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50 hours to bristol was re: mocha and bristol

updated fri 21 jan 05

 

Daniel Semler on tue 18 jan 05


Hi Lili,

> Most curious is that for a formula 0.35KNaO, 0.35 CaO, 0.30ZnO, 0.55 Al2O3,
> 3.30 SiO2 he speaks of "stoneware fired at cones 6-7 in 50-60 hours"
> !!!!!!!!!!

I too noticed this. I have yet to find an explanation for it. Misprint perhaps ?
Or was such a cycle used for other reasons ? Even once-firing does not seem to
account for it.

Thanx
D

John K Dellow on wed 19 jan 05


Daniel Semler wrote:

>Hi Lili,
>
>
>
>>Most curious is that for a formula 0.35KNaO, 0.35 CaO, 0.30ZnO, 0.55 Al2O3,
>>3.30 SiO2 he speaks of "stoneware fired at cones 6-7 in 50-60 hours"
>>!!!!!!!!!!
>>
>>
>
>I too noticed this. I have yet to find an explanation for it. Misprint perhaps ?
>Or was such a cycle used for other reasons ? Even once-firing does not seem to
>account for it.
>
>Thanx
>D
>
>______________________________________________________________________________
>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.
>
>
>
>
Its because kilns in those days were made of hard brick and too a long
to fire. If you make up a bristal glaze and fire to the correct cone in
a fibre kiln , the glaze will be under fired.
John

--

John Dellow "the flower pot man"
From the land down under
Home Page http://www.welcome.to/jkdellow
http://digitalfire.com/education/people/dellow/

Ivor and Olive Lewis on wed 19 jan 05


> > Most curious is that for a formula 0.35KNaO, 0.35 CaO, 0.30ZnO,
0.55 Al2O3, 3.30 SiO2 . he speaks of "stoneware fired at cones 6-7 in
50-60 hours"
> > !!!!!!!!!!

Dear Daniel Semler,
If this glaze was being used in an industrial situation they may have
had ten tons of ware in that kiln. It may also have been a very
inefficient kiln with regard to the refractories with little
insulation power.
If you read back through the literature for Bristol Glazes, they were
devised in the first instance for industrial use. When studying a
glaze pay attention to the context in which it would have been used or
developed. By the way, is it certain that this was a cone 6 - 7 glaze
and that it was not made to mature in the cone 3 - 4 range?

Best regards,
Ivor Lewis.
Redhill,
S. Australia.

Daniel Semler on wed 19 jan 05


Hi Ivor, John,

After reading John's response I had begun heading in the direction of
it-must-be-a-large-kiln. Makes sense.

> When studying a
> glaze pay attention to the context in which it would have been used or
> developed.

A good point.

> By the way, is it certain that this was a cone 6 - 7 glaze
> and that it was not made to mature in the cone 3 - 4 range?

Well, without testing it I don't really know, but that's certainly what the text
says. Parmalee & Harman also list other compositions, ranging from 03 upwards.
Apparently there are compositions throughout the stoneware range and into
electrical porcelain - cone 14.

I am tempted to obtain A.S. Watts 1916 and 1917 papers on Bristol glazes in
which he studied a number of compositions, based on eutectics I believe.

Thanx
D

Ivor and Olive Lewis on thu 20 jan 05


Dear John Dellow,
You suggest <and took a long to fire. If you make up a bristal glaze and fire to
the correct cone in a fibre kiln , the glaze will be under fired.>>
This is because the ancient brick kiln took a long time to cool. The
additional heat radiating from the brickwork over those extra hours
allowed time for the refractory Zinc Oxide to dissolve in the melt
created from the raw materials containing Alkali Metal oxides. The
alternatives when using small RI brick or fibre lined kilns are to
fire at a much higher temperature, possibly above cone 12 or extend
the firing time by several hours.
Best regards.
Ivor Lewis.
Redhill,
S. Australia.


