Leslie St.Clair on thu 25 mar 99
Hi everybody. I sent some glazes to Alfred Analytical Laboratory for leach
tests. Here are the results. All the glazes were fired to c 6 electric,
witness cones 6 at 3 o'clock. TEMMOKU GOLD:
Cornwall stone 61; Whiting 8; Gerstley Borate 3; RIO 10; Lithium Carb
5.5; dolomite 7; Flint 5.5. RESULT: lithium detected at 0.48 MG/L.
ANNIE'S TAN:
FLint 90; Potash spar 60; Talc 42; EPK 15; Gerstley 96; Rutile,powdered
6; RIO 15.1; granular manganese 2.5. RESULT: manganese detected
at 0.15 MG/L FLOATING BLUE (yes it's the infamous floating blue)
Neph sy 47.3; Gerstley 27; Silica 20.3; EPK 5.4; RIO 2; Cobalt Oxide
1; Rutile, milled 4; bentonite 1. RESULT: cobalt detected at 0.048 MG/L
I believe that the low detection rates mean that these glazes are food safe.
Does anyone have any comments?
Thanks,
Leslie St. Clair
Ft. Mitchell, Kentucky
John Hesselberth on fri 26 mar 99
Hi Leslie,
Wow, thanks for posting these results. I have looked at all of them and
will give what comments I can.
Temmoku Gold
Since this one contains lithium, I don't really know enough to do
anything but make some observations. First there is no water standard
for lithium that I am aware of and it doesn't even get much mention in
the Handbook on the Toxicology of Metals. However, as you are probably
aware, it has some powerful biological activity and lithium acetate is
used therapeutically as an antimanic. Lithium chloride and citrate are
used as antidepressants--all this according to the Merck Index. I have
no idea what concentrations are effective; however I would certainly get
some advice before putting this one on a food surface. I would hope that
Monona or someone else with knowledge of the biological effects of
lithium would comment on this one.
From a compositional standpoint, only a few authors list a limit for
lithium. Schmitz does and shows it as 0.0 - 0.2 for a glossy cone 3-5
glaze and the same for glossy cone 8-10 glazes. He shows less satin or
mat glazes. This glaze calculates at 0.223 so it may be a little high.
Everything else is well within traditional limit formulas.
What is the surface character of this glaze?
Annie's Tan
I doubt the manganese in this one would be much of a problem. We have
all gotten kind of scared of manganese; however the danger appears to be
from inhaled Mn dust or fumes. Again, I am not aware of any water
standard we might compare to; however manganese appears in foods in
significant concentrations and manganese intake via food has been
estimated to range from 2.1-4.1 mg/day in West Germany to 5.8-12.4 mg/day
in India. Wheat and rice contain a lot of it in their bran. The
recommended daily intake for manganese is 2 mg. Somehow a concentration
of 0.15 mg/l seems pretty innocuous. I can never say anything is food
safe, because the bottom line is that no one knows; however I would use
that glaze on food contact surfaces and eat off of it with no concern at
all.
From a compositional standpoint, though, this one is out of limits low on
alumina and out of limits high on magnesium. I calculate 0.185 for
alumina and 0.46 for magnesium. You might want to check resistance to
bases on this one by sticking it in the back of your dishwasher for a
couple months and see if it changes color or surface character. I'd also
like to know the surface character on this one.
Floating Blue
Ahh, the infamous Floating Blue. We'd probably have to shut down Clayart
for lack of adequate messages if we didn't have this one to talk about.
Again there is no water standard for cobalt. Daily intake in food is
very low. It has been estimated at 0.005-0.045 mg/day. Commercial
brewers used to put it in beer at concentrations up to 1.1 mg/l; although
I think they have stopped now. 0.05 mg/l is the detectable limit in the
tests that Alfred does; therefore with your reading of 0.048 mg/l, there
might be some there and there might not be any. I wouldn't worry about
it.
From a limits standpoint, it depends which set of limits you use. Some
would say Floating Blue is high in both alumina and silica; others would
say it is in limits in everything.
I hope this helps and thanks again for posting this information.
John
Leslie St.Clair wrote:
>----------------------------Original message----------------------------
>Hi everybody. I sent some glazes to Alfred Analytical Laboratory for leach
>tests. Here are the results. All the glazes were fired to c 6 electric,
>witness cones 6 at 3 o'clock. TEMMOKU GOLD:
>Cornwall stone 61; Whiting 8; Gerstley Borate 3; RIO 10; Lithium Carb
>5.5; dolomite 7; Flint 5.5. RESULT: lithium detected at 0.48 MG/L.
