Peter Atwood on tue 18 apr 00
Hi John,
Really glad you responded to my leaching question. It is a shame that
testing is so expensive because it would be nice to have some more concrete
data to look at. Also, I think many people are very grateful that you are
spending the time and money to do the testing that you are doing. There is
one big question, however, that remains.....
You wrote:
...........................................
I once did a calculation of how long this leaching could go on.
I don't
remember the exact numbers anymore; however there is enough
glaze on a
typical piece of pottery for it to go on for a long time. For
example,
if there are 10 grams of glaze containing 5% copper carbonate on
the
inside of a mug, it contains about 0.3 gr of copper. If that
leaches at
10 mg/l into, say, 200 ml of liquid in the cup you only leach
out 2 mg
with each leaching. That gives enough copper (and/or glaze??)
for 150
leachings. Of course the reality is that even if the cup
leaches 10 mg/l
in the standard test, it will probably leach less than 0.5
mg/liter (or <
0.1 mg per cup of coffee) in normal coffee drinking use. That
0.3 grams
originally in the mug ought to be good for more than 3000 cups
of coffee
at that rate. And far more if what you suggest is the actual
case. And
of course, we now know we can make at least some glazes
containing 5%
copper carbonate that leach significantly less than 10 mg/l in
the
standard test.
.................................................
My big question is, if the reality is that a glaze that is leaching 10 mg/l
of copper in the standard leach test is only leaching .5mg/l in the real
life cup of coffee then why are we even having this discussion? That amount
sounds like dietary supplement to me. In fact I think I'll go have a couple
of cups of coffee in my favorite Oribe cup right now:)
Seriously, if real life leaching amounts are so low, then why the big to do?
I understand that the level of awareness needs to be raised so that people
will not produce ware that is changing color or leaching tons of barium and
the like. But don't you think that it is sometimes going a little too far?
I do see now why your statement in the past that you would like to produce
glazes that leach under the 10 mg/l amount makes sense. If that glaze is
only putting out .5 mg/l in real life then that is an acceptable amount. Was
this the glaze that was NOT cased with the clear glaze? I seem to also
recall that you had tested the same glaze with a clear over it and had
significantly reduced leaching.
BTW, I did test several of your glazes on your website and had some pretty
good results. The Fall's Creek Shino was very nice and craze free. Also the
green glaze, Frog Pond Green?, was also very attractive. For fun I tested
them at Cone 10 ten reduction as well as the Cone 6 oxidation and they were
still nice although the green burned off and went to the brown family.
Thanks for all your contributions!
Peter Atwood
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John Hesselberth on wed 19 apr 00
Peter Atwood wrote:
>My big question is, if the reality is that a glaze that is leaching 10 mg/l
>of copper in the standard leach test is only leaching .5mg/l in the real
>life cup of coffee then why are we even having this discussion? That amount
>sounds like dietary supplement to me. In fact I think I'll go have a couple
>of cups of coffee in my favorite Oribe cup right now:)
>
>Seriously, if real life leaching amounts are so low, then why the big to do?
>I understand that the level of awareness needs to be raised so that people
>will not produce ware that is changing color or leaching tons of barium and
>the like. But don't you think that it is sometimes going a little too far?
Hi Peter,
Thanks for your comments and your support of my work. I guess there are
several reasons why I continue to want to learn how to make glazes more
stable--even though I believe it is very unlikely we are causing any harm
with most, or maybe all, current glazes.
First, the coffee example is not the worst I can think of. The same
glaze might well be used in a casserole in which a tomato-based dish is
cooked. That might really get the copper level into the range where it
was affecting taste and, therefore, function if not health.
Second I believe there is a range of leaching lower than the vinegar test
will detect, but high enough to cause a pot to fade and pit over the
first few months or years of use. This again is an issue of function and
craftsmanship. I want us to make pots durable enough to have a long
useful life.
Next, I really am not in the business of providing food supplements. I
think people expect pottery to be inert and are entitled to have it that
way or as nearly so as we can make it. And there is always the hysteria
factor. Dave Finkelnburg said it well at our NCECA glaze stability
session. If the public or press becomes aware of a potter/glaze where
leaching is really bad, it can turn into a public relations nightmare
very quickly. All of a sudden facts or science have no meaning in that
kind of situation. Dave reminded us of the Alar(sp?) on apples fiasco a
few years ago. Something like that could negatively impact all of us a
lot.
Fourth, there is still some chance some potters are harming people with
badly leaching glazes--there is little question that some are providing
unrealized "food supplements"--see my final paragraph for a specific
example which is probably not good. As analytical tools become better,
medical science is becoming better at defining cause and effect
relationships. I'd rather help lead us to the land of stable, attractive
glazes now so there is no chance of us being on the firing line for
something like that.
