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copper toxicity

updated fri 18 jan 08 on sun 15 jun 97

Says Clay Times Poster: glaze containing more than %3 of copper is toxic and
should not be used on food utensils.Is this another unbreakable commandment
or are there exceptions?What do Clayart's learned men and women say to this?

Jiri in Berkeley

Tom Buck on sun 15 jun 97

Since copper is an essential element for some of the body's enzyme
systems, and since many texts recommend one consume 1000-3000 micrograms
of copper daily to make up for losses in urine, then one can say that a
smooth-surfaced glaze will not likely release that level of copper into
acidic foods, especially a glaze that has appropriate amounts of alumina
and silica for the firing temperature. And further, since copper oxide is
an excellent flux, any amount up to 6% will probably be well incorporated
into the glaze's glass matrix.

Tom Buck (new email address: )
Hamilton, Ontario, Canada

On Sun, 15 Jun 1997 wrote:

> ----------------------------Original message----------------------------
> Says Clay Times Poster: glaze containing more than %3 of copper is toxic and
> should not be used on food utensils.Is this another unbreakable commandment
> or are there exceptions?What do Clayart's learned men and women say to this?
> Jiri in Berkeley

Peter Jackson on wed 18 jun 97

What about handling glaze with copper oxide in it? Should rubber gloves be
worn to keep copper from being absorbed into the skin?

Peter Jackson

Peter Atwood on sun 28 feb 99

Well folks, I thought that I had better put my money where my mouth is
and back up my assertions of the relatively benign nature of copper
exposure from glazes. So I went out on the net and looked some stuff up
in books and here is what I found out:

1) According to the OSHA website it takes about 23 grams of copper
INGESTED to kill a 150 lb person. It takes 30 minutes of continuous
exposure of airborne spray or dust in a concentration that I didn't
write down but which sounded pretty high to kill you. OSHA does not
consider copper exposure in the workplace to be a significant problem
and they say exactly that on their website. At worst, they state that
copper is an irritant especially airborne. If I remember correctly
that's pretty much what Monona Rossol wrote in her Artist's Safety book
although she didn't get into specific toxic levels.

2) Zinc and vitamin C cause the body to excrete copper and taking
megadoses of these products will generally result in copper deficiency.
So maybe washing that zinc lozenge down with that orange juice in your
Oribe cup is not going to be enough to replenish your stores after all.
The average adult has 150 mg of copper in their body.

3) The US RDA for copper is 3mg although I saw figures vary quite a bit
as to what is considered a safe dosage. Most doctors seem to agree that
for someone who is copper depleted a daily dosage of 10 mg for a period
of one month is not unsafe with a daily dosage of 5 mg following. It is
believed that some 90 percent of Americans are copper deficient.

4) Estrogen increases the amount of copper your body can absorb so women
taking oral contraceptives or hormone replacement therapy will be able
to take in more.

5) Copper has several roles in the body one of which is to keep the
connective tissues intact. It is believed that the reason for wearing
copper bracelets by arthritis sufferers is that the copper absorbed
through the skin by sweating has a positive effect on these connective
tissues. Copper also plays an essential role in the production of
elastin which is what keeps our skin soft and supple and wrinkle free.

6) For those who think copper is a heavy metal, it is not. In fact
copper inhibits the uptake of heavy metals such as lead and cadmium. It
turns out that there are a limited number of ionic channels in your
stomach and if there is competition for these channels then less uptake
is the result. This is also the reason for chelated minerals. Minerals
in their regular oxide form often have difficulty in being taken into
the body so manufacturers have developed these chelated forms in which
the mineral is bound to an amino acid, something which the body
recognizes and can easily absorb. Also food in your stomach will
interfere with the absorption of copper.

7) Copper deficiency results in an increase of LDL cholesterol and a
decrease in HDL cholesterol. It also has an effect on glucose levels by
affecting insulin production but I can't remember specifics on that one.
The upshot was a negative effect on glucose levels.

8) Wilson's disease is the disease that people have who cannot excrete
copper from their bodies. It is often found in people who have married
their brothers or sisters but, as a genetic flaw, it could also be
found in other populations.

