Paul Lewing on mon 2 aug 04
on 8/2/04 1:38 PM, Martin Rice at martinrice1@MAC.COM wrote:
> almost every one calls for lead bisilicate, not something that I want to
> use. Can anyone suggest a substitute for this?
Unfortunately, lead bisilicate is one of the forms of fritted lead, and as
such, is itself the safer substitute for the raw forms of lead oxide.
Bristol glazes, which use zinc instead of lead, were developed for just this
purpose. Sodium melts at an even lower temperature than lead, but its
coefficient of expansion is so high that high-sodium glazes craze like mad.
And many people have tried, and are still trying, to develop boron-based
glazes to replace the lead ones, particularly in the third world. However,
they are facing great resistance from the potters, because the potters know
that nothing even remotely approaches a lead glaze when it comes to
brilliance of color, wide firing range, and ability to fit almost any clay
body. People have been trying for about 150 years to duplicate the effects
of lead glazes, but the substitutes just don't have the "juice".
Below about cone 1, lead is the perfect glaze ingredient.... except for this
one little annoying toxicity drawback.
However, it may not be as bad as you think. Fritted lead, like the
bisilicate, does not volatilize at low-fire temperatures, so there is not
that danger to your customers, which means that if you use a lead-free liner
glaze, you can use them on the outsides of your pots. Of course, all the
dangers to you from dust, etc. still remain.
Paul Lewing, Seattle
pdp1@EARTHLINK.NET on mon 2 aug 04
Hi Paul, all...
What of Tin, Antimony, or Bismuth, in various forms?
How are they for the qualities we seek in Glazes?
Phil
el ve
----- Original Message -----
From: "Paul Lewing"
> on 8/2/04 1:38 PM, Martin Rice at martinrice1@MAC.COM
wrote:
>
> > almost every one calls for lead bisilicate, not
something that I want to
> > use. Can anyone suggest a substitute for this?
>
> Unfortunately, lead bisilicate is one of the forms of
fritted lead, and as
> such, is itself the safer substitute for the raw forms of
lead oxide.
>
> Bristol glazes, which use zinc instead of lead, were
developed for just this
> purpose. Sodium melts at an even lower temperature than
lead, but its
> coefficient of expansion is so high that high-sodium
glazes craze like mad.
> And many people have tried, and are still trying, to
develop boron-based
> glazes to replace the lead ones, particularly in the third
world. However,
> they are facing great resistance from the potters, because
the potters know
> that nothing even remotely approaches a lead glaze when it
comes to
> brilliance of color, wide firing range, and ability to fit
almost any clay
> body. People have been trying for about 150 years to
duplicate the effects
> of lead glazes, but the substitutes just don't have the
"juice".
> Below about cone 1, lead is the perfect glaze
ingredient.... except for this
> one little annoying toxicity drawback.
> However, it may not be as bad as you think. Fritted lead,
like the
> bisilicate, does not volatilize at low-fire temperatures,
so there is not
> that danger to your customers, which means that if you use
a lead-free liner
> glaze, you can use them on the outsides of your pots. Of
course, all the
> dangers to you from dust, etc. still remain.
> Paul Lewing, Seattle
>
>
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Martin Rice on mon 2 aug 04
I have lots of low-fire glaze recipes in my copy of Stephen Murfitt's "The
Glaze Book." Many of them are extremely attractive. Unfortunately, however,
almost every one calls for lead bisilicate, not something that I want to
use. Also saw Lily's warning about it in the archives. Can anyone suggest a
substitute for this?
Thanks,
Martin
Santiago de Puriscal, Costa Rica
Ivor and Olive Lewis on tue 3 aug 04
Dear Martin Rice,
I doubt if anyone has ever bothered to do the reassert which would
give the answers you are calling for.
Regardless of the opinions of those (and I am one of them) who would
not use Lead Bisilicate or similar fluxing materials there is nothing
wrong with glazes using this material if they are correctly compounded
and the ware on which they are employed is tested as acceptable by an
accredited laboratory. Each day millions of people feed off and imbibe
from industrial products which are treated thus.
But it is your choice not to use this material, a choice which I
respect. I like the brilliance of Lead Glazes. But they are useless on
Cone 8 Clay for reasons already discussed in previous years on
Clayart. I solved my problem by going to the Sodium Ion as the flux of
choice. I can get brilliant transparent glazes which mimic those
qualities so esteemed in Lead glazes, but without any of the health
hazards.
