks would put a
>>silver coin in their milk containers to make it last longer--being
>>that silver destroys/inhibits bacterial growth.
>
>Folks are making good use of these metals in water purifiers and
containers.
>
> Sometimes the "old ways" make more sense than our beloved
>"innovations." Linear thinking keeps us from seeing the web of cause
>and effect.
>
>--
> Lee Love
Ron Roy
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
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Lee Love on sat 12 jul 08
On Sat, Jul 12, 2008 at 1:05 PM, Ron Roy wrote:
> I have never heard of copper being used this way - look up
> copper toxicity and you will see why it is not always a good idea.
We have investigated copper Ron, but you only read what supports what
you already believe.
The original concern with copper is when it is used with lead or
other similar compounds.
Copper release has been measure in pure copper containers in a
study I have shared here, done in India. Only dietary levels of
copper can be detected in water held in these containers. (If you
are phobic about crazing, you might consider putting copper in the
glaze to kill bacterial.) Because Indians are switching from
traditional copper and brass water containers to plastic, they are
having trouble with their water and bacteria, especially if it is
stored out of the light.
Actually, our foods no longer provide the minimum dietary
requirements of copper because it is leached out of plants by
pesticides and fertilizer. This copper deficiency may be related to
Alzheimer's and BSE.
"Copper compounds used by potters are not considered much hazardous if
there is no ingestion of basic copper carbonate and/or the sulfate.
In glazes, copper enhances lead leaching. Good studio housekeeping is
always good practice. Avoidance of processes generating unnecessary
dust is also important and the wearing of an approved dust mask when
the exposure seems hazardous is also good practice."
Edouard Bastarache M.D. (Occupational & Environmental Medicine)
Author of " Substitutions for raw ceramic materials "
edouardb@sorel-tracy.qc.ca
http://www.sorel-tracy.qc.ca/~edouardb/
--
Lee Love in Minneapolis
http://mashikopots.blogspot.com/
http://claycraft.blogspot.com/
"Let the beauty we love be what we do.
There are hundreds of ways to kneel and kiss the ground." --Rumi
Ron Roy on sat 12 jul 08
Silver is used in water purification all over the world - and has been for
some time. I have never heard of copper being used this way - look up
copper toxicity and you will see why it is not always a good idea.
RR
>On Mon, Jul 7, 2008 at 2:14 PM, Tony Ferguson wrote:
>> Lee,
>>
>> This reminds me of (I was told the story) that folks would put a
>>silver coin in their milk containers to make it last longer--being
>>that silver destroys/inhibits bacterial growth.
>
>Folks are making good use of these metals in water purifiers and containers.
>
> Sometimes the "old ways" make more sense than our beloved
>"innovations." Linear thinking keeps us from seeing the web of cause
>and effect.
>
>--
> Lee Love
Ron Roy
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Lee Love on sun 13 jul 08
On Sat, Jul 12, 2008 at 11:17 PM, Joseph Herbert wrote:
> Copper, in the form of copper sulfate, is used to control algae in golf
> course lakes. Since golf courses are really heavily fertilized, algae
> blooms are a constant problem. Notice how blue the water looks. One rarely
> sees fish in golf course lakes. Humm.
Water filters both for drinking and chlorine free swimming pool
water use copper/zinc filters. You only have to look on the net to
find them. Copper metal releases less than dietary amounts of copper
into water. A well made copper glaze will release much less.
--
Lee Love in Minneapolis
http://mashikopots.blogspot.com/
http://claycraft.blogspot.com/
"Let the beauty we love be what we do.
There are hundreds of ways to kneel and kiss the ground." --Rumi
Ron Roy on wed 16 jul 08
WE have not investigated anything about copper toxicity Lee - the facts are
clear - everyone has different levels of copper in them, some people cannot
tolerate any copper - others have more then they need already and some
don't have enough. It depends on many factors.
Turns out that it's hard to keep copper in all kinds of glazes - it's why
we used copper to test our glazes to determine relative stability.
While it may be true that our foods are short of some minerals - and
supplementation is necessary - the doses should be controlled in a very
precise way. Certainly not with glazes - which release anywhere from very
little to comparatively large amounts.
It is not our job to be providing supplements from our glazes - that is
just an excuse for those who don't want to learn the skills necessary to
make stable glazes.
Anyone who wants to understand copper toxicity can do it easily - just
google copper toxicity - it's all there - including boiling milk in copper
pots can be deadly.
RR
>On Sat, Jul 12, 2008 at 1:05 PM, Ron Roy wrote:
>> I have never heard of copper being used this way - look up
>> copper toxicity and you will see why it is not always a good idea.
>
>We have investigated copper Ron, but you only read what supports what
>you already believe.
>
> The original concern with copper is when it is used with lead or
>other similar compounds.
>
> Copper release has been measure in pure copper containers in a
>study I have shared here, done in India. Only dietary levels of
>copper can be detected in water held in these containers. (If you
>are phobic about crazing, you might consider putting copper in the
>glaze to kill bacterial.) Because Indians are switching from
>traditional copper and brass water containers to plastic, they are
>having trouble with their water and bacteria, especially if it is
>stored out of the light.
>
> Actually, our foods no longer provide the minimum dietary
>requirements of copper because it is leached out of plants by
>pesticides and fertilizer. This copper deficiency may be related to
>Alzheimer's and BSE.
>
>"Copper compounds used by potters are not considered much hazardous if
>there is no ingestion of basic copper carbonate and/or the sulfate.
>In glazes, copper enhances lead leaching. Good studio housekeeping is
>always good practice. Avoidance of processes generating unnecessary
>dust is also important and the wearing of an approved dust mask when
>the exposure seems hazardous is also good practice."
>
>Edouard Bastarache M.D. (Occupational & Environmental Medicine)
Ron Roy
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Ron Roy on wed 16 jul 08
Depends on how acid the water is - any way - another reason not to drink
swimming pool water.
RR
> Water filters both for drinking and chlorine free swimming pool
>water use copper/zinc filters. You only have to look on the net to
>find them. Copper metal releases less than dietary amounts of copper
>into water. A well made copper glaze will release much less.
Ron Roy
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
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