Robbie Hunsinger on thu 27 mar 97
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Dear Monona, Gavin, Ron, Evan, Tom, Tony, Ric, Linda, Richard, Vince et al-
There seems to be a gap between current thought on safe clayworking =
practices,
and the methods I've seen used at various group studios and classrooms. =
Some
Clayart contributions could help me create change in this area. I know it's=
a
vast topic, but anything in writing might help.
Here are some particular concerns:
What are appropriate materials for kids K-12 to work with? Just clay?
Commercial underglazes? Commercial clear glaze? A boron frit clear glaze?
Metal oxides? Forget the low-fire stuff and stick to high-fire materials? =
Does
anyone have a recipe for a reliable, non-toxic clear low-fire glaze (06-04) =
for
terra cotta (without the boron/iron clouds) that can be brushed or painted =
on?
What is a reasonable age to introduce students to more toxic materials?
College-age?
I understand that the presence of fugitive copper in an electric kiln can
destabilize an otherwise stable commercial lead glaze, inducing it to leach.=
Is
that true? Will an electric kiln build up lead deposits from these =
commercial
glazes and contaminate subsequent fired pieces?
How much copper in a glaze is too much? How much crazing is acceptable in
high-fire functional work? What if there's no barium, lithium, manganese, =
etc.
to leach out, but the glaze is crazed? Is it different for low-fire?
Again, I apologize for the truckload of questions but your reponses to these=
and
any other salient issues you'd like to add could make a difference. Monona,
I've ordered your book, so that will be a help when it comes. =
Thanks,
all.
Ron Roy on sat 29 mar 97
Hi Robbie,
I don't want you to think I am ignoring your post but I need time to think
about it. I do have some comments though.
NO lead - absolutely not. One of the aspects of firing lead is that it will
volatilize and contaminate everything - even if the glaze says food safe
there is no guarantee. ANY reduction (yes it happens in electric kilns - a
lot) will break the lead oxide down into pure lead which boils off starting
at 471C.
It is easier to make glazes at cone 6 so I would say fire above earthenware
temps. You can have better glazes and you can vitrify the clay enough so it
doesn't leak.
Clays at higher temps have better working qualities as well.
You can ask for material data safety sheets in Canada - they have to list
all the ingredients in clays and glazes - I forget what the equivalent name
of those sheets are in the US - where are you?
I don't have much time these days as I am getting ready to go to NCECA.
Post me again about this after April 7 and I will try to be of more help.
Ron Roy
Toronto, Canada
Evenings, call 416 439 2621
Fax, 416 438 7849
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