Jeff Lawrence on wed 10 oct 01
Hi,
There is a glaze in the local studio I'm using that
is a favorite cone 5 electric shiny glaze:
50 gerstley
25 neph sy
25 epk
10 tin oxide
They tell me that in reduction it is a stony matt. I'll be
putting a test in a firing soon but am curious why this
glaze would lose its gloss in reduction.
Any theories?
TIA
JEff
Hank Murrow on thu 11 oct 01
>Hi,
>
>There is a glaze in the local studio I'm using that
>is a favorite cone 5 electric shiny glaze:
>50 gerstley
>25 neph sy
>25 epk
>10 tin oxide
>
>They tell me that in reduction it is a stony matt. I'll be
>putting a test in a firing soon but am curious why this
>glaze would lose its gloss in reduction.
>
>Any theories?
>
>TIA
>JEff
Dear Jeff;
Reduction often causes glazes to melt more completely. I have two
bowls made by David Stannard from a porcelain stone he mines and processes.
One is fired to C/9 in electric Ox, the other C/9 in Reduction. The glaze
is the body with 15% limestone added, which gives a celadon in Reduction
and a white matt in Ox. Only very tiny (perhaps .25%) iron in the glaze.
I'll bet if water vapor was introduced into the electric at high
temperature somehow, your glaze would shine out.
Hank in Eugene
Liisa Reid on thu 11 oct 01
Jeff -
A theory: different cooling rates: a fast cooling will prevent crystal
formation. The slower cooling typical of a gas kiln will promote crystal
formation. True mats (as opposed to alumina mats) depend on formation of micro
crystals. Just a theory. I'd be curious to know the answer if you figure it out.
Liisa
reidpots@together.net
John Weber on fri 12 oct 01
Hank responded to the following with " I'll bet if water vapor was
introduced into the electric at high
> temperature somehow, your glaze would shine out." Could Hank or anyone
else please elaborate on why the introduction of water vapor at high heat
would cause a matt glaze to become shiny? Thanks.
> -----Original Message-----
> From: Ceramic Arts Discussion List [mailto:CLAYART@LSV.CERAMICS.ORG]On
> Behalf Of Hank Murrow
> Sent: Thursday, October 11, 2001 6:54 AM
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Re: shiny vs matt glaze question
>
>
> >Hi,
> >
> >There is a glaze in the local studio I'm using that
> >is a favorite cone 5 electric shiny glaze:
> >50 gerstley
> >25 neph sy
> >25 epk
> >10 tin oxide
> >
> >They tell me that in reduction it is a stony matt. I'll be
> >putting a test in a firing soon but am curious why this
> >glaze would lose its gloss in reduction.
> >
> >Any theories?
> >
> >TIA
> >JEff
>
> Dear Jeff;
>
> Reduction often causes glazes to melt more completely. I have two
> bowls made by David Stannard from a porcelain stone he mines and
> processes.
> One is fired to C/9 in electric Ox, the other C/9 in Reduction. The glaze
> is the body with 15% limestone added, which gives a celadon in Reduction
> and a white matt in Ox. Only very tiny (perhaps .25%) iron in the glaze.
>
> I'll bet if water vapor was introduced into the electric at high
> temperature somehow, your glaze would shine out.
>
> Hank in Eugene
>
> __________________________________________________________________
> ____________
> 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.
>
Hank Murrow on mon 28 jan 02
John Weber wrote;
>Hank responded to the following with " I'll bet if water vapor was
>introduced into the electric at high
>> temperature somehow, your glaze would shine out." Could Hank or anyone
>else please elaborate on why the introduction of water vapor at high heat
>would cause a matt glaze to become shiny? Thanks.
Dear John;
The research done by the batelle institute back in the sixties
showed that water vapor @ high temps disasociated into Hydrogen and Oxygen.
The H2 served to reduce the oxides in clay and glaze. natural gas contains
several % water, and may be the reason propane seems to require 'more'
reduction to mature the glazes. BTW, have apeek at my site beginnings @
http://www.murrow.biz/hank, and click on the pic at the beginning as soon
as it has loaded. You can navigate from there, according to interest.
Hope this makes sense, Hank
| |
|
