Chi1558090944@AOL.COM on fri 21 feb 03
If you paint cobalt oxide over a food safe glaze, is the glaze still food
safe?
thanks,
M
Vince Pitelka on sat 22 feb 03
> If you paint cobalt oxide over a food safe glaze, is the glaze still food
> safe?
M -
If you use cobalt oxide, you can paint it under the glaze, and it will not
crawl. And it also will not smear while you are loading the kiln.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Office - wpitelka@tntech.edu
615/597-6801 x111, FAX 615/597-6803
http://iweb.tntech.edu/wpitelka/
Ron Roy on tue 25 feb 03
Hi M
No way - if you even overload any glaze with enough colouring oxides it
will start leaching - best to take the suggestion of putting it under the
glaze.
A better way is to mix the cobalt with the glaze - in the ratio that gives
you the colour you want and put it over - or even better - under.
There is a potential problem here - cobalt is a strong flux at cone 6 and
will tend to bleed unless the glaze is quite stiff.
Now I am thinking - is it just a wash - a very thin watery solution - and
only on the out side - maybe that would be OK - especially if combined with
a good stable glaze (read high in SiO2 and Al2O3.)
RR
>If you paint cobalt oxide over a food safe glaze, is the glaze still food
>safe?
>
>thanks,
>M
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
John Baymore on fri 28 feb 03
Paul,
It seems to me that if the glaze and colorants in question contain no
toxic materials like copper, barium, etc., then it would still be "food
safe". Is cobalt a material of potential concern? I thought it was one
of the non-toxic colorants. Or is it only safe when used in small
amounts, like 1% or less?
Take a look at the MSDS and other toxicology references for cobalt
compounds. Somehow potters seem to think cobalt is akin to something lik=
e
maybe iron. It isn't.
Even iron ain't completely a non-issue. Monona Rossol even has a
documented case of iron poisoning from an iron saturate glazed coffee mug=
with an overspray of iron oxide which was used daily....... by a
lawyer.............. if I remember correctly.
There is no exact definition of what is meant by "food safe". It is sort=
of like "handcrafted" . There are only FDA leaching standards for le=
ad
and cadmium. =
Best,
..............................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752 (s)
800-900-1110 (s)
JohnBaymore.com
JBaymore@compuserve.com
"DATES SET: Earth, Water, and Fire Noborigama Woodfiring Workshop
August 15 - 24, 2003"
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