Lisa or Ginny on sun 20 apr 97
Ron, Tony, et al.:
I have found the following recipe in Chappell's book for ^6 copper red:
Lead bisilicate 23.6
Whiting 5.5
Kaolin 2.8
Silica 29.4
Borax 29.9
Boric Acid 4.5
Sodium Carbonate 4.4
Tin ox 1.6
Copper ox .5
Bentonite 1
RIO .2
CMC 1 tsp.
Next, I read in Rhodes' book that lead glazes with copper oxide are
ESPECIALLY prone to leaching. Here are my questions:
1. Since one of the purposes in fritting is to render the toxic
non-toxic, one would assume that lead frit is therefore non-toxic. Would
that assumption be correct?
2. Assuming that said frit is nontoxic, does the copper oxide change
that?
3. Can you reformulate this glaze or suggest other ^6 redux glazes for
copper red?
Thank you muchly!
--
Lisa Skeen
Living Tree Pottery
Greensboro, NC
YesIAmRU?
Email: lpskeen@nr.infi.net
Karen Gringhuis on mon 21 apr 97
Lisa - Go to the library & dig out the article in CERAMICS MONTHLY
June/July/Aug. 1993 by Val Cushing "Get the Lead out."
Read it & save it and ditch this glaze particularly if your
work if functional.
Karen Gringhuis
Tony Hansen on mon 21 apr 97
Lisa or Ginny wrote:
> I have found the following recipe in Chappell's book for ^6 copper red:
> Lead bisilicate 23.6
> Whiting 5.5
....
> 1. Since one of the purposes in fritting is to render the toxic
> non-toxic, one would assume that lead frit is therefore non-toxic. Would
> that assumption be correct?
Don't assume that my reply means I think I fit the subject. The more I
read
on clayart the less I think I know! I miss the good old days of thinking
I knew it all and having no one to tell me how dumb I was.
Lead frits are somewhat safer than raw lead but still soluble.
The final fired glaze does not know whether it got the PbO from lead
oxide
or lead frit. If its formulation is not right the lead will leach.
--
Tony Hansen, IMC
Ron Roy on mon 21 apr 97
Hi Lisa,
Lisa asked -
>I have found the following recipe in Chappell's book for ^6 copper red:
>
>Lead bisilicate 23.6
>Whiting 5.5
>Kaolin 2.8
>Silica 29.4
>Borax 29.9
>Boric Acid 4.5
>Sodium Carbonate 4.4
>Tin ox 1.6
>Copper ox .5
>Bentonite 1
>RIO .2
>CMC 1 tsp.
>
>Next, I read in Rhodes' book that lead glazes with copper oxide are
>ESPECIALLY prone to leaching. Here are my questions:
>
>1. Since one of the purposes in fritting is to render the toxic
>non-toxic, one would assume that lead frit is therefore non-toxic. Would
>that assumption be correct?
Wrong! Even if the lead frit was not toxic the glaze would be something
else and may be.
>2. Assuming that said frit is nontoxic, does the copper oxide change
>that?
There is not much copper so that effect will not be much - as I said I
don't work on lead glazes so I don't even know if the glaze is well
formulated.
>3. Can you reformulate this glaze or suggest other ^6 redux glazes for
>copper red?
I can't - don't work on lead glazes so have no experience - it would be a
completely different glaze without the lead.
Lead is not recommended for cone 6 and above because it really starts to
volitize at that temperature. This case is even worse. Lead oxide is easily
reduced to the metal which boils about 400C. This means the lead (from any
source) will glaze the inside of your kiln, contaminate all the other pots
in the kiln, the shelves, posts and the atmospher - your kiln room, studio
and you. Why anyone would publish a glaze like that - knowing what we know
about lead is beyond my understanding. It certainly makes me wonder about
the other glazes in that book.
Ron Roy
Toronto, Canada
Evenings, call 416 439 2621
Fax, 416 438 7849
ronroy@astral.magic.ca
Janet Capetty on mon 21 apr 97
I'm no glaze guru, but I was excited to see that recipe too in Chappell's
book. When I went to my clay supplier (Great Lakes Clay) they said they
would not sell me lead bisilicate. Although it is supposedly fritted, they
said it was not safe. To prove it to me, they called a Ceramic Chemist and
had him convinceme not to use it.
I'd love to seesomeone's reformulation of that glaze too. Good luck!
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