Peter Atwood on thu 25 feb 99
Well folks, I never seem to run out of questions. That's one of the
great pleasures of this clay business. I tend to be the sort of person
who enjoys learning new things and the more I study this stuff and make
pots, the more I realize that I could spend a lifetime and still never
run out of things to discover.
I thought I'd check out those hardness pens from that Idaho Mining
company and I've scratched a few of my glazes. Most of my ^10 glazes
seem to average in the 6-7 range although one was about 5. My question
is, would a harder glaze be more durable and would a more durable glaze
tend to leach less metals?
As an aside, I have to confess that I am not really overly concerned
about copper leaching from my glazes even though I use Shaner's Oribe on
some of my pots and a weathered bronze, both of which are probably
leachers.
This is probably going to get me in trouble but I have to say it. I
think that copper is not really a big deal and I know that many of you
will be having fits reading this. But I challenge you to show me any
evidence that copper from pots is having an ill effect on any one. Even
if a glaze is leaching 20 or 30 or even 40 ppm in the tests how much is
actually leaching in real day to day usage? As I understand it, the
tests involve 24 hours of standing in a vinegar-strength solution.
Perhaps I am wrong about the specifics of the tests. There are those of
you out there who will be quick to correct me I'm sure.
My point is that if you drink a cup of coffee in a mug glazed in Oribe
fired to ^10 you will not be getting 40ppm of copper leaching out of it.
Even if did leach that amount one time you would not get it every time
for the life of the cup because there has to be a diminishing amount of
metal to be leached. I'm not even sure how many total mg of copper there
is in the surface area of the inside of a Shaner's Oribe glazed mug but
I doubt if it's very much. And I don't know of anyone who makes orange
juice in a ceramic pitcher although maybe there are those who do and I
admit that we can't control what people do with our pots after they are
sold.
As my chemist uncle pointed out, 20ppm is equal to 5 mg of substance in
a liter of solution. He recently tested the water in his lab in Boston
and found that the pipes were leaching 10-20 ppm of copper. He's not too
worried.
My wife's multivitamin lists 2 mg of copper as an ingredient. She shows
no signs of copper poisoning even though she routinely washes her
vitamin down with a glass of water from our copper pipes. My father is a
plumber and spends his days soldering copper pipes in enclosed basements
with little ventilation. He's doing fine. My grandfather before him
spent years in the business and is 83 and in reasonably good health.
Our bodies need a certain amount of these substances but certainly there
is a toxicity associated with some of them. Individuals are different
and I know that in the case of copper there are a very rare few whose
metabolisms cannot get rid of copper. Those people develop mental
illness and get a characteristic ring around their pupils.
Interestingly, those of you who are taking zinc for your colds should be
aware that zinc leaches copper from your body and so you will need to
supplement your diet. Might I suggest taking that zinc tablet with some
orange juice in a nice Oribe cup?
Copper is not lead and it is not Uranium. I think that it is wise to
seek ways to minimize excessive exposure to toxic substances and to
potentially toxic substances but it is not likely that drinking from an
Oribe cup is going to cause death.
Well, I feel a lot better now that I've aired my views towards the
leaching alarmists. Now I'm preparing for the inevitable onslaught of
the dissenters. I'm sure Monona shall take me to task and perhaps a few
others but surely there must also be among you a few with some common
sense? And perhaps some insights that I have missed. I am open to
learning as I said above and if someone can point out where I have gone
astray I'll gladly listen.
--Peter in western mass wondering if he should put his tea in that
barium copper glazed cup...
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Ron Roy on sun 28 feb 99
Hi Peter,
Aside from the possible effects of having too much copper in you - and I
don't think copper is a serious problem - but you should know the symptoms
in case you think you are having an adverse effect.
There are three other factors. Copper can affect the taste of foods, it can
lower the durability of a glaze and thereby increase release of other
toxins if present and - that glaze can discolour under some conditions -
imagine what that does to sales.
The general public will draw their own - not necessarily intelligent -
conclusions when ware does not appear to be stable - if you earn your
living from making pots it would be best to avoid unstable glazes.
RR
>----------------------------Original message----------------------------
>As an aside, I have to confess that I am not really overly concerned
>about copper leaching from my glazes even though I use Shaner's Oribe on
>some of my pots and a weathered bronze, both of which are probably
>leachers.