9) The foods rich in copper include chocolate, nuts, peanut butter,
liver, oysters and crab. Yum!

Now, when I consider the positive, indeed ESSENTIAL effects that copper
has I have to say that I am not worried about my Oribe glaze causing
copper poisoning. In light of this I would propose that making
comparisons between copper exposure and lead exposure are not valid. A
number of people have written to me saying that it used to be thought
that lead wasn't a significant hazard and now it is proved that it is
and so it's better to be safe in regards to copper. Well, I don't know
of any benefit to the body from lead so I really think that that kind of
argument is spurious.

Copper leaching can cause other effects such as a color change to the
glaze and that would not make me happy. A friend has recently mentioned
seeing an article somewhere saying that the Shaner's Oribe is a leacher
and that it can change color if it has a prolonged exposure to acidic
foods. Has anyone on the list experienced this? If so I'd like to know
so that adjustments could be made to make this lovely glaze more

--Peter Atwood

Get Your Private, Free Email at

David Hendley on mon 1 mar 99

I can't remember the figures, and they are down at the office,
but I can tell you that the great state of Texas is concerned
about copper exposure.

In my capacity as a director of a small community water system,
I am required to test homes for possible excess copper in water.
The regulations progulmate that we try to identify 10 houses
that might likely have high levels of copper. First on the list
is older houses with copper plumbing and lead solder, next is
newer houses with copper pipes.
We are a tiny utility. Larger systems have to test more.
The residents of any houses with high readings must be notified.
I'm no fan of more and more government regulations, but there
must have been some health problems from copper, somewhere
in Texas, to prompt this testing requirement.

Peter, I appreciate your candid discussion of copper leaching.
I do believe, however, that the only responsible action for
a potter is to try to formulate glazes that do not leach anything,
be they harmful or beneficial minerals or elements, unless
customers are informed that this will happen.
Come to think of it, this may be a marketing idea - pottery
and vitamins & minerals in one:
"Forget the Total cereal, get your all you need from the bowl!"
"It's a bowl... no, it's a vitamin,'s BOTH! The RONCO
two-in-one bowl and mineral suppliment! Be the first on
your block. Call now!"

David Hendley
Maydelle, Texas

Merrie Boerner on mon 1 mar 99

I am concerned about the affects of copper on the potter as he works. I
use a copper wash on some of my pieces. I paint copper carb. mixed with
water onto leaf impressions and sponge it off. When fired, this makes the
veins of the leaves and other impressions black if if
glazed with white or light colored glazes. Even though the copper is moist
while I work , after several hours, I can taste it. And I can smell it. It
must be in the air. I get a strange sensation in the bridge of my
nose......Also, I developed an irritated place on the white part of my eye.
My ophthalmologist examined my eye and said that it was irritated by dust
or wind....I knew that it began in my I ordered "the
Artist's Complete Health and Safety Guide" to investigate. According to
this book you may develop these symptoms when exposed to a very small
amount of copper. Here is a quote from the book: " LOCAL: Irritates and
discolors the skin. Respiratory tract irritant. Repeated inhalation of dust
can cause sinus congestion and ulceration, and perforation of the nasal
septum. Contact with eyes can cause conjunctivitis and discoloration and
ulcers of the cornea. SYSTEMIC: May cause allergies in some people.
Inhalation of fumes can cause metal fume fever (flu-like symptoms).
Absorption can cause nausea, stomach pains."
Now I'm not fussy about germs or fact, I thought "a spoon
full of dirt a day" for my kids would make them did. However,
since reading this warning, I have been far more careful about ventilation
and protection for my body's sake in the studio. You know, when some of us
began this clay endeavor, we were young and had that invincible
feeling...never realizing how quickly time would fly, or how many chemicals
we would ingest. Hopefully the young ones reading will learn from us. I
would hope that they will learn that getting old in clay is an exciting
lifetime worth taking care of yourself for ! Merrie in
No, I'm not going to have a mid-life crisis ! I'm building a wood-firing
kiln !!!!

