"Terry Sullivan/Nottingham Center for the Arts. San Marcos," on tue 3 nov 98
Hi all,
I need some assistance from you glaze doctors and toxic materials folks.
An old friend, who has been a studio potter for 12 years, uses a glaze on
functional ware that I'm sure is not safe. In addition; he mixes and applies
the glaze without any protection for skin or breathing. He will sometimes
listen to me but is somewhat stubborn and slow to change (he's mostly self
taught and has quite a few large gaps in his ceramic education, especially
in the tech area).
I figure that if he gets it from other more knowlegeable ceramists then he
will at least moderate or quit some of his more dangerous practices.
Specificly this glaze mentioned above:
Barium carb 22.8 %
Calcium carb 9.78 %
G-200 spar 56.5 %
OM 4 ( ball cly) 10.88%
add:
Zinc oxide 6 %
Copper carb 4.2 %
Rutile 4.25 %
This is fired to cone 10 oxidation in updraft natural gas on Ardvark "navajo"
( a porcelaneous sanded white stoneware) and produces a satin/mat.
green/turquoise glaze (similar to the old TECO ware).
In addition to the toxicity issue; this glaze tends to pinhole and will run if
pushed to a "hard" 10. It seems to pinhole less if applied on porcelain slip.
Very much appriciate your help on both problems.
Terry Sullivan
Nottingham Center for the Arts
personal email to: Go2tms@aol.com or
tsullivan@nottinghamarts.org
Ron Roy on tue 10 nov 98
Hi Terry,
This glaze is seriously short of silica at cone 10 and probably crazing -
which makes the situation even worse. It will release BaO ions into food in
many situations - way more than any water standard for what I have seen and
read - it will change colour under some conditions - take a cup or bowl
with this glaze onthe inside and leave some vinegar in it for 24 hours at
room temp - I think you will see some changes.
RR
>----------------------------Original message----------------------------
>Hi all,
>I need some assistance from you glaze doctors and toxic materials folks.
>
>An old friend, who has been a studio potter for 12 years, uses a glaze on
>functional ware that I'm sure is not safe. In addition; he mixes and applies
>the glaze without any protection for skin or breathing. He will sometimes
>listen to me but is somewhat stubborn and slow to change (he's mostly self
>taught and has quite a few large gaps in his ceramic education, especially
>in the tech area).
>
>I figure that if he gets it from other more knowlegeable ceramists then he
>will at least moderate or quit some of his more dangerous practices.
>
>Specificly this glaze mentioned above:
>
>Barium carb 22.8 %
>Calcium carb 9.78 %
>G-200 spar 56.5 %
>OM 4 ( ball cly) 10.88%
>
>add:
>
>Zinc oxide 6 %
>Copper carb 4.2 %
>Rutile 4.25 %
>
>This is fired to cone 10 oxidation in updraft natural gas on Ardvark "navajo"
>( a porcelaneous sanded white stoneware) and produces a satin/mat.
>green/turquoise glaze (similar to the old TECO ware).
>In addition to the toxicity issue; this glaze tends to pinhole and will run if
>pushed to a "hard" 10. It seems to pinhole less if applied on porcelain slip.
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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