Lois Atherton on tue 7 nov 00
Hi,
I've just unloaded my kiln and have a question for anyone kind enough to try
an answer.
I've been using Pinnell's Blue Celadon with lovely color results. I fire
cone 10 with reduction starting at cone 010. I'm using a domestic porcelain.
Trouble is that quite often I'll get little tiny pulls of glazes off the
edges of bowls and vases....sort of healed over pinholes. A totally gorgeous
glaze with a little torture device....they aren't big enough to keep me from
using the glaze, but re-firing with little dobs of glaze gets old too!
Pete's Blue Celadon
Custer (Potash) Feldspar 25.0
Whiting 20.0
Grolleg Kaolin 20.0
Flint 35.0
Add :
Tin Oxide 1.0
Barium Carbonate 2.0
Barnard Clay 3.0
Thanks!
Lois
Sparrow House Pottery
Plymouth, MA
Tom Buck on sun 21 jan 01
Perhaps you do not need this now. But I was doing some writing in Nov and
had to put off some things.
The basic problem with the Pinnell CB is WHITING, and 20 units is
a lot of CO2 coming above 1800 F/1000 C. BTW Whiting is 44% CO2 and 56%
CaO. You need a good soak to heal the burst bubbles, and where the glaze
is thin healing may not occur even then.
The solution is to replace the Whiting with Wollastonite
(CaO.SiO2) and when you do this the Silica/Flint needs changing too.
here is how it comes out
30 Custer fs
25 Wollastonite
21 Grolleg
24 Flint
additives as before.
Molecularly, the two recipes provide the same amounts of fluxes
and glass-formers. It still will be glossy and with the same
expansion/contraction.
til later. Peace. Tom B.
Tom Buck ) tel: 905-389-2339
(westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street,
Hamilton ON L8T 3E1 Canada
On Tue, 7 Nov 2000, Lois Atherton wrote:
> Hi,
> I've just unloaded my kiln and have a question for anyone kind enough to try
> an answer.
> I've been using Pinnell's Blue Celadon with lovely color results. I fire
> cone 10 with reduction starting at cone 010. I'm using a domestic porcelain.
> Trouble is that quite often I'll get little tiny pulls of glazes off the
> edges of bowls and vases....sort of healed over pinholes. A totally gorgeous
> glaze with a little torture device....they aren't big enough to keep me from
> using the glaze, but re-firing with little dobs of glaze gets old too!
> Pete's Blue Celadon
> Custer (Potash) Feldspar 25.0
> Whiting 20.0
> Grolleg Kaolin 20.0
> Flint 35.0
> Add :
> Tin Oxide 1.0
> Barium Carbonate 2.0
> Barnard Clay 3.0
> Thanks!
> Lois
> Sparrow House Pottery
> Plymouth, MA
>
> ______________________________________________________________________________
> 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.
>
Craig Martell on mon 22 jan 01
Senor Tom Buck sez:
>Perhaps you do not need this now.
Hi Tom:
Sure we do!
>The basic problem with the Pinnell CB is WHITING, and 20 units is
>a lot of CO2 coming above 1800 F/1000 C. BTW Whiting is 44% CO2 and 56%
>CaO. You need a good soak to heal the burst bubbles, and where the glaze
>is thin healing may not occur even then.
>The solution is to replace the Whiting with Wollastonite
I think you are right on the money here. The whiting in molecular formula
in this glaze is about .79. That's quite a bit for a blue celadon and with
that much you are liberating a lot of CO2. John Britt sent me a mug with
this very same glaze though and it was flawless, not a bubble or a craze
line anywhere. Beautiful. The claybody was a Grolleg Porcelain though and
perhaps that was a help or John has the quintessential firing schedule for
this glaze.
The blue celadons that I've made are based on Tichane's .3 K2O, .7CaO blue
celadon. The closest that I've been able to be to that formulae
is: .3K2O, .1Na2O, and .6CaO, due to the fact that pure potash feldspars
don't exist in nature. This flux formula works well though and at .6 CaO I
can use whiting without flaws from bubbles. I will however give this
formula a shot with Wollastonite.
regards, Craig Martell in Oregon
| |
|
