Khaimraj Seepersad on fri 26 feb 99
Response is in the original letter , scroll down please . Thank you .
From Khaimraj Seepersad [ hobby - potter ]
-----Original Message-----
From: Peter Atwood
To: CLAYART@LSV.UKY.EDU
Date: 25 February 1999 5:44
Subject: hardness and leaching (long)
----------------------------Original message----------------------------
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?
*** Perhaps if you look at it from the washing wares aspect - plastic or
wire scrubber or fine particles in Vim , [ physical abrasion ] , chemicals
in the soap solution , balanced for less corrosion of the surface .
The difference between , Jadeite - somewhat glassy appearance [ mohs 6.5 to
7 ] soluble in Dil . Hcl , melting point 1060 deg. c . and Nephrite - waxy
appearance [ mohs 5.5 to 6.5 ] not soluble in Dil . Hcl , melting point
over 1200 deg. c. [ grossly simplified / notes from a book on Gems ].
State of fusion , temperature and type of bonds formed here are more
important , Alkalies to Silica form more easily broken bonds and Alkalines
to Silica form more insoluble bonds , Zro2 , Tio2 , are chemically fairly
inert and when bonded to Sio2 are very inert .
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.
*** Try from the aspect of bitterness , small quantities of copper will
unbalance wine , whiskey and I might add song , as well as juices . Read on
for glaze decay .
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.
*** Everytime a glaze is leached , holes appear in the matrix , and these
holes become tunnels in , and slowly your glaze decays . Aside, some enamels
seem to take this into account and use this quality . Some one correct me
please ? Is not a fired glaze , excessively magnified similar to the idea of
coloured marbles stuck
together where they touch . The exterior of your glaze being Silica rich ,
those oxides that are volatile [ Na20 , B203 ] leaving . Under that layer
you find softer layers [ not unlike teeth , except there is no saliva to
deliver
new building material ] .
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.
***scroll on
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.
*** Scroll on .
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.
*** Question - But what about the other sources of Copper , from food or
water ? Just because your family may have a high tolerance to Copper is it
wise to treat everyone in the same manner .
Perhaps , what Ms. Rossol and others are having to do is to make people
aware of these facts , so you can make educated decisions , hopefully
stimulating your desire to go out and read Patty's Industrial Safety , and
the Pharmocopoeia , a book every Pharmacist has .
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.
*** There are obviously some Oxides that are harmful even for the Potter to
use , some that are too harmful for use near Food , and others can only be
on decorative wares , but there's still a great deal of leeway where
creativity is concerned . There is no reason to have to use Copper oxide in
glazes on articles where food is concerned , you can always decorate the
exterior where it is safer on cups [ as long as your lip does not reach it ]
.. Plus , if you really appreciate Tea , for colour why not white , or soft
buff , or for a bitter free flavour .
--Peter in western mass wondering if he should put his tea in that
barium copper glazed cup...
______________________________________________________
Get Your Private, Free Email at http://www.hotmail.com
Dave Finkelnburg on sat 27 feb 99
Interesting! Very interesting! Peter, I agree the quantity of copper
leaching from your work probably isn't a huge issue. Whether to eat/drink
from a ceramic piece which leaches any metals in any quantity is a personal
choice in any event, certainly no business at all of the general public, let
alone the ceramic/clay art community.
At the same time, think about Alar. What has scientifically turned out
to be a relative non-issue for human health devastated the apple industry!
The reason was bad publicity. From a moral perspective, and also from a
very practical one, it doesn't make sense to me to knowlingly sell or give
anyone food ware that can leach any heavy metal, copper included. Someday
(the question is only when, not if) there arises a public furor (scare?)
over metal leaching from unregulated production of glazed ware, I want to be
in a position to assure those who do or would posess my ware that they have
ABSOLUTELY nothing to worry about.
Like you, Peter, I'm trying to be practical about this complex, often
emotional subject.
Dave
-----Original Message-----
From: Khaimraj Seepersad
To: CLAYART@LSV.UKY.EDU
Date: Friday, February 26, 1999 1:50 PM
Subject: Response to Mr. Peter Atwood - Subject Hardness and Leaching
>----------------------------Original message----------------------------
>Response is in the original letter , scroll down please . Thank you .
