Sincultura 13 on wed 30 mar 05
Hi everyone, I'm looking for a list of materials that could be safely used in a low fire (cone 04-02) liner glaze that is not going to be lab tested for leaching. I've seen partial lists around the web, so I know that my choice of color is going to be limited... Still, I want to see if I could find a couple more of options other than the white and beige I've been able to come up with or atleast ways to variegate or speckle them safely.
What about using underglazes as coloring for my bases? Would toxic substances leach out of glazes if I use nontoxic commercial underglazes either mixed, under or above?
thanks
Sincultura
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Paul Lewing on wed 30 mar 05
on 3/30/05 3:59 PM, Sincultura 13 at sincultura13@YAHOO.COM wrote:
> What about using underglazes as coloring for my bases? Would toxic substances
> leach out of glazes if I use nontoxic commercial underglazes either mixed,
> under or above?
Keep in mind that there is no clear dividing line between what's an
underglaze and what's a glaze, or what's a clay body, for that matter.
They're all made out of the same set of ingredients, just in different
proportions. Albany slip, for example, could be used as a clay body, at the
right (low) temperature.
Especially when it comes to colors, there are only a few choices, no matter
what material you're coloring. Underglazes, glazes, overglazes, raw oxides,
commercial stains, both body stains and glaze stains- if it's, for instance,
blue, the colorant is going to be cobalt. So any set of ingredients from
which you can make a nontoxic underglaze can also be used to make a nontoxic
glaze, just be varying the proportions.
To be more specific to your question, using underglazes and covering them
with a clear glaze that you know to be nontoxic (and most of them are)
probably will ensure that any bad stuff in the underglaze would not leach
out.
Mixing underglazes with your glaze will drastically alter the character of
the glaze, probably making it much dryer. Underglazes are essentially
colored slips (clay). The only difference between commercial underglazes
and the slips most of us mix up is that they put lots of gum in the
commercial ones so the brush more easily.
Applying underglaze over a glaze is an even worse idea. Imagine brushing a
layer of clay on top of your glaze.
As far as coloring a liner glaze- it's a crap shoot. All of the colorants
are heavy metals. Some we know to be toxic, at least under certain
circumstances or at certain stages in the process. The rest have not been
proven to be harmful, but that may just be because no studies have been
done.
The most cautious course would be to stick with white or clear liner glazes
that you know do not contain lead. That's the only non-colorant that's
really been proven to be toxic. Some people avoid barium and/or lithium,
but there's no hard evidence that either is harmful, it just stands to
reason that they could be.
So the real answer is, it's up to you. Educate yourself, and decide for
yourself.
Paul Lewing, Seattle
sincultura13 on fri 1 apr 05
Many Thanks. Do you have any suggestions of Books with current
information on the matter? I wish there was a Mastering Cone 03
glazes...
thanks again
Sincultura
> The most cautious course would be to stick with white or clear liner
glazes
> that you know do not contain lead. That's the only non-colorant
that's
> really been proven to be toxic. Some people avoid barium and/or
lithium,
> but there's no hard evidence that either is harmful, it just stands to
> reason that they could be.
> So the real answer is, it's up to you. Educate yourself, and decide
for
> yourself.
> Paul Lewing, Seattle
>
Kate Johnson on fri 1 apr 05
> Many Thanks. Do you have any suggestions of Books with current
> information on the matter? I wish there was a Mastering Cone 03
> glazes...
Amen to THAT, Sincultura. Is anyone working on the low fire stuff?
I bought the Potter's Palette and find it fascinating, beautiful, and
helpful, but fairly depressing. The glazes they show for low fire are
either lead-based or crackled/crazed--a problem that is addressed therein,
but not solved.
Best--
Kate Johnson
http://www.cathyjohnson.info/
Art, History, Nature and More at Cathy Johnson's Cafepress--
http://www.cafepress.com/cathy_johnson/
Graphics/Fine Arts Press--
http://www.epsi.net/graphic/
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