>ANNIE'S TAN:
>FLint 90; Potash spar 60; Talc 42; EPK 15; Gerstley 96; Rutile,powdered
>6; RIO 15.1; granular manganese 2.5. RESULT: manganese detected
>at 0.15 MG/L FLOATING BLUE (yes it's the infamous floating blue)
>Neph sy 47.3; Gerstley 27; Silica 20.3; EPK 5.4; RIO 2; Cobalt Oxide
>1; Rutile, milled 4; bentonite 1. RESULT: cobalt detected at 0.048 MG/L
>I believe that the low detection rates mean that these glazes are food safe.
>Does anyone have any comments?
>Thanks,
>Leslie St. Clair
>Ft. Mitchell, Kentucky
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"
zahidi on fri 26 mar 99
Thanks, Leslie, for sharing your research!! You are a kind and conscientious
soul.
Please excuse the fly in the ointment, but I need some education. I also
wonder how many newbies will run out and duplicate these glaze recipes and
say "they were tested, and they're safe."
Doesn't the clay body that the glaze was tested on add an important variable
here? If the exact glaze from the same bucket were used on several different
clay bodies, wouldn't we get several different leach test results? Wouldn't
a dissimilar enough expansion ratio cause these glazes to be NON-food safe?
How far do we take this? If our supplier changes the formulation of the clay
in some minute way, should we be retesting the glazes' leachability? How
much variation in raw material source do we allow? Should I retest these
same glazes on my body? Will they replace swimwear? Sheesh. No wonder I
stopped making food service ware. When they fine us for kiln emissions, I'm
outta here. ;-)
Zee in south LA
-----Original Message-----
From: Leslie St.Clair
To: CLAYART@LSV.UKY.EDU
Date: Thursday, March 25, 1999 6:40 AM
Subject: glaze leach test results, C6glazes
>----------------------------Original message----------------------------
>Hi everybody. I sent some glazes to Alfred Analytical Laboratory for leach
>tests. Here are the results. All the glazes were fired to c 6 electric,
>witness cones 6 at 3 o'clock. TEMMOKU GOLD:
>Cornwall stone 61; Whiting 8; Gerstley Borate 3; RIO 10; Lithium Carb
>5.5; dolomite 7; Flint 5.5. RESULT: lithium detected at 0.48 MG/L.
>ANNIE'S TAN:
>FLint 90; Potash spar 60; Talc 42; EPK 15; Gerstley 96;
Rutile,powdered
>6; RIO 15.1; granular manganese 2.5. RESULT: manganese
detected
>at 0.15 MG/L FLOATING BLUE (yes it's the infamous floating blue)
>Neph sy 47.3; Gerstley 27; Silica 20.3; EPK 5.4; RIO 2; Cobalt
Oxide
>1; Rutile, milled 4; bentonite 1. RESULT: cobalt detected at 0.048
MG/L
>I believe that the low detection rates mean that these glazes are food
safe.
>Does anyone have any comments?
>Thanks,
>Leslie St. Clair
>Ft. Mitchell, Kentucky
Leslie St.Clair on sat 27 mar 99
Hello John. First I want to thank you for making it so easy to contact Alfred
University and encouraging everyone to test glazes. I got the Temmoku Gold
recipe off Clayart and it's a beautiful glaze, a translucent dark brown with
floating gold crystal. The surface at cone 5 is a semi-matte with lots of gold
crystal formation and thus a very textured look and mostly gold color. At cone
6, it is a glossy hard surface with far fewer crystals, so it really has a
floating crystal look. I would love to use this glaze for food surface since
it pools up very nicely, especially in bowls. I would appreciate if anyone
has any information about the danger of lithium leaching at that
concentration. Annie's is a golden tan opaque semi gloss with some
speckling. I've been using it for some time and seen no glaze degradation. It
doesn't craze on any clay I've used it on (standard ceramic's 112, 182, 306,
308 and 266). It cleans up nicely and doesn't stain or scratch. I don't use a
dishwasher, but friends have regularly put Annie's pots in the dishwasher with
no problems. Carol Seidman wrote to me off-list to say that the Annie's
base is the same as the Randy's Red that many people are using. So if anyone
is familiar with the Randy's, the Annie's seems to have a similar surface.
I'll keep posting test results as I get them. And thanks again, John , for
providing all the encouragement and information necessary to get this done.
Leslie St. Clair
Ft. Mitchell, Ky
Edouard Bastarache on sun 28 mar 99
------------------
Hello Leslie,
Quebec's standard for manganese in drinking water is 0.05 mg/liter,
there is none for lithium and cobalt.
The average dietary intake of manganese is about 2.0 to 8.8 mg./day,
according to the WHO (World Health Organization,1973),it is an esssential
mineral, you need to have some in your diet.So, if you drink 2 liters of
water
from a mug glazed with your mangenese glaze, you only add 0.30 mg to what
you already get from your diet=3B forget about it.