>>From Khaimraj Seepersad [ hobby - potter ]
>-----Original Message-----
>From: Peter Atwood
>To: CLAYART@LSV.UKY.EDU
>Date: 25 February 1999 5:44
>Subject: hardness and leaching (long)
>
>
>----------------------------Original message----------------------------
>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?
>
>*** Perhaps if you look at it from the washing wares aspect - plastic or
>wire scrubber or fine particles in Vim , [ physical abrasion ] , chemicals
>in the soap solution , balanced for less corrosion of the surface .
>The difference between , Jadeite - somewhat glassy appearance [ mohs 6.5 to
>7 ] soluble in Dil . Hcl , melting point 1060 deg. c . and Nephrite -
waxy
>appearance [ mohs 5.5 to 6.5 ] not soluble in Dil . Hcl , melting point
>over 1200 deg. c. [ grossly simplified / notes from a book on Gems ].
>State of fusion , temperature and type of bonds formed here are more
>important , Alkalies to Silica form more easily broken bonds and Alkalines
>to Silica form more insoluble bonds , Zro2 , Tio2 , are chemically fairly
>inert and when bonded to Sio2 are very inert .
>
>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.
>
>*** Try from the aspect of bitterness , small quantities of copper will
>unbalance wine , whiskey and I might add song , as well as juices . Read on
>for glaze decay .
>
>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.
>
>*** Everytime a glaze is leached , holes appear in the matrix , and these
>holes become tunnels in , and slowly your glaze decays . Aside, some
enamels
>seem to take this into account and use this quality . Some one correct me
>please ? Is not a fired glaze , excessively magnified similar to the idea
of
>coloured marbles stuck
>together where they touch . The exterior of your glaze being Silica rich ,
>those oxides that are volatile [ Na20 , B203 ] leaving . Under that layer
>you find softer layers [ not unlike teeth , except there is no saliva to
>deliver
>new building material ] .
>
>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.
>
>***scroll on
>
>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.
>
>*** Scroll on .
>
>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.
>
>*** Question - But what about the other sources of Copper , from food or
>water ? Just because your family may have a high tolerance to Copper is it
>wise to treat everyone in the same manner .
>Perhaps , what Ms. Rossol and others are having to do is to make people
>aware of these facts , so you can make educated decisions , hopefully
>stimulating your desire to go out and read Patty's Industrial Safety , and
>the Pharmocopoeia , a book every Pharmacist has .
>
>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.
>
>*** There are obviously some Oxides that are harmful even for the Potter to
>use , some that are too harmful for use near Food , and others can only be
>on decorative wares , but there's still a great deal of leeway where
>creativity is concerned . There is no reason to have to use Copper oxide in
>glazes on articles where food is concerned , you can always decorate the
>exterior where it is safer on cups [ as long as your lip does not reach
it ]
>. Plus , if you really appreciate Tea , for colour why not white , or soft
>buff , or for a bitter free flavour .
>
>--Peter in western mass wondering if he should put his tea in that
>barium copper glazed cup...
>
>______________________________________________________
>Get Your Private, Free Email at http://www.hotmail.com
>
Tom Wirt on sat 27 feb 99
>>> My father is a
>plumber and spends his days soldering copper pipes in enclosed basements
>with little ventilation. He's doing fine.
Normally I wouldn't enter a discussion on the safety issues of glazes, etc.
But this one comment caught my eye.
And while I'll admit to being generally in the camp of, "he's doing fine"
even though constantly exposed, several recent events are changing my mind.
I suspect, hell, we know, that the effects of many of these exposures occurs
over many many years. One of the reasons we don't see the effects is that
the time frame hasn't been long enough. Pottery hit it's recent heyday in
the mid-'60's. barely 30 years ago. Those cases of silicosis, manganese
and maybe other poisonings are just starting to show up.
So, yup, he's in there soldering everyday with no apparent ill effects.
What happens in 20 or 30 years? Just like global warming. By the time we
see the symptom, it may be too late (read Lovelock and Margulies' "The Gaia
Hypothesis").
Tom Wirt
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