Last, but not least, I am having a great deal of fun doing it. It is a
great adjunct to my pottery to force me to keep the logical side of my
brain functioning. It is a mystery that needs solving. It's my version
of climbing a mountain I guess: because it's there. My first career was
one of science and engineering and I'm not able to totally give that up
for the arts. On a personal level, I guess it is my way of trying to
give something back to my chosen second career which has given so much to
me.
In the end, though, I think this is something every potter needs to make
up their own mind on and, having made it up, have the knowledge available
to help them move in the direction they want to. I don't think new
regulations are needed; I try to use the word "goal" when discussing
this, not regulation or standard. I do think our awareness of the issue
needs to be high enough that we can make informed decisions as we design
our glazes and make and sell our pots.
By the way, if that is Shaner's Oribe you are going to drink your coffee
out of, recognize it is a pretty bad leacher. Tom Wirt and Betsy Price
had it tested and found it leached over 50 mg/l. Now you're up to 25% of
the Recommended Daily Allowance for copper with each cup.
---
Was
this the glaze that was NOT cased with the clear glaze? I seem to also
recall that you had tested the same glaze with a clear over it and had
significantly reduced leaching.
---
I used the 10 mg/l as an example only. I have seen copper containing
glazes that leach anywhere from 3-50 mg/l without a clear overcoat. Yes,
an overcoat of a clear, stable glaze can cut that down by up to a factor
of 10.
---
BTW, I did test several of your glazes on your website and had some pretty
good results. The Fall's Creek Shino was very nice and craze free. Also
the
green glaze, Frog Pond Green?, was also very attractive. For fun I tested
them at Cone 10 ten reduction as well as the Cone 6 oxidation and they
were
still nice although the green burned off and went to the brown family.
---
Thanks to Diane Woloshyn for having Falls Creek Shino tested and sending
me the results. Frog Pond Green is a great glaze up to about 3.5% copper
carbonate. After that it starts to leach more than I like. For a more
stable, similar glaze try Xavier's Warm Jade Green tested and contributed
by Heidi Haugen.
Regards, John
John Hesselberth
Frog Pond Pottery
P.O. Box 88
Pocopson, PA 19366 USA
EMail: john@frogpondpottery.com web site: http://www.frogpondpottery.com
"Pots, like other forms of art, are human expressions: pleasure, pain or
indifference before them depends upon their natures, and their natures
are inevitably projections of the minds of their creators." Bernard
Leach, A Potter's Book.
Gavin Stairs on wed 19 apr 00
At 03:39 PM 4/18/00, Peter Atwood wrote:
>...Seriously, if real life leaching amounts are so low, then why the big
>to do?
>I understand that the level of awareness needs to be raised so that people
>will not produce ware that is changing color or leaching tons of barium and
>the like. But don't you think that it is sometimes going a little too far?
...
Hi Peter,
The answer to this is simple: the standards are set so as to protect
people who do not understand, or forget, and who may use the pot in a way
that will leach spectacularly well, and contribute significant doses of
leached substance over a long time. An example given is of a child who was
poisoned by being served orange juice every day in a mug which leached. I
can't remember what the toxin was, but it was apparently toxic enough to
make the child ill.
This means that for the vast majority of us, virtually any pot which
doesn't fall apart in our hands is probably safe enough. Except if we use
it daily as our coffee or tea mug... or store juice in it... get the
idea? In Canada, the regulatory authorities reckon that any pot without a
hole in it may be used in such a manner as to leach in the standard
fashion. Maybe someone will feel that it is just the thing to keep salad
dressing in...for a month or so.
For myself, I figure that any pot that passed a rudimentary durability test
is ok for simple use, perhaps as a soup bowl. For sale, I would definitely
not make any such assumption, because I don't know what the buyer will do
with it. For a food storage bowl, or for an everyday use bowl, I insist on
a durable, non-toxic glaze; a liner glaze. I don't use the Mexican lead
glaze bowl for acid food. But I know people who have no such
discrimination, and who would cheerfully use a badly formulated lead glaze
pot to keep lemon juice or salad dressing in. So for my own peace of mind,
I would not make a liner glaze with any toxic oxides, and test for leaching
anyway, as a durability test.
Gavin
amy parker on mon 24 apr 00
Has anyone considered the extra leaching that might occur with the old
"office coffee cup"? I had a woman working for me once who never ever used
soap in her cup - just rinsed it out every day with a quick burst of tap
water & filled it again... The only time her cup ever got washed was when
she went out of town for two weeks and the person at the next desk got
grossed out by the accumulating culture(s).
Amy
amy parker Lithonia, GA
amyp@sd-software.com
Gavin Stairs on tue 25 apr 00
At 01:25 PM 4/24/2000 -0400, Amy wrote:
>----------------------------Original message----------------------------
>Has anyone considered the extra leaching that might occur with the old
>"office coffee cup"? I had a woman working for me once who never ever used
>soap in her cup - just rinsed it out every day with a quick burst of tap
>water & filled it again... The only time her cup ever got washed was when
>she went out of town for two weeks and the person at the next desk got
>grossed out by the accumulating culture(s).
