Peter Atwood on sun 16 apr 00
Hi All,
Sometimes I think we potters get a little carried away with this issue of
food safety. As John Hesselberth pointed out in a recent posting, the amount
of copper actually leached
from a glaze he was testing was very small when exposed to a normal
concentration of acid. That is, the usual leaching test done in the lab was
far more severe than what the glaze would be exposed in actual life. Also,
the duration of exposure is generally far less than the duration of the lab
test.
I don't know if barium would follow the model above but I suspect it might.
That might be another direction for the lab testers to follow if they ever
get the chance.
That brings me to another stupid question: If a glaze is tested and found to
leach x number of mg/l of a compound isn't it unlikely that the glaze will
continue to leach the exact same amount upon subsequent occasions? After
all, there is less and less metal available after each leaching. So it would
follow that there would be diminishing returns.
As far as the aluminum controversy is concerned I think it is total RUBBISH
and I think anyone who would cause potters to worry about such nonsense
should have a heart. Potting is a tough enough way to make a living without
needlessly scaring them.
Peter Atwood
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Edouard Bastarache on mon 17 apr 00
Hello Peter,
I agree 100% withn your statement!!!
Later,
Edouard Bastarache
Dans / In "La Belle Province"
edouardb@sorel-tracy.qc.ca
http://www.sorel-tracy.qc.ca/~edouardb/
As far as the aluminum controversy is concerned I think it is total RUBBISH
and I think anyone who would cause potters to worry about such nonsense
should have a heart. Potting is a tough enough way to make a living without
needlessly scaring them.
Peter Atwood
______________________________________________________
Get Your Private, Free Email at http://www.hotmail.com
John Hesselberth on mon 17 apr 00
Peter Atwood wrote:
>
>That brings me to another stupid question: If a glaze is tested and found to
>leach x number of mg/l of a compound isn't it unlikely that the glaze will
>continue to leach the exact same amount upon subsequent occasions? After
>all, there is less and less metal available after each leaching. So it would
>follow that there would be diminishing returns.
Hi Peter,
Not stupid at all. I thought that might be the case too at one
point--still think it could be. The one place where your proposal
probably does happen is in those glazes that are so grossly unstable that
the color changes with a day or two soaking in vinegar. Clearly the
total glaze structure has not dissolved, but the colorants have been
preferentially leached out in that kind of situation. I think the jury is
still out for reasonably stable glazes. I am still hoping that the
leaching is just a "surface" phenomena; although very limited testing
doesn't give me the data I need to show that. I have tested the same mug
twice and one three times and the leaching results were virtually
identical time to time. That would argue that it is not just a leaching
out or dissolving of the "loose" stuff near the surface. Rather, it might
be the entire glaze structure is gradually dissolving in the acid. On the
other hand, I have occasionally tested for other things like boron, along
with copper, and the boron doesn't leach out in proporation to its
concentration. Seems like it should if the total glaze structure were
dissolving. I guess I'd have to run that test another couple dozen times
to be sure though. Actually, per the calculations below I guess I ought
to do it a couple hundred times--ouch, that would be an expensive
experiment. I'll have to think of a cheaper way to get at that answer.
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.
Your thought is a good provocation though. It caused me to think this
whole issue through again. I'll try to figure out an affordable way to
prove it one way or the other.. Thanks.
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.
Janet Kaiser on tue 18 apr 00
I agree 100% too, but not being an active potter my opinion (humble or
otherwise) does not count.
However, the whole thread reminds me of the time fresh orange and tomato
juice was introduced frozen, in tetra packs and in bottles. Up to then it
had only been available in tins ("cans" in the colonies). The manufacturers'
could not understand why people tried any or all three of these new
packages, but did not buy a second time...
Why? Because they did not like the taste... No tin taste any more! Just
natural juice!
So, tin was reputedly **added** to the juice for some time, until people got
used to the packaging!!! Then is was slowly reduced... At least that is what
we were told in the UK where the doctored juice with tin additive was not
popular, because we had had no tinned juice in the first place!
Enough to curl some toes on this list... Makes leaching from pots a somewhat
academic mute point methinks....
Janet Kaiser - who likes fresh pressed orange, especially in gin.
The Chapel of Art, Criccieth LL52 0EA, GB-Wales
Home of The International Potters Path
TEL: (01766) 523570
WEB: http://www.the-coa.org.uk
EMAIL: postbox@the-coa.org.uk
----- Original Message ----- >
> I agree 100% withn your statement!!!