You may have to get back to First Principles of Glaze Design: Define
the qualities you are intending to achieve; Select materials which
will allow you to achieve those qualities; Run a series of graded
sample tests to determine which of the potential samples will give you
what you. So you start with one of compounds containing a high
proportion of Silica as your principle glass former. Then select a
material which will give you the highest fraction of Sodium ions
possible but limit fraction of other group one ions. Now consider
adjunct melting fluxes to bring the maturity temperature down. Finally
you may have to include additional pure silica to ensure there is
sufficient to give you a good glass.
Only one problem now, You will not get the typical rich colour
responses associated with Traditional Lead Glazes. Oh yes, I forgot to
say, you may need to make your own frits to accomplish your task.
Well, we all have to make sacrifices.
Have fun with your research.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
----- Original Message -----
From: "Martin Rice"
To:
Sent: Tuesday, 3 August 2004 7:08
Subject: Lead bisilicate substitute?
> I have lots of low-fire glaze recipes in my copy of Stephen
Murfitt's "The
> Glaze Book." Many of them are extremely attractive. Unfortunately,
however,
> almost every one calls for lead bisilicate, not something that I
want to
> use. Also saw Lily's warning about it in the archives. Can anyone
suggest a
> substitute for this?
>
> Thanks,
> Martin
> Santiago de Puriscal, Costa Rica
>
>
______________________________________________________________________
________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your
subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
Paul Lewing on tue 3 aug 04
on 8/2/04 9:07 PM, pdp1@EARTHLINK.NET at pdp1@EARTHLINK.NET wrote:
> What of Tin, Antimony, or Bismuth, in various forms?
How are they for the qualities we seek in Glazes?
As lead substitutes, not good. Lead is a flux. Tin is an opacifier;
antimony is a colorant. Bismuth is a flux, but I know very little about it,
except that it's expensive. Another of lead's advantages is that it's
incredibly cheap and abundant. As I say, it's the perfect lowfire glaze
base, except........
Paul Lewing, Seattle
pdp1@EARTHLINK.NET on wed 4 aug 04
Hi Paul,
Oh well...
I do not know much about all that and was just curious.
The Glazes I used and did have some experience with, were
made of Ashes (seived and washed usually, from my Wood
Stove, ) and old Mine tailings
( fine like Powdered-sugar, sitting since 1916 or
or earlier maybe, from abandonded Mines, near Nelson,
Nevada...)
and or some some local Clay with or without some
concentrated rust Water...
They were allways ^10 and behaved well...no problems as I
recall from fit or finish. I got lucky right off the bat and
was happy...
The 'school' glazes did not appeal to me and I avoided them
for the
most part, but for sometimes mixing a little of them with my
own stuff. Got some nice 'whites' that way as looked like
the batter sorts of old time 'Milk Glass'...which, on a tan
Stoneware, was quite handsome.
Anyway...when I am back-in-the-saddle again on Glazing, I
will see what other things may do...
What decent Books have we so far as ^10 & ^11 Glazes?
Phil
el v
----- Original Message -----
From: "Paul Lewing"
> on 8/2/04 9:07 PM, pdp1@EARTHLINK.NET
>
> > What of Tin, Antimony, or Bismuth, in various forms?
> How are they for the qualities we seek in Glazes?
>
> As lead substitutes, not good. Lead is a flux. Tin is an
opacifier;
> antimony is a colorant. Bismuth is a flux, but I know
very little about it,
> except that it's expensive. Another of lead's advantages
is that it's
> incredibly cheap and abundant. As I say, it's the perfect
lowfire glaze
> base, except........
> Paul Lewing, Seattle
Ron Roy on wed 4 aug 04
If the lead frit is exposed to any reduction it will still fume - and there
is usually some reduction at certain stages in electric firing - potters
who use lead need to know more - not less about their craft.
RR
>However, it may not be as bad as you think. Fritted lead, like the
>bisilicate, does not volatilize at low-fire temperatures, so there is not
>that danger to your customers, which means that if you use a lead-free liner
>glaze, you can use them on the outsides of your pots. Of course, all the
>dangers to you from dust, etc. still remain.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ivor and Olive Lewis on thu 5 aug 04
Dear Friends,
I came across this site http://www.epa.gov/ttn/chief/le/lead1.pdf.
but only looked in the index. There are sections on the manufacture of
frits and on the pottery industries.
Sections 6-5 and 6-6 would seem to important to informing this
discussion.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
.
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