Mike Gordon on tue 2 mar 99

The question is--- after they find some kind of copper leaching from
copper pipes, with or without lead solder --- what do they recommend you
switch to???Plastic?? Mike

Mike Gordon on tue 2 mar 99

The question is--- after they find some kind of copper leaching from
copper pipes, with or without lead solder --- what do they recommend you
switch to???Plastic?? Mike

"Gavin Stairs (by way of Gavin Stairs on tue 2 mar 99

At 01:40 PM 2/28/99 EST, Peter Atwood wrote:
>----------------------------Original message----------------------------
>Well folks, I thought that I had better put my money where my mouth is
>and back up my assertions of the relatively benign nature of copper
>exposure from glazes. So I went out on the net and looked some stuff up
>in books and here is what I found out:

Peter, I have a strong opinion about this sort of thing. In my view,
potters should not be in the business of dispensing dietary supplements by
way of leaching pottery. It is an ill controlled, ill conceived notion
that we should avoid. That the material so dispensed is or is not
poisonous is not really the point. The general expectation of a person who
buys a pot must be that the pot will not gradually dissolve into their
food, at least over the lifetime of the pot or themselves.

If a potter makes a pot like the one you have described for their own use,
it is up to them whether they use it or not, and under what circumstances.
If they sell or give that pot to a member of the public, they are putting
it in the hands of someone who may not appreciate the circumstances, and
who may use it in a manner not intended, and which may not be appropriate.
When this involves the release of a toxic material, this is a gross
negligence or incompetence that deserves at the very least a reprimand and
correction. If this involves innocuous material, as in most cases would be
true with copper, it is merely an indication of disregard for and
disrespect for the due expectations of the person who ends up using the
pot. Whatever the law might be, I would consider it a breach of implied
contract of serviceability.

Now a few comments that come to mind:

In past, when copper pots were common, cooks knew the effect of copper on
food. The better made pots of more recent vintage were tin coated on the
inside, food contact surface in order to avoid imparting a copper taste to

In most circumstances, it appears that clear, non-lead, NaK/CaMg/P/Sn base
glazes, and colored glazes using iron, copper, zinc, titanium and cobalt
are relatively non-toxic for the end user, although there have been some
documented exceptions. Virtually all other colorants plus lithium should
be treated with respect as potential problems. Let me try to be a bit more

As used in glazes, the following materials (elements) are:

Noble metals (non-toxic): Au, Ag, Re, Os, Ir, Pt, Rh
Inert (non-toxic): Si, Al, B, O, Zr, Ti, P, Zn
Inoccuous, normally volatile: C, N, S
Inert fluxes (non-toxic): Na, K, Ca, Mg
Halide fluxes (fugitive, probably non-toxic, but may promote mobility): Cl, F
**Active fluxes (may be toxic in some cases): Li, Ba
*Less toxic colorants: Fe, Co, Cu
**More toxic colorants: V, Mn, Ni, Mo
***Toxic fluxes: Pb, Cd

* means safe under most circumstances with a normally durable base glaze,
although Cu is more difficult than the others and may have side effects in
** means testing should be normal to assure that the material is not
leaching from the glaze.
*** means that testing is mandatory in many countries, and most studio
potters are well advized to avoid these altogether.

The ** elements are the most troublesome, as they are hard to avoid in
making some colors.

I think these are the most used ones. If anyone has any modifications to
this list, I'd be interested to hear about it.

As to what is or is not a heavy metal, to an astronomer, everything but H
and He are metals. To a potter, everything but the light elements and the
fourth line transition elements should probably be considered a heavy
metal. That does not include many problem metals, like vanadium, and
chromium, and does include many that aren't a problem, like zircon and the
noble metals. Better just to go by the toxicity. For instance, Beryllium,
the second lightest metal, is poisonous as metal and oxide.


David Hendley on thu 4 mar 99

At 04:15 PM 3/2/99 EST, you wrote:
>----------------------------Original message----------------------------
>The question is--- after they find some kind of copper leaching from
>copper pipes, with or without lead solder --- what do they recommend you
>switch to???Plastic?? Mike
That's the "beauty" of government regulations: They have more
questions than answers.
As Celia in North Carolina said, they give you some ways to lessen
the problem. They tell you is to run your faucet for 30 seconds
before using the water, especially in the morning, since the water
has been in the pipes all night. Never drink or cook with water
from the 'hot' tap. Things like that.

