Paul Lewing on tue 23 may 00
Recently I have been fooling with a zinc base glaze and was reading up
on Bristol glazes. They were developed as a substitute for lead,
presumably for low-fire glazes, although one of my books mentions them
being used at midrange temperatures.
This is the base I've come up with:
Lewing Zn Base
Zinc Oxide 11.35
Gerstley Borate 10.79
Custer Feldspar 48.44
Whiting 4.05
Silica 20.45
EPK Kaolin 4.91
This is a recipe that was published in the current issue of Clay Times,
and I'm quite proud of it. It's the first glaze I've designed by just
making up an empirical formula using Insight, and it was ready to put
into my production line after only two 100g tests. If anyone out there
has used it, I'd like some feedback.
Anyway, my question is, is this a Bristol glaze? Is it only the fact
that it's a Zn base that makes a glaze a Bristol glaze, or is there some
further criterion? I can't find any in any of my books.
Thanks,
Paul Lewing, Seattle
John Hesselberth on wed 24 may 00
Hi Paul,
Most of the references I've looked at like Hamer & Hamer, Rhodes and
Norton just say high zinc, but a couple say a bit more. Parmelee and
Harmon, 3rd ed., p. 91 say "These unfritted glazes usually are applied to
raw or unfired bodies. Because...of this..the glaze should have a high
clay content."
Cardew in Pioneer Pottery, 1969 ed., p. 57 says "The advantages for
industrial stoneware are that the glaze, being leadless and unfritted is
very cheap...Secondly, these glazes can contain a high percentage of
clay...so can be more easily applied to raw goods." Leave it to Cardew
to look for "cheap" as hard as he struggled to keep going at times.
So both mention unfritted and high clay to allow them to be put on
greenware.
If you really want to dig more I can give you some references that might
get you started. Back in the golden age of glaze research, A.S. Watts
published several articles on Bristol glazes. The references I have are
in 1916 and 1917 and a typical one is "The Practical Application of
Bristol Glazes Compounded on the Eutectic Basis," Trans. Amer. Ceram.
Soc., XIX, 301-302 (1917). I suspect somewhere in his series of articles
he tells what he thinks a Bristol Glaze is from the perspective of 1917,
but I only have abstracts so I can't be sure. Those articles would all
give a series of references themselves though that might allow you to dig
back to a good defintion.
Before Watts, R. C. Purdy published articles on Bristol glazes, e.g.
"Further Studies on White Bristol Glazes," Trans. Amer. Ceram. Soc.., V,
136-167 (1903).
In a 1902 article, quoting from the abstract, Purdy defined a Bristol
glaze as "..one composed essentially of silicates of alkalies,
alkaline-earths, and alumina, applicable to green ware, and capable of
being burned in an open fire with slip glazes. Bristol glazes may be
either clear and colorless, white or colored." The reference here is
"Stoneware Glazes," Trans. Amer. Ceram. Soc., IV, 61-78 (1902).
Have fun. Reading the work of some of these folks never ceases to amaze
me. John
Paul Lewing wrote:
>Recently I have been fooling with a zinc base glaze and was reading up
>on Bristol glazes. They were developed as a substitute for lead,
>presumably for low-fire glazes, although one of my books mentions them
>being used at midrange temperatures.
>This is the base I've come up with:
>
>Lewing Zn Base
>Zinc Oxide 11.35
>Gerstley Borate 10.79
>Custer Feldspar 48.44
>Whiting 4.05
>Silica 20.45
>EPK Kaolin 4.91
>
>This is a recipe that was published in the current issue of Clay Times,
>and I'm quite proud of it. It's the first glaze I've designed by just
>making up an empirical formula using Insight, and it was ready to put
>into my production line after only two 100g tests. If anyone out there
>has used it, I'd like some feedback.
>Anyway, my question is, is this a Bristol glaze? Is it only the fact
>that it's a Zn base that makes a glaze a Bristol glaze, or is there some
>further criterion? I can't find any in any of my books.
>Thanks,
>Paul Lewing, Seattle
>
>__________________________________________________________________________
>____
>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.
