iandol on fri 22 nov 02
Well Folks,
I opened the kiln this morning. Not quite dead cold but no chance of a =
bare handed burn.
Kiln fired without deliberate reduction to Orton C 8 well over. Greatest =
set of test tiles I have ever produced. the 3 X36 tiles with the crazing =
pre-emptive strike gave 108 uncrazed samples and a lot of things to =
think about.
The X36 Raw ash glaze mixtures crazed in the high Calcium region of the =
tile. I will follow this one up substituting some clay or other for the =
pure silica. The craze samples were very fluid.
Using a well trusted clear base loaded with increments of Barium Carb. =
Up to 20%. High Gloss transparent glazes. 25%, 30%, 35% &40% all =
transparent with progressively greater degrees of crazing. No signs of =
the opacity or mattness I was expecting. Image sent to Janet K.
X36 tile with mixtures of Felspar mix (4/1 Na Feld/Petalite), =
Wollastonite, Barium Carbonate and Talc. Image sent to Janet K.
Made the following observations.
Crazing increases with increasing BaO.
Crazing decreases with increasing felspar.
Porosity increases with increasing BaO.
Porosity decreases with increasing MgO and increasing felspar.
Viscosity increases with increasing BaO.
Surface tension decreases with increasing BaO.
Both MgO and CaO promote high surface tension but as a mixture they =
lower this factor.
When MgO is high it tends to come out of solution during cooling causing =
opacity
When CaO is high it stays in solution on cooling giving transparency.
Solubility of MgO increases with increasing BaO and decreasing felspar.
Solubility of CaO is unaffected by BaO
Opacity increases with increasing Felspar content and reducing BaO. .
Opacity increases with increasing Felspar content and increasing MgO.
Opacity increases with increasing Felspar content and decreasing CaO.
Tests with Local Slate Powder. Looking for a set of strange results. =
Lots of outgassing. Very high viscosity. Great Lava effect. And remember =
the "Electrostatic Effect" I spoke of a couple of years ago. This stuff =
has it in Spades, Aces High. Keeps on giving the "zaps", time and time =
again. Seems to be recharging itself. I think this would need a lot more =
heat or a boron frit to get a useable set of glazes.
Well, I think there were 230 new samples in that kiln and I am one Happy =
Little Dingo.
Best regards to all,
Ivor Lewis. Redhill, South Australia
Janet Kaiser on sat 23 nov 02
The two test tiles referred to in Ivor's post are to be seen at
http://www.clayart.fsnet.co.uk/glaze.html
Sincerely
Janet Kaiser
*********** REPLY SEPARATOR ***********
On 22/11/02 at 14:22 iandol wrote:
>Well Folks,
>I opened the kiln this morning. Not quite dead cold but no chance of a
>bare handed burn.
>Kiln fired without deliberate reduction to Orton C 8 well over. Greatest
>set of test tiles I have ever produced. the 3 X36 tiles with the crazing
>pre-emptive strike gave 108 uncrazed samples and a lot of things to think
>about.
>The X36 Raw ash glaze mixtures crazed in the high Calcium region of the
>tile. I will follow this one up substituting some clay or other for the
>pure silica. The craze samples were very fluid.
>Using a well trusted clear base loaded with increments of Barium Carb. Up
>to 20%. High Gloss transparent glazes. 25%, 30%, 35% &40% all transparent
>with progressively greater degrees of crazing. No signs of the opacity or
>mattness I was expecting. Image sent to Janet K.
>X36 tile with mixtures of Felspar mix (4/1 Na Feld/Petalite),
>Wollastonite, Barium Carbonate and Talc. Image sent to Janet K.
>
>Made the following observations.
>
>Crazing increases with increasing BaO.
>Crazing decreases with increasing felspar.
>Porosity increases with increasing BaO.
>Porosity decreases with increasing MgO and increasing felspar.
>Viscosity increases with increasing BaO.
>Surface tension decreases with increasing BaO.
>Both MgO and CaO promote high surface tension but as a mixture they lower
>this factor.
>When MgO is high it tends to come out of solution during cooling causing
>opacity
>When CaO is high it stays in solution on cooling giving transparency.
>Solubility of MgO increases with increasing BaO and decreasing felspar.
>Solubility of CaO is unaffected by BaO
>Opacity increases with increasing Felspar content and reducing BaO. .
>Opacity increases with increasing Felspar content and increasing MgO.
>Opacity increases with increasing Felspar content and decreasing CaO.
>
>Tests with Local Slate Powder. Looking for a set of strange results. Lots
>of outgassing. Very high viscosity. Great Lava effect. And remember the
>"Electrostatic Effect" I spoke of a couple of years ago. This stuff has it
>in Spades, Aces High. Keeps on giving the "zaps", time and time again.
>Seems to be recharging itself. I think this would need a lot more heat or
>a boron frit to get a useable set of glazes.
>Well, I think there were 230 new samples in that kiln and I am one Happy
>Little Dingo.
>Best regards to all,
>Ivor Lewis. Redhill, South Australia
Janet Kaiser
The Chapel of Art =95 Capel Celfyddyd
8 Marine Crescent, Criccieth LL52 0EA, Wales, UK
Tel: 01766-523570 URL: http://www.the-coa.org.uk
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