Christopher M. Rose on wed 31 mar 99
Hello Clayart,
I am new to the list so 'Hi!' to everybody. (By the way, could someone
tell me
when Clary Illian's book is coming out?)
We have a glaze, being used by students here at the Baltimore Potter's
Guild,
called "JJ's Turquoise". The recipe, as we have it, is
Strontium Carbonate 1200
Neph Sy 2600
Kaolin 280
Flint 320
Lithium Carb 80
Copper Carb 200
Bentonite 80
I sat down to use GlazeChem on my new computer the other night,
with a big Turquoise tumbler full of orange juice, and by the time I
reached the bottom of the glass I'd wished I hadn't. Subsequently
I have tried leaving half-slices of raw orange on a JJ's Turquoise plate
and found them to be bluish a day or two later. It appears to me that
JJ's is leaching copper.
It gets worse. I started comparing strontium-loading recipes and found
that JJ's Turquoise is within a percent or two of Pete's Strontium Matt;
Pete's Strontium Matt
Neph Sy 60
Lithium Carb 1
Strontium Carb 20
Ball Clay 10
Flint 9
Bentonite 2
Turquoise variation - add 5% Copper Carb.
So my concern is that these glazes have been widely distrbuted to
students,
and published - recently even - in magazines, and largely portrayed as
safe, while
a popular variation is very clearly leaching. I will do my orange-slice
trick with
PSM in the next couple of days but expect the results to be roughly the
same.
I guess my questions for the group are;
-What is an acceptable or tolerable amount of copper carbonate leaching?
-What are the real health implications?
-How would one go about getting real testing done for this?
and on a larger and vaguer (more vague?) note, how as a community
should
we address this?
Thanks,
Christopher M. Rose
John Hesselberth on thu 1 apr 99
Hi Christopher,
Welcome to Clayart! Your glaze below may or may not be poisoning anyone,
but it certainly sounds like it is not suitable as a functional glaze.
There are two screening tests many of us use to determine whether a glaze
is even close to being suitable for regular use. First we do a vinegar
soak test for 1-3 days. If there is any change in color in the pot or if
the vinegar is discolored, the glaze is pretty unstable--not the kind of
thing that would hold up to repeated cycles of food and dishwashers. The
second test is to stick it in the back of a dishwasher and leave it there
for 30 or more cycles. Again, if it fades it is not durable enough for
use in functional pieces. If it passes these tests, the next step is to
have it tested professionally somewhere like the Alfred Analytical
Laboratory. I suspect this glaze won't make it that far. However,
instructions for having it tested are posted on my website at
http://www.frogpondpottery.com/glazetest.html There is no established
"safe" level for copper; however you can find discussions of peoples view
in the archives. My own goal is to have it well under 10 mg/l and
preferrably less than 2 mg/l until we know more. From what you describe
I'd bet this is well over 50 mg/l, but only testing can tell.
Copper is notoriously difficult to keep in a glaze. Since you didn't
tell us what you fire to I can only make limited comments on the unity
formula. Assuming you are somewhere in the stoneware range it is quite
low on silica. While this doesn't assure that is will leach it is my
opinion that it is more likely. I certainly would not put this glaze on
functional ware without a whole lot more testing.
Let us know what you learn as you begin to test this glaze more
rigorously. John
Christopher M. Rose wrote:
>----------------------------Original message----------------------------
>
>Hello Clayart,
>
>I am new to the list so 'Hi!' to everybody. (By the way, could someone
>tell me
>when Clary Illian's book is coming out?)
>
>We have a glaze, being used by students here at the Baltimore Potter's
>Guild,
>called "JJ's Turquoise". The recipe, as we have it, is
>
>Strontium Carbonate 1200
>Neph Sy 2600
>Kaolin 280
>Flint 320
>Lithium Carb 80
>Copper Carb 200
>Bentonite 80
>
>I sat down to use GlazeChem on my new computer the other night,
>with a big Turquoise tumbler full of orange juice, and by the time I
>reached the bottom of the glass I'd wished I hadn't. Subsequently
>I have tried leaving half-slices of raw orange on a JJ's Turquoise plate
>
>and found them to be bluish a day or two later. It appears to me that
>JJ's is leaching copper.