John Hesselberth
Frog Pond Pottery
P.O. Box 88
Pocopson, PA 19366 USA
EMail: john@frogpondpottery.com web site: http://www.frogpondpottery.com
"Pots, like other forms of art, are human expressions: pleasure, pain or
indifference before them depends upon their natures, and their natures
are inevitably projections of the minds of their creators." Bernard
Leach, A Potter's Book.
Craig Martell on wed 24 may 00
Paul Lewing axed:
>Anyway, my question is, is this a Bristol glaze? Is it only the fact
>that it's a Zn base that makes a glaze a Bristol glaze, or is there some
>further criterion? I can't find any in any of my books.
Hey Paul:
Damifino!! It's a bristol glaze if you say so!!
Parmelee gives this as the empirical formula for a "typical" bristol glaze.
0.35 KNaO
0.35 CaO
0.30 ZnO
0.60 Al2O3
3.50 SiO2
I looked at the seger for your glaze and you are certainly in the
ballpark. Maybe Parmelee had some kind of stigma about boron or maybe
boron technically negates a glaze as being a true "bristol". I don't
know. The alumina is high because he says these glazes were usually
applied to unfired ware so you'd need some extra clay for raw glazing. You
might make up the above formula and see how it compares to yours.
regards, Craig Martell in Oregon
Dwiggins, Sandra (NCI) on wed 24 may 00
I thought that Bristol Glazes also had a particular surface texture. I
don't remember exactly, but I think they were a semi-matte opaque glaze or
matte surface rather than glossy. So, there are certain characteristics.
I'll bet R.R. or Vince will have the answer!
Sandy
> -----Original Message-----
> From: Paul Lewing [SMTP:pjlewing@WORLDNET.ATT.NET]
> Sent: Tuesday, May 23, 2000 12:43 PM
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Bristol glaze?
>
> Recently I have been fooling with a zinc base glaze and was reading up
> on Bristol glazes. They were developed as a substitute for lead,
> presumably for low-fire glazes, although one of my books mentions them
> being used at midrange temperatures.
> This is the base I've come up with:
>
> Lewing Zn Base
> Zinc Oxide 11.35
> Gerstley Borate 10.79
> Custer Feldspar 48.44
> Whiting 4.05
> Silica 20.45
> EPK Kaolin 4.91
>
> This is a recipe that was published in the current issue of Clay Times,
> and I'm quite proud of it. It's the first glaze I've designed by just
> making up an empirical formula using Insight, and it was ready to put
> into my production line after only two 100g tests. If anyone out there
> has used it, I'd like some feedback.
> Anyway, my question is, is this a Bristol glaze? Is it only the fact
> that it's a Zn base that makes a glaze a Bristol glaze, or is there some
> further criterion? I can't find any in any of my books.
> Thanks,
> Paul Lewing, Seattle
>
> __________________________________________________________________________
> ____
> 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.
Gregory D Lamont on wed 24 may 00
At 03:57 PM 5/24/00 -0400, you wrote:
>I thought that Bristol Glazes also had a particular surface texture. I
>don't remember exactly, but I think they were a semi-matte opaque glaze or
>matte surface rather than glossy. So, there are certain characteristics.
>I'll bet R.R. or Vince will have the answer!
>
>Sandy
>
> > -----Original Message-----
> > From: Paul Lewing [SMTP:pjlewing@WORLDNET.ATT.NET]
> > Sent: Tuesday, May 23, 2000 12:43 PM
> > To: CLAYART@LSV.CERAMICS.ORG
> > Subject: Bristol glaze?
> >
> > Recently I have been fooling with a zinc base glaze and was reading up
> > on Bristol glazes. They were developed as a substitute for lead,
> > presumably for low-fire glazes, although one of my books mentions them
> > being used at midrange temperatures.
> > This is the base I've come up with:
> >
> > Lewing Zn Base
> > Zinc Oxide 11.35
> > Gerstley Borate 10.79
> > Custer Feldspar 48.44
> > Whiting 4.05
> > Silica 20.45
> > EPK Kaolin 4.91
> >
> > This is a recipe that was published in the current issue of Clay Times,
> > and I'm quite proud of it. It's the first glaze I've designed by just
> > making up an empirical formula using Insight, and it was ready to put
> > into my production line after only two 100g tests. If anyone out there
> > has used it, I'd like some feedback.