----- Original Message -----
From: "John K Dellow"
To:
Sent: Wednesday, 19 January 2005 8:01
Subject: Re: 50 hours to Bristol was Re: mocha and bristol


> Daniel Semler wrote:
>
> >Hi Lili,
> >
> >
> >
> >>Most curious is that for a formula 0.35KNaO, 0.35 CaO, 0.30ZnO,
0.55 Al2O3,
> >>3.30 SiO2 he speaks of "stoneware fired at cones 6-7 in 50-60
hours"
> >>!!!!!!!!!!
> >>
> >>
> >
> >I too noticed this. I have yet to find an explanation for it.
Misprint perhaps ?
> >Or was such a cycle used for other reasons ? Even once-firing does
not seem to
> >account for it.
> >
> >Thanx
> >D
> >
>
>_____________________________________________________________________
_________
> >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.
> >
> >
> >
> >
> Its because kilns in those days were made of hard brick and too a
long
> to fire. If you make up a bristal glaze and fire to the correct cone
in
> a fibre kiln , the glaze will be under fired.
> John
>
> --
>
> John Dellow "the flower pot man"
> From the land down under
> Home Page http://www.welcome.to/jkdellow
> http://digitalfire.com/education/people/dellow/
>
>
______________________________________________________________________
________
> 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.

Ivor and Olive Lewis on thu 20 jan 05


Dear Daniel Semler,
You should read Watts. He is well worth the effort.
Excluding John H. and Ron R. from this generalisation, I wish most of
the people who have been writing about glazes and publishing their
ideas had done so before they rushed into print.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.

John Hesselberth on thu 20 jan 05


On Wednesday, January 19, 2005, at 10:10 PM, Daniel Semler wrote:

> I am tempted to obtain A.S. Watts 1916 and 1917 papers on Bristol
> glazes in
> which he studied a number of compositions, based on eutectics I
> believe.

Hi Daniel,

I have abstracts of 2 of his articles from that time period in which he
states the most fusible of modern Bristol glazes to be 0.4KNaO, 0.3
CaO, 0.3 ZnO, 0.6 Al2O3, 3.55 SiO2.

The recipe he gives for a deformation temperature of cone 03 is
Canadian Feldspar 59.62
Whiting 8.03
Zinc Oxide 6.5
Florida Kaolin 13.81
Flint 12.04

Using G-200 and EPK I come pretty close to his unity formula with the
above recipe--but not dead on.

Regards,

John
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com

Daniel Semler on thu 20 jan 05


Hi John,

Thanx for this.

Parmalee reports this composition too, in reference to Watts' work.
I tried custer and found it out a bit, probably much like your G200, I'd
think.
I tried Kona F4 and then tweaked the percentages a little and it looked good,
though the expansion was probably up a little.

I have often thought about the abstracts. You've mentioned them before I
think, or maybe I saw it in your paper on limits on your website. I've not
seen them. I have the impression that the abstracts of the published articles
are bundled up into volumes and published. Is this so ? How useful do you find
them ? Do they have enough of the text in the abstracts to make them useful ?

Thanx
D

John Hesselberth on thu 20 jan 05


Hi Daniel,

I find the book fairly useful. The book is titled Literature Abstracts
of Ceramic Glazes and was compiled by Koenig and Earhart. The 1951
edition is the one to look for if you are interested. I think that was
the last one, though I am not sure. It has about 380 pages moderately
well indexed--by subject, not author. It abstracts about 20 journals
from the early 1900s to 1950--the glory years of glaze research.

When I did the literature study on limit formulas I felt comfortable
just using the abstract (which sometimes runs more than a page for a
single article--sometimes just a few lines) about half the time in the
articles of interest to me. The other half I went ahead a got the full
article from ACerS. If you have a fax near by I'll fax you the pages on
Watts two articles of that period so you can get an idea for yourself
as to the level of detail.

As a side note I found interesting. My copy came from the Franklin
Institute Library. It still has the library card inside--it was only
checked out twice in the years they had it. So it was not exactly a
best seller. But it is good bedside reading for glaze addicts.

Regards,

John


On Thursday, January 20, 2005, at 01:29 PM, Daniel Semler wrote:

> Hi John,
>
> Thanx for this.
>
> Parmalee reports this composition too, in reference to Watts' work.
> I tried custer and found it out a bit, probably much like your G200,
> I'd
> think.
> I tried Kona F4 and then tweaked the percentages a little and it
> looked good,
> though the expansion was probably up a little.
>
> I have often thought about the abstracts. You've mentioned them
> before I
> think, or maybe I saw it in your paper on limits on your website.
> I've not
> seen them. I have the impression that the abstracts of the published
> articles
> are bundled up into volumes and published. Is this so ? How useful do
> you find
> them ? Do they have enough of the text in the abstracts to make them
> useful ?
>
> Thanx
> D
>
> _______________________________________________________________________
> _______
> 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
http://www.frogpondpottery.com
http://www.masteringglazes.com