>
>It gets worse. I started comparing strontium-loading recipes and found
>that JJ's Turquoise is within a percent or two of Pete's Strontium Matt;
>
>Pete's Strontium Matt
>
>Neph Sy 60
>Lithium Carb 1
>Strontium Carb 20
>Ball Clay 10
>Flint 9
>Bentonite 2
>
>Turquoise variation - add 5% Copper Carb.
>
>So my concern is that these glazes have been widely distrbuted to
>students,
>and published - recently even - in magazines, and largely portrayed as
>safe, while
>a popular variation is very clearly leaching. I will do my orange-slice
>trick with
>PSM in the next couple of days but expect the results to be roughly the
>same.
>
>I guess my questions for the group are;
>
>-What is an acceptable or tolerable amount of copper carbonate leaching?
>
>-What are the real health implications?
>-How would one go about getting real testing done for this?
>
>and on a larger and vaguer (more vague?) note, how as a community
>should
>we address this?
>
>Thanks,
>
>Christopher M. Rose
John Hesselberth
Frog Pond Pottery
P.O. Box 88
Pocopson, PA 19366 USA
EMail: john@frogpondpottery.com web site: http://www.frogpondpottery.com
"It is time for potters to claim their proper field. Pottery in its pure
form relies neither on sculptural additions nor on pictorial decorations.
but on the counterpoint of form, design, colour, texture and the quality
of the material, all directed to a function." Michael Cardew in "Pioneer
Pottery"
Roxana Genis on thu 1 apr 99
Hi
I just returned from a workshop at arrowmont with Clary Illian and she said
her book would be available in May.
Roxana
Monona Rossol on fri 2 apr 99
----------------------
Date: Wed, 31 Mar 1999 13:55:42 EST
From: "Christopher M. Rose"
To: CLAYART@LSV.UKY.EDU
Subject: Glaze leaching concern -
----------------------------Original message----------------------------
Hello Clayart,
SNIP
We have a glaze, being used by students here at the Baltimore Potter's
Guild, called "JJ's Turquoise". The recipe, as we have it, is
Strontium Carbonate 1200
Neph Sy 2600
Kaolin 280
Flint 320
Lithium Carb 80
Copper Carb 200
Bentonite 80
I sat down to use GlazeChem on my new computer the other night,
with a big Turquoise tumbler full of orange juice, and by the time I
reached the bottom of the glass I'd wished I hadn't. Subsequently
I have tried leaving half-slices of raw orange on a JJ's Turquoise plate
and found them to be bluish a day or two later. It appears to me that
JJ's is leaching copper.
It gets worse. I started comparing strontium-loading recipes and found
that JJ's Turquoise is within a percent or two of Pete's Strontium Matt;
Pete's Strontium Matt
Neph Sy 60
Lithium Carb 1
Strontium Carb 20
Ball Clay 10
Flint 9
Bentonite 2
Turquoise variation - add 5% Copper Carb.
So my concern is that these glazes have been widely distrbuted to
students, and published - recently even - in magazines, and largely portrayed
as safe, while a popular variation is very clearly leaching. I will do my
orange-slice trick with PSM in the next couple of days but expect the results
to be roughly the same. I guess my questions for the group are;
-What is an acceptable or tolerable amount of copper carbonate leaching?
-What are the real health implications?
-How would one go about getting real testing done for this?
and on a larger and vaguer (more vague?) note, how as a community
should we address this? Thanks,
Christopher M. Rose
-------------------------------------------------------
I hear this kind of story over and over. And the lab even notices color
changes on some glazes after leaching. As for your questions:
1. The water standard for copper is 1.3 ppm so that's what we'd like to see
on a standard leach test. But what makes you think that the copper is the
only ingredient leaching? All the ingredients are leaching.