>
>This is probably going to get me in trouble but I have to say it. I
>think that copper is not really a big deal and I know that many of you
>will be having fits reading this. But I challenge you to show me any
>evidence that copper from pots is having an ill effect on any one. Even
>if a glaze is leaching 20 or 30 or even 40 ppm in the tests how much is
>actually leaching in real day to day usage? As I understand it, the
>tests involve 24 hours of standing in a vinegar-strength solution.
>Perhaps I am wrong about the specifics of the tests. There are those of
>you out there who will be quick to correct me I'm sure.
>
>My point is that if you drink a cup of coffee in a mug glazed in Oribe
>fired to ^10 you will not be getting 40ppm of copper leaching out of it.
>Even if did leach that amount one time you would not get it every time
>for the life of the cup because there has to be a diminishing amount of
>metal to be leached. I'm not even sure how many total mg of copper there
>is in the surface area of the inside of a Shaner's Oribe glazed mug but
>I doubt if it's very much. And I don't know of anyone who makes orange
>juice in a ceramic pitcher although maybe there are those who do and I
>admit that we can't control what people do with our pots after they are
>sold.
>
>As my chemist uncle pointed out, 20ppm is equal to 5 mg of substance in
>a liter of solution. He recently tested the water in his lab in Boston
>and found that the pipes were leaching 10-20 ppm of copper. He's not too
>worried.
>
>My wife's multivitamin lists 2 mg of copper as an ingredient. She shows
>no signs of copper poisoning even though she routinely washes her
>vitamin down with a glass of water from our copper pipes. My father is a
>plumber and spends his days soldering copper pipes in enclosed basements
>with little ventilation. He's doing fine. My grandfather before him
>spent years in the business and is 83 and in reasonably good health.
>
>Our bodies need a certain amount of these substances but certainly there
>is a toxicity associated with some of them. Individuals are different
>and I know that in the case of copper there are a very rare few whose
>metabolisms cannot get rid of copper. Those people develop mental
>illness and get a characteristic ring around their pupils.
>
>Interestingly, those of you who are taking zinc for your colds should be
>aware that zinc leaches copper from your body and so you will need to
>supplement your diet. Might I suggest taking that zinc tablet with some
>orange juice in a nice Oribe cup?
>
>Copper is not lead and it is not Uranium. I think that it is wise to
>seek ways to minimize excessive exposure to toxic substances and to
>potentially toxic substances but it is not likely that drinking from an
>Oribe cup is going to cause death.
>
>Well, I feel a lot better now that I've aired my views towards the
>leaching alarmists. Now I'm preparing for the inevitable onslaught of
>the dissenters. I'm sure Monona shall take me to task and perhaps a few
>others but surely there must also be among you a few with some common
>sense? And perhaps some insights that I have missed. I am open to
>learning as I said above and if someone can point out where I have gone
>astray I'll gladly listen.
Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849
Web page: http://digitalfire.com/education/people/ronroy.htm
Evan Dresel on sun 28 feb 99
Although I am not overly worried about copper leaching I don't know how
your chemist uncle figures 20 ppm is equal to 5 mg in a liter.
20 ppm is equal to 20 mg per liter. You see a liter of water weighs 1
kg or 1,000 g or 1,000,000 mg. So 20 mg per liter is 20 mg per
1,000,000 mg or 20 parts per million. If you really want to get picky,
the density of water changes with temperature and it is really per liter
of solution, not liter of water so the other dissolved things factor in,
but it is darn close even if you are talking sea water. That's why I
personally don't like talking ppm -- sloppy. Just say "mg/L".
-- Evan in W. Richland WA who makes a living looking at tiny amounts of
stuff in water.
Peter Atwood wrote:
>
> ----------------------------Original message----------------------------
snip...
>
> As my chemist uncle pointed out, 20ppm is equal to 5 mg of substance in
> a liter of solution. He recently tested the water in his lab in Boston
> and found that the pipes were leaching 10-20 ppm of copper. He's not too
> worried.
snip...
>
> --Peter in western mass wondering if he should put his tea in that
> barium copper glazed cup...
>
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