> Later,
> Edouard Bastarache
>
> As far as the aluminum controversy is concerned I think it is total
RUBBISH
> and I think anyone who would cause potters to worry about such nonsense
> should have a heart. Potting is a tough enough way to make a living
without
> needlessly scaring them.
> Peter Atwood
Linda Hamm on tue 18 apr 00
Actually, per the calculations below I guess I ought
to do it a couple hundred times--ouch, that would be an expensive
experiment. I'll have to think of a cheaper way to get at that answer.
John
Would it be less expensive if you just did the leachings and only tested a
few for results. Maybe one in 20 or 40. You may get enough information to
create a graph.
Just a thought.
Bob Hamm
Super Mud Works
Kelowna, BC Canada
Ph 250 765-8876
Email hamm@direct.ca
Earl Brunner on wed 19 apr 00
That's right in there with processed peas. yuck! I grew up
on fresh
frozen (hows that for an oxymoron?)peas. The first time I
was served
processed peas in England I thought I'd die. Funny how we
see things
from our own culture. I knew a lady in England that took
her package
of paper plates back to the shop where she had purchased
them and wanted
a refund. They had only lasted through three washings. We
Americans have
such a throw-away society.
Janet Kaiser wrote:
>
> ----------------------------Original message----------------------------
> I agree 100% too, but not being an active potter my opinion (humble or
> otherwise) does not count.
>
> However, the whole thread reminds me of the time fresh orange and tomato
> juice was introduced frozen, in tetra packs and in bottles. Up to then it
> had only been available in tins ("cans" in the colonies). The manufacturers'
> could not understand why people tried any or all three of these new
> packages, but did not buy a second time...
>
> Why? Because they did not like the taste... No tin taste any more! Just
> natural juice!
>
> So, tin was reputedly **added** to the juice for some time, until people got
> used to the packaging!!! Then is was slowly reduced... At least that is what
> we were told in the UK where the doctored juice with tin additive was not
> popular, because we had had no tinned juice in the first place!
>
> Enough to curl some toes on this list... Makes leaching from pots a somewhat
> academic mute point methinks....
>
> Janet Kaiser - who likes fresh pressed orange, especially in gin.
> The Chapel of Art, Criccieth LL52 0EA, GB-Wales
> Home of The International Potters Path
> TEL: (01766) 523570
> WEB: http://www.the-coa.org.uk
> EMAIL: postbox@the-coa.org.uk
> ----- Original Message ----- >
> > I agree 100% withn your statement!!!
> > Later,
> > Edouard Bastarache
> >
> > As far as the aluminum controversy is concerned I think it is total
> RUBBISH
> > and I think anyone who would cause potters to worry about such nonsense
> > should have a heart. Potting is a tough enough way to make a living
> without
> > needlessly scaring them.
> > Peter Atwood
--
Earl Brunner
http://coyote.accessnv.com/bruec
mailto:bruec@anv.net
John Hesselberth on wed 19 apr 00
Linda Hamm wrote:
>----------------------------Original message----------------------------
>
> Actually, per the calculations below I guess I ought
>to do it a couple hundred times--ouch, that would be an expensive
>experiment. I'll have to think of a cheaper way to get at that answer.
>
>John
>
>Would it be less expensive if you just did the leachings and only tested a
>few for results. Maybe one in 20 or 40. You may get enough information to
>create a graph.
>
>Just a thought.
>
>Bob Hamm
>Super Mud Works
>Kelowna, BC Canada
>Ph 250 765-8876
>Email hamm@direct.ca
Hi Bob,
You are right! You and Gavin Stairs and probably a thousand other
Clayarters saw that before I did. The test pots are in the kiln right
now. Thanks!
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.
Sondra Karipides on fri 21 apr 00
Hi John - -
you wrote
"That would argue that it is not just a leaching
out or dissolving of the "loose" stuff near the surface. Rather, it might
be the entire glaze structure is gradually dissolving in the acid. On the
other hand, I have occasionally tested for other things like boron, along
with copper, and the boron doesn't leach out in proporation to its
concentration. Seems like it should if the total glaze structure were
dissolving. I guess I'd have to run that test another couple dozen times
to be sure though. Actually, per the calculations below I guess I ought
to do it a couple hundred times--ouch, that would be an expensive
experiment. I'll have to think of a cheaper way to get at that answer."
If you want to find out if the copper or any element continues to
leach out after many exposures without the expense and trouble of all
those analyses, I think you'd get the answer by doing many acid
extractions, but only analyzing the first and last. Does this make
sense to you?
Sondra
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