2. The health implications: The copper is hazardous to people with Wilson's
Disease. Lithium is colorless and the pot could be a danger to people on
lithium carbonate therapy. At high enough concentrations both substances can
be hazardous to others as well.
3. Where to test: Contact Roland Hale
Alfred Analytical Laboratory
Ceramic Corridor @ Alfred University
200 N Main
Alfred NY 14802 607/478-8074
4. How as a community should we address this?
a) Test several pieces of the ware for copper and lithium to get some idea
of the range of concentrations of these substances to which a person
might be exposed.
b) Provide this information to a consulting toxicologist/MD to write a
short report on the risks to consumers. I know a couple that I might be able
to get to do this reasonably and word things in the best light possible.
c) Provide this report to as many customers as you can contact. You need
to recall the items just as all other companies that make a defective product
have to do. What else can you ethically do? You can't just let your
customers and their children use the ware.
d) Talk to your Guild's lawyer. If you have liability insurance for the
Guild's Board, you could be in good shape. If not, get advice about how
best to protect yourselves.
Monona Rossol
Arts, Crafts and Theater Safety
181 Thompson St., # 23
New York NY 10012-2586 212/777-0062
Ron Roy on mon 5 apr 99
Hi Christopher,
Just ran these two through my calculator - Pete's comes off as a better
glaze - more silica and more alumina - Pete's is higher in alkalies - they
are both high - not a good sign. Both have too much copper and both are
loaded with SrO. I would have to conclude they are both unbalanced glazes,
too matte and too saturated with cooper to be considered good for contact
with food.
I predict they will both change colour given the right circumstances.
How should we address this kind of situation. It is happening right here on
clay art - what we need is a library of glazes that will be acceptable for
contact with food - interesting glazes - now that we are beginning to
understand what is acceptable in terms of durable glazes.
I urge all of you to support John Hesselberth's project - send your glazes
with the recipes to Alfred and have them tested and give the right to
include them in the data base being generated.
RR
>----------------------------Original message----------------------------
>I am new to the list so 'Hi!' to everybody. (By the way, could someone
>tell me
>when Clary Illian's book is coming out?)
>
>We have a glaze, being used by students here at the Baltimore Potter's
>Guild,
>called "JJ's Turquoise". The recipe, as we have it, is
>
>Strontium Carbonate 1200
>Neph Sy 2600
>Kaolin 280
>Flint 320
>Lithium Carb 80
>Copper Carb 200
>Bentonite 80
>
>I sat down to use GlazeChem on my new computer the other night,
>with a big Turquoise tumbler full of orange juice, and by the time I
>reached the bottom of the glass I'd wished I hadn't. Subsequently
>I have tried leaving half-slices of raw orange on a JJ's Turquoise plate
>
>and found them to be bluish a day or two later. It appears to me that
>JJ's is leaching copper.
>
>It gets worse. I started comparing strontium-loading recipes and found
>that JJ's Turquoise is within a percent or two of Pete's Strontium Matt;
>
>Pete's Strontium Matt
>
>Neph Sy 60
>Lithium Carb 1
>Strontium Carb 20
>Ball Clay 10
>Flint 9
>Bentonite 2
>
>Turquoise variation - add 5% Copper Carb.
>
>So my concern is that these glazes have been widely distrbuted to
>students,
>and published - recently even - in magazines, and largely portrayed as
>safe, while
>a popular variation is very clearly leaching. I will do my orange-slice
>trick with
>PSM in the next couple of days but expect the results to be roughly the
>same.
>I guess my questions for the group are;
>-What is an acceptable or tolerable amount of copper carbonate leaching?
>-What are the real health implications?
>-How would one go about getting real testing done for this?
>and on a larger and vaguer (more vague?) note, how as a community
>should
>we address this?
>Christopher M. Rose
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
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