Paul Lewing on tue 28 feb 12
On Feb 28, 2012, at 4:48 PM, Barbara Francis wrote:
We have recently started using a glaze called Weathered Bronze, that I
understand is not food safe. When a glaze it not food safe, I'm
thinking it's still all right to use in on the outside of a cup.
True. Although not only is it not food-safe (whatever that means-
there's not really a real definition) it is also very unstable. With
use, especially in the dishwasher, it can fade, which will not make
your customers happy.
What about the lip of a cup. Would there still be a danger from
putting your lip against the glaze, or does the leaching only occur
when the liquid or food is sitting next to the glaze.
Touching it with your lip would not hurt you. To leach, it needs an
acid environment, and it needs to sit a while. Saliva is almost
exactly pH neutral and you only touch the lip for a few seconds.
What about using a bowl just for a dry food? Would that be okay?
Yes, but you have no control over what your customers do with your bowl.
Paul Lewing
www.paullewingtile.com
www.paullewingart.com
Barbara Francis on tue 28 feb 12
Hi All=3D0A=3DA0=3D0AWe have recently started using a glaze called Weathere=
d Bron=3D
ze, that I understand is not food safe.=3DA0 When a glaze it not food safe,=
I=3D
'm thinking it's still all right to use in on the outside of a cup.=3DA0 Wh=
at=3D
about the lip of a cup.=3DA0 Would there still be a danger from putting yo=
ur=3D
lip against the glaze, or does the leaching only occur when the liquid or =
=3D
food is sitting next to the glaze.=3DA0 What about using a bowl just for a =
dr=3D
y food?=3DA0 Would that be okay? =3D0A=3DA0=3D0AMany thanks, Barb Francis
John Hesselberth on wed 29 feb 12
Hi Barb,
First let me say I am glad you are concerning yourself with issues like =3D
this. More and more potters are.
That said, Weathered Bronze Green (a Pete Pinnell glaze) is actually =3D
pretty stable if fired to a full cone 6 and if no one has sneaked more =3D
copper into it than the original recipe called for. I still wouldn't =3D
personally put it on food surfaces, but I see no problem with it on the =3D
outside of functional work and, perhaps, even on the lip. But its =3D
stability deteriorates rapidly if not fired to a full cone 6--it was =3D
originally developed as a cone 9 glaze if memory serves me.
My testing of the glaze is summarized here: =3D
http://frogpondpottery.com/glazestability/glaze0022.html
So if this is in a community studio where kiln conditions are not well =3D
controlled or the kiln has a cold shelf or two or a less careful potter =3D
gets hold of the glaze and puts it on the inside of a mug, I would =3D
recommend you not use it on functional work. But if you have a carefully =
=3D
controlled situation, go for it.=3D20
The question might be more one of durability in use rather than safety. =3D
Put a mug glazed with it in your dishwasher for a couple months. Compare =
=3D
it to a brand new mug and look for fading. Also fill a cup or mug (that =3D
is glazed on the inside with WBG) with regular household vinegar and let =
=3D
it set for 3 days. Carefully empty it, wash it, and thoroughly dry it. =3D
Then look for fading or sheen changes on the surface. If it passes both =
=3D
of those tests your control of your kiln is probably fine.
Regards,
John
On Feb 28, 2012, at 7:48 PM, Barbara Francis wrote:
> Hi All
> =3D20
> We have recently started using a glaze called Weathered Bronze, that I =
=3D
understand is not food safe. When a glaze it not food safe, I'm =3D
thinking it's still all right to use in on the outside of a cup. What =3D
about the lip of a cup. Would there still be a danger from putting your =
=3D
lip against the glaze, or does the leaching only occur when the liquid =3D
or food is sitting next to the glaze. What about using a bowl just for =3D
a dry food? Would that be okay?=3D20
> =3D20
> Many thanks, Barb Francis
The dumbest people I know are those that know it all. Malcolm Forbes
John Hesselberth
john@frogpondpottery.com
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