Pat Chesney on tue 18 nov 97
We are using a copper red glaze that gives excellent color in our wood
firing. It crazes badly on our stoneware body and it runs like water.
I know that all cu reds act up like this, but is there a way to make it
better behaved?
We fire with wood to cone 11. I know that this is hot for reds. We try to
load in cooler spots. It really looks good if we can stop the running. The
pots crackle and pop for a day or two after firing, but there is no
tendency to crack the pot-just many craze lines. On the occasional pot
where the some of the glaze goes clear, the crazing is much worse.
We have to glaze very heavily to get the good red color-this adds to losing
pots due to running.
If cu reds always run, is there a way to use a wad or something to enable
the runs to be cleaned up without unsightly grinding? At present, we glaze
very thin on the bottom 3/4 " and we can save 50%. Our standards allow for
no grinding to be sold as first quality.
I got this recipe from the list sometime back and I don't know for sure who
to give credit for it. Sorry.
Glaze name: Cranberry red
Cone: 10
Color: Transparent (thin)/ Opaque (thick) Red
Testing: tested
Surface texture: Shiny or Glossy
Firing: Reduction
Glaze type:
Recipe: Percent Batch
Neph Sye 44.26 13278
Flint 23.58 7074
Whiting 14.27 4281
Gerstley Borate 9.10 2730
Custer Feldspar 6.20 1860
Kaolin 2.59 777
Totals: 100.00 % 30000 Gm
Also add:
tin oxide 1.04 312
Copper carbonate 0.41 123
Possible Health Hazards:
Flint: free silica-wear a NIOSH approved dust mask when handling dry material
Unity Formula for Cranberry red:
0.098 K2O 0.410 Al2O3 3.251 SiO2
0.275 Na2O 0.129 B2O3
0.624 CaO
0.003 MgO
Percentage Analysis:
63.53 % SiO2
13.60 % Al2O3
2.93 % B2O3
2.99 % K2O
5.53 % Na2O
11.39 % CaO
0.03 % MgO
Pat Chesney
Pat-Chesney@easy.com
Waco, Texas
David Hendley on fri 21 nov 97
Pat, here are my thoughts on your red glaze:
I think a copper red glaze must be FLUID,
but that does not mean RUNNY.
If yours "runs like water" you need to adjust it to
fit your firing. I don't recall my copper red
ever running unless it was over-lapped with another glaze.
The unity formula for your glaze looks very
reasonable for a ^10 copper red glaze, in fact,
the Al2O3 at .410 is greater than most copper reds I have seen.
Since alumina keeps glazes from running, I'm puzzled
why it runs so badly. Maybe your kiln is getting hotter
than you realize? Could you back it down to ^10 and see what happens?
Maybe you just can't apply it so thick?
I also have to work at keeping my copper red from crazing,
and sometimes hear the occasional "ping" for several
days after a firing is unloaded. My glaze is not crazed all over
but it's hard to stop the stray stress cracks.
There are two reasons why you see a lot more crazing when
the glaze goes clear:
1~~it's just easier to see in a clear glaze,
2~~more importantly, when a pot is right in a strong flame
path in a wood kiln the flame and ashes will bleach the red
out of a copper red. The high-expansion fluxes in the ash change
the composition of the glaze and cause it to craze.
from 100 miles down the road,
David Hendley
At 08:02 AM 11/18/97 EST, you wrote:
>----------------------------Original message----------------------------
>We are using a copper red glaze that gives excellent color in our wood
>firing. It crazes badly on our stoneware body and it runs like water.
>
>I know that all cu reds act up like this, but is there a way to make it
>better behaved?
>
>We fire with wood to cone 11. I know that this is hot for reds. We try to
>load in cooler spots. It really looks good if we can stop the running. The
>pots crackle and pop for a day or two after firing, but there is no
>tendency to crack the pot-just many craze lines. On the occasional pot
>where the some of the glaze goes clear, the crazing is much worse.
>
>We have to glaze very heavily to get the good red color-this adds to losing
>pots due to running.
>
>If cu reds always run, is there a way to use a wad or something to enable
>the runs to be cleaned up without unsightly grinding? At present, we glaze
>very thin on the bottom 3/4 " and we can save 50%. Our standards allow for
>no grinding to be sold as first quality.
>
>I got this recipe from the list sometime back and I don't know for sure who
>to give credit for it. Sorry.
>
>Glaze name: Cranberry red
>Cone: 10
>Color: Transparent (thin)/ Opaque (thick) Red
>Testing: tested
>Surface texture: Shiny or Glossy
>Firing: Reduction
>Glaze type:
>
>Recipe: Percent Batch
>Neph Sye 44.26 13278
>Flint 23.58 7074
>Whiting 14.27 4281
>Gerstley Borate 9.10 2730
>Custer Feldspar 6.20 1860
>Kaolin 2.59 777
>Totals: 100.00 % 30000 Gm
>
>Also add:
>tin oxide 1.04 312
>Copper carbonate 0.41 123
>
>Possible Health Hazards:
>Flint: free silica-wear a NIOSH approved dust mask when handling dry material
>
>
>Unity Formula for Cranberry red:
>0.098 K2O 0.410 Al2O3 3.251 SiO2
>0.275 Na2O 0.129 B2O3
>0.624 CaO
>0.003 MgO
>
>Percentage Analysis:
> 63.53 % SiO2
> 13.60 % Al2O3
> 2.93 % B2O3
> 2.99 % K2O
> 5.53 % Na2O
> 11.39 % CaO
> 0.03 % MgO
>
>
>
>Pat Chesney
>Pat-Chesney@easy.com
>Waco, Texas
>
>
David Hendley
Maydelle, Texas
See David Hendley's Pottery Page at
http://www.sosis.com/hendley/david/
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