As for lithium the story is slightly different, the toxic and therapeutic
blood levels are
very close=3B any activity leading to loosing much body water may switch a
patient
taking lithium carbonate form the therapeutic to the toxic zone, as in
sweating in
the melting departments of a steel mills.Also many anti-inflammatory
drugs raise the lithium blood levels of patients and cause the intoxication,
i saw
one case 2 years ago.Motrin(Advil) is one of the possible offenders, it is
important to
remember this name because it may be sold without a prescription.So, as far
as i
am concerned, i am much more afraid of these situations than picking up a
few atoms
of lithium from a pot covered by a lithium-containing glaze=3B more =
specially
if the amount
used is low, the formula is well balanced and the pots are high-fired.
As for cobalt,one atom of it comprises the central and necessary core in the
vitamin B12,
an esssential vitamin for humans.According to =22Dangerous Properties of
Industrial Materials=22
(Richard Lewis) it has a low toxicity by ingestion.According to Sorbie in
1971 only 18=25 of
ingested radioactive cobalt chloride. was absorbed by the gastro-intestinal
tract.So, dont
worry about your cobalt glaze being toxic.
Later,
Edouard Bastarache
edouardb=40sorel-tracy.qc.ca
http://www.sorel-tracy.qc.ca/=7Eedouardb/
-----Message d'origine-----
De : Leslie St.Clair =3CLESAINT1=40aol.com=3E
=C0 : CLAYART=40LSV.UKY.EDU =3CCLAYART=40LSV.UKY.EDU=3E
Date : 25 mars, 1999 07:34
Objet : glaze leach test results, C6glazes
=3E----------------------------Original message----------------------------
=3EHi everybody. I sent some glazes to Alfred Analytical Laboratory for =
leach
=3Etests. Here are the results. All the glazes were fired to c 6 electric,
=3Ewitness cones 6 at 3 o'clock. TEMMOKU GOLD:
=3ECornwall stone 61=3B Whiting 8=3B Gerstley Borate 3=3B RIO 10=3B =
Lithium Carb
=3E5.5=3B dolomite 7=3B Flint 5.5. RESULT: lithium detected at 0.48 =
MG/L.
=3EANNIE'S TAN:
=3EFLint 90=3B Potash spar 60=3B Talc 42=3B EPK 15=3B Gerstley 96=3B
Rutile,powdered
=3E6=3B RIO 15.1=3B granular manganese 2.5. RESULT: manganese
detected
=3Eat 0.15 MG/L FLOATING BLUE (yes it's the infamous floating blue)
=3ENeph sy 47.3=3B Gerstley 27=3B Silica 20.3=3B EPK 5.4=3B RIO 2=3B =
Cobalt
Oxide
=3E1=3B Rutile, milled 4=3B bentonite 1. RESULT: cobalt detected at =
0.048
MG/L
=3EI believe that the low detection rates mean that these glazes are food
safe.
=3EDoes anyone have any comments?
=3EThanks,
=3ELeslie St. Clair
=3EFt. Mitchell, Kentucky
Ron Roy on sun 4 apr 99
Hi Leslie,
I finally had enough time to go over the glazes you had tested. I agree
with Johns comments but would like to add my thoughts re the Tenmoku gold
which gave up so much lithium.
I believe part of the problem with this glaze is the lithium carbonate. If
you would be willing to try some variations and have them tested I would be
willing to revise the glaze and try to make it more durable. I need to know
what feldspar you have (G200 or Custer.)
I also need to have some idea about surface and viscosity - and is it
crazing on your clay.
R.
>----------------------------Original message----------------------------
>Hi everybody. I sent some glazes to Alfred Analytical Laboratory for leach
>tests. Here are the results. All the glazes were fired to c 6 electric,
>witness cones 6 at 3 o'clock. TEMMOKU GOLD:
>Cornwall stone 61; Whiting 8; Gerstley Borate 3; RIO 10; Lithium Carb
>5.5; dolomite 7; Flint 5.5. RESULT: lithium detected at 0.48 MG/L.
>ANNIE'S TAN:
>FLint 90; Potash spar 60; Talc 42; EPK 15; Gerstley 96; Rutile,powdered
>6; RIO 15.1; granular manganese 2.5. RESULT: manganese detected
>at 0.15 MG/L FLOATING BLUE (yes it's the infamous floating blue)
>Neph sy 47.3; Gerstley 27; Silica 20.3; EPK 5.4; RIO 2; Cobalt Oxide
>1; Rutile, milled 4; bentonite 1. RESULT: cobalt detected at 0.048 MG/L
>I believe that the low detection rates mean that these glazes are food safe.
>Does anyone have any comments?
>Thanks,
>Leslie St. Clair
>Ft. Mitchell, Kentucky
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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