Hi Amy,
I don't think the rinse and refill routine is bad for leaching. Rather the
opposite, as no alkaline detergents get to attack the cup. But the problem
of daily, continual use is the worst case phenomenon to which leaching
standards are directed. So the office coffee mug is a prime candidate for
leaching of nasties.
Most office mugs of the 80mm diameter by 90mm height variety are made in
high volume by a factory, probably by dry pressing or slip casting. They
are therefore likely to be subject to periodic testing. However, they
could well be lead glazed. Unfortunately, there are large numbers of
manufacturers, so I suspect it is not easy to confirm that they are all
compliant without testing many mugs.
If you use such a mug, a useful test might be to fill it with hot coffee
one day, and leave it standing for the whole day, or perhaps until the same
time next day, and then have the coffee analyzed for lead and whatever you
suspect might be leached. It would be useful to also test a mugful of
coffee that was freshly brewed, to compare with. Not to make everyone
paranoid, but the coffee itself might contain some undesirables, from the
pipes or from the coffee maker, or from the coffee itself. A geochemical
prospecting analysis company will be able to analyse for a lot of trace
elements in such a liquid sample. The liquid should be sent in a clean,
plastic bottle with a tight top. Best is an unused, sample bottle.
Gavin
Louis H.. Katz on tue 25 apr 00
WOW! I share and office with the same woman. I never see her though she leaves
her cup in front of my computer. I don't wash out the cup because the culture
is her own business, but after looking at my glaze, REDART 60 Calcium
Carbonate 40, I do see a pronounced lack of gloss on the interior and I do
believe it is etching. I may have to really clean the cup to be sure though.
Louis
amy parker wrote:
> ----------------------------Original message----------------------------
> Has anyone considered the extra leaching that might occur with the old
> "office coffee cup"? I had a woman working for me once who never ever used
> soap in her cup - just rinsed it out every day with a quick burst of tap
> water & filled it again... The only time her cup ever got washed was when
> she went out of town for two weeks and the person at the next desk got
> grossed out by the accumulating culture(s).
>
> Amy
> amy parker Lithonia, GA
> amyp@sd-software.com
--
Louis Katz
NEW EMAIL ADDRESS Louis.Katz@mail.tamucc.edu
NCECA Director of Electronic Communication and Webmaster(Ad-Hoc)
Texas A&M-CC Division of Visual and Performing Arts
Visit the NCECA World Ceramics Image Database Online
Looking for a school or a class? Visit NCECA Ceramics Educational Programs
Database Online
Ron Roy on wed 26 apr 00
OK Louis - I'll go bravely.
If this is a cone 6 glaze it's very short of silica and oversupplied with
CaO - I would guess it's a prime canidate for an example of a non durable
glass when in contact with acidic foods.
Good for you to publish this - nothing like a pratical example to get some
attention.
Bests regards, RR
>----------------------------Original message----------------------------
>WOW! I share and office with the same woman. I never see her though she leaves
>her cup in front of my computer. I don't wash out the cup because the culture
>is her own business, but after looking at my glaze, REDART 60 Calcium
>Carbonate 40, I do see a pronounced lack of gloss on the interior and I do
>believe it is etching. I may have to really clean the cup to be sure though.
>Louis
>
>
>amy parker wrote:
>
>> ----------------------------Original message----------------------------
>> Has anyone considered the extra leaching that might occur with the old
>> "office coffee cup"? I had a woman working for me once who never ever used
>> soap in her cup - just rinsed it out every day with a quick burst of tap
>> water & filled it again... The only time her cup ever got washed was when
>> she went out of town for two weeks and the person at the next desk got
>> grossed out by the accumulating culture(s).
>>
>> Amy
>> amy parker Lithonia, GA
>> amyp@sd-software.com
>
>--
>
>Louis Katz
>NEW EMAIL ADDRESS Louis.Katz@mail.tamucc.edu
>NCECA Director of Electronic Communication and Webmaster(Ad-Hoc)
>Texas A&M-CC Division of Visual and Performing Arts
>Visit the NCECA World Ceramics Image Database Online
>Looking for a school or a class? Visit NCECA Ceramics Educational Programs
>Database Online
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
iandol on thu 27 apr 00
------------------
Subject: Re: Leaches
If anything untoward, healthwise, is to occur from using office mugs it may =
be a
good dose of tonsillitis or influenza rather than poisoning from a leaching
glaze. Forty years experience informs me that office mugs or cups were =
rarely
washed to good hygiene standards and the tea cloth which was used to dry =
them
may have been washed sometime, that is, after it has been used to wipe of =
the
grime from the lip of the pot. I believe a good military term for the =
illness
was NAAFI Fever. Flight Sergeants were immune.
Ivor Lewis
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