My personal 'gut' feeling (I hope that feeling is not from copper exposure)
is that, in my house, I'd much rather stick with an ancient and natural
material like copper than switch to plastic pipe. PVC plumbning has only
been in use for a few decades, not long enough to adequately observe
any long-term unexpected effects, in my opinion.

David Hendley
Maydelle, Texas

claypots on fri 5 mar 99

Have you ever smelled the water that comes from a PVC pipe which has not =
turned on in over 24 hrs? Definitely something I wouldn't want to drink
from--it has a strong chemical smell.

Ron Roy on thu 17 jan 08

Potters should not be in the business of providing heavy metals to their

If there are deficiencies the correct way to address the problem is with
controlled doses.

In the meantime I would advise you not to use a degradable copper glaze in
a bird bath - at least not without doing the necessary research to find out
if it is safe for the birds and others creatures that drink from puddles.

By the way - one of the factors in copper deficiencies is zinc - there is
pleanty of information on the toxicity of copper by the way - just google
copper toxicity.


>On 1/14/08, Ron Roy wrote:
>> I see birds drinking from our bird baths - I wonder how
>> much dissolved copper birds can handle before they are affected?
> Because of pesticide and fertilizer leaching copper out of our
>soil, we are all facing copper deficiencies. Factory raised food
>does not have the dietary copper in it we require for a healthy
>nervous system. As we know with the Bald eagle, these pesticides
>also effect wildlife. These copper deficiencies may be implicated in
>neurological diseases BSE and Alzheimer's
> In the study I provided earlier, which examined sickness
>caused by drinking water, because folks in India switching from
>traditional copper and brass water containers to plastic, the amount
>needed to keep bacteria from forming, causes less than the daily
>requirement of copper in the human diet. *I provide the article from
>the archives below.
> If we can look at this topic rationally, we can make good use
>of our materials for different purposes:
>As Edouard has said: "Je n'ai pas peur de mon ombrage"
>/"/*The amounts that circulate into the brass water vessels would not
>harm humans, Reed adds. According to the researchers, even a person
>drinking 10 litres of such water in a single day would take in less than
>the daily recommended dose of copper or zinc.*/ "
>/*Drinking water stored in brass vessels good for health
>Brass jugs polish off disease
>Roxanne Khamsi
>Traditional pitchers beat plastic in safe water stakes.
>Brass water containers could combat many water-borne diseases, according
>to microbiologists. The discovery suggests that these vessels should be
>used in developing countries, where people typically view cheaper
>plastic containers as the better option.
>Water-borne diseases remain a serious threat in many poor regions of the
>world, with around 2 million children dying each year from diarrhoea.
>Efforts to provide safe drinking water have had difficulty reaching
>remote areas.
>Even in places with basic water-purification systems, people often opt
>for riskier wells under trees because the water is cooler, says Rob
>Reed, who led the brass study. On a recent trip to India, Reed, a
>microbiologist at Northumbria University in Newcastle upon Tyne, UK,
>witnessed villagers doing exactly this.
>But he also heard an interesting piece of local wisdom: people believe
>that traditional brass water containers offer some protection against
>sickness. The idea intrigued Reed, who was in Asia investigating the
>antibacterial effects of sunlight on water.
>He has now found that bacteria are indeed less likely to thrive in brass
>water pots than in earthenware or plastic ones. "It's one of the
>traditional ideas of water treatment and we were able to find a
>microbiological basis for it," he says...
>...Plastic beliefs
>Brass water pots also easily outperformed plastic ones, the researchers
>discovered. Plastic, says Reed, did not inactivate the bacteria. But
>many people in developing nations use plastic drinking vessels, because
>they view them as more modern...
>...Although Reed declines to speculate about exactly how many lives
>could be saved by switching to brass, he points to the millions of lives
>claimed each year by water-borne diseases. Storing water in brass for
>two days could stop this, he suggests: "The potential is great."
>Lee in Mashiko, Japan
>"Men are born ignorant, not stupid. They are made stupid by
>education." -- Bertrand Russell
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Ron Roy
15084 Little Lake Road
Brighton, Ontario
K0K 1H0