> > Anyway, my question is, is this a Bristol glaze? Is it only the fact
> > that it's a Zn base that makes a glaze a Bristol glaze, or is there some
> > further criterion? I can't find any in any of my books.
> > Thanks,
> > Paul Lewing, Seattle
Hi Paul,
I've been reading up on Maija Grotell, a potter who emigrated from Norway
to this country back in 1925, studied with C. F. Binns at Alfred, and
taught ceramics at Cranbrook Academy for many years. She had a method of
glazing, described in the book, whereby she first brushed on a layer of
Albany slip, then brushed on a white Bristol glaze over that. Apparently,
a characteristic of Bristol-type glazes is that they are very stiff. The
fluid Albany slip would boil up through the top layer of glaze creating a
"leopard spot" effect. She fired to cone 8 in an Alpine "Globar"
(electric) kiln and cooled very slowly, allowing the surface to smooth out.
I will be experimenting with this technique for a class assignment, and
will be trying some of my own "stiff" glazes in addition to a zinc-base
"Bristol" glaze. My instructor suggested I also try a glaze we have called
Mamo--a nice matte glaze. Ideally, I'd like to get the effect to work at
cone 6.
Greg
E-mail address:
gdlamont@isunet.net
Pottery Web Page:
http://www.ourwebpage.net/greglamont/
Mailing address and Phone:
Greg Lamont
3011 Northwood Drive
Ames, IA 50010-4750
(515) 233-3442
Khaimraj Seepersad on thu 25 may 00
Good Day to All ,
Craig -
I believe your not supposed to use Alkali's , Zinc and Boron together
with out caution . They may increase each other's solubility in water
, acids or alkali's .
Plus isn't the temperature [ above 1100 deg.c ] supposed to be
optional for zinc's activity as a flux , with out needing Boric Oxide to
keep it in solution ?
Khaimraj Seepersad
-----Original Message-----
From: Craig Martell
To: CLAYART@LSV.CERAMICS.ORG
Date: 25 May 2000 7:04
Subject: Re: Bristol glaze?
>Paul Lewing axed:
>
>>Anyway, my question is, is this a Bristol glaze? Is it only the fact
>>that it's a Zn base that makes a glaze a Bristol glaze, or is there some
>>further criterion? I can't find any in any of my books.
>
>Hey Paul:
>
>Damifino!! It's a bristol glaze if you say so!!
>
>Parmelee gives this as the empirical formula for a "typical" bristol glaze.
>
>0.35 KNaO
>0.35 CaO
>0.30 ZnO
>0.60 Al2O3
>3.50 SiO2
>
>I looked at the seger for your glaze and you are certainly in the
>ballpark. Maybe Parmelee had some kind of stigma about boron or maybe
>boron technically negates a glaze as being a true "bristol". I don't
>know. The alumina is high because he says these glazes were usually
>applied to unfired ware so you'd need some extra clay for raw glazing. You
>might make up the above formula and see how it compares to yours.
>
>regards, Craig Martell in Oregon
Craig Martell on fri 26 may 00
Khaimraj sez:
>I believe your not supposed to use Alkali's , Zinc and Boron together
>with out caution . They may increase each other's solubility in water
>, acids or alkali's .
>
>Plus isn't the temperature [ above 1100 deg.c ] supposed to be
>optional for zinc's activity as a flux , with out needing Boric Oxide to
>keep it in solution ?
Hello Khaimraj:
Before rambling on too much about this, I'll give you my short answer. I
dunno!!
I would think that the source of boron might be a concern. If you used a
boron frit, solubility would not be a problem. Gerstley borate, on the
other hand, is always problematic. I did some reading in a minerals text
about Ulexite, which is the source of gerstley borate. According to the
text, written by Chris Pellant of the UK, Ulexite is insoluble in cold
water, but soluble in hot water. So water temp may be a factor here. How
hot is hot? Don't know!!
I've seen quite a few copper red formulas for cone 9-10 R that contain both
boron and zinc, in smaller quantities. I don't have any confirmation that
this is a correct or effective use of these fluxes, I just know that they
are used together at hi temp.
I guess the deal is that a true bristol doesn't need any boron, just ZnO,
CaO, and KNaO.
over and out, Craig Martell in Oregon
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