Gary and Carla Goldberg on thu 29 jan 04
From what I can tell, there is no way to guarantee that Mason Stains are =
"food safe" unless it is tested by an official lab. So I'm wondering =
how you are using your stains with slip other than making tiles. Are =
you just putting the slip in areas that the user will not touch (ie: =
below the rim on the outside of a mug)? =20
I wanted to use it with slip as a way to color the clay and then cut =
designs into the damp clay, fire, coat with clear food safe glaze, and =
fire again; but I'm learning that is not "food safe." My vision was to =
make large platters with fun designs on them. Are the rest of you just =
putting low fire underglazes on the wet clay instead of "painting" with =
slip? Any ideas out there???? Thanks!
- Carla
Creative Clay Concepts Inc.
http://creativeclay.tripod.com/home.html
John Hesselberth on fri 30 jan 04
On Thursday, January 29, 2004, at 05:06 PM, Gary and Carla Goldberg
wrote:
> I wanted to use it with slip as a way to color the clay and then cut
> designs into the damp clay, fire, coat with clear food safe glaze, and
> fire again; but I'm learning that is not "food safe." My vision was
> to make large platters with fun designs on them. Are the rest of you
> just putting low fire underglazes on the wet clay instead of
> "painting" with slip? Any ideas out there???? Thanks!
Hi Carla,
Putting a good, durable clear glaze on top of a slip or questionable
glaze will cut down very significantly on any leaching that occurs. No
one can say it will cut it to an acceptable level without testing the
final product, but it does help.
Regards,
John
http://www.frogpondpottery.com
http://www.masteringglazes.com
Paul Lewing on sat 31 jan 04
on 1/29/04 2:06 PM, Gary and Carla Goldberg at gone2dog@MTAONLINE.NET wrote:
Carla, some of your conceptions are right on and some are way off. Here
goes:
> From what I can tell, there is no way to guarantee that Mason Stains are =
> "food safe" unless it is tested by an official lab.
You are correct here.
Are you just putting the slip in areas that the user will not touch (ie: =
> below the rim on the outside of a mug)?
No user of any pottery will ever get poisoned by just touching any surface.
Even touching it with their lips, much less their hands.
>
> I wanted to use it with slip as a way to color the clay and then cut =
> designs into the damp clay, fire, coat with clear food safe glaze, and =
> fire again; but I'm learning that is not "food safe."
There is no reason to think that's not OK. Whoever told you that is wrong.
Are the rest of you just =
> putting low fire underglazes on the wet clay instead of "painting" with =
> slip?
Keep in mind that slips and underglazes are essentially the same thing-
colored clay. While it's true that you use a much higher amount of colorant
(which aside from lead and (maybe) barium, are the toxic things) in a slip
than you do in a glaze, we also know that what usually makes a glaze
unstable is that it doesn't have enough alumina and silica. Well, there's
nothing in clay BUT alumina and silica. So I'd surmise that colored clays
would leach less than colored glazes.
Also, keep in mind how stuff is leached. In fact, look at the home test. A
fairly strong acid, like vinegar, sits in the thing for three days. The
likelihood of any one ingesting any amount of harmful stuff off a platter is
miniscule.
Paul Lewing, Seattle
Ron Roy on mon 2 feb 04
Paul said
>No user of any pottery will ever get poisoned by just touching any surface.
>Even touching it with their lips, much less their hands.
It's beside the point Paul - by law here in Canada - you cannot have any
glaze with lead or Cadmium within lip distance from the rim on the outside
- unless the glaze can pass the leach tests - now why would they specify
that?
>> I wanted to use it with slip as a way to color the clay and then cut =
>> designs into the damp clay, fire, coat with clear food safe glaze, and =
>> fire again; but I'm learning that is not "food safe."
>There is no reason to think that's not OK. Whoever told you that is wrong.
Again - if lead or candmium are used they must be lab tested - to see if
the safe glaze is really safe - many glaze makers say their glazes are food
safe because they don't have any lead or cadmium in them - it does not mean
the glazes are stable in many cases - so other toxic oxides may still be
leached out - through the glaze.
> Are the rest of you just =
>> putting low fire underglazes on the wet clay instead of "painting" with =
>> slip?
>Keep in mind that slips and underglazes are essentially the same thing-
>colored clay. While it's true that you use a much higher amount of colorant
>(which aside from lead and (maybe) barium, are the toxic things) in a slip
>than you do in a glaze, we also know that what usually makes a glaze
>unstable is that it doesn't have enough alumina and silica. Well, there's
>nothing in clay BUT alumina and silica. So I'd surmise that colored clays
>would leach less than colored glazes.
Again - one of the conditions for sability is that the glaze be well melted
- in other words - not have too much alumina and silica.
>Also, keep in mind how stuff is leached. In fact, look at the home test. A
>fairly strong acid, like vinegar, sits in the thing for three days. The
>likelihood of any one ingesting any amount of harmful stuff off a platter is
>miniscule.
>Paul Lewing, Seattle
Again - it depends on how long food is left on a platter - maybe fish
overnight in the fridge - there is no way we can imagine how our pots will
be used - the laws are quite clear - if lead and/or cadmium are present and
the pot can hold liquid - and the glaze does not pass a leach test - you
have to put a hole in it or impress the the message that it is not to be
used for food.
RR
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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