Craig Martell on tue 1 aug 00
Hi:
I've had a lot of off list as well as on list responses to my blue celedon
post so I thought I'd have a go at a quick response and then do some follow
up stuff later and address some of the posts more thoroughly.
Here is the basic recipe that produced a blue celedon for me. I've
included the seger formula so folks abroad can plug in their raw materials
if they want to try this glaze. Here 'tis, without the colorant which is
1% black iron oxide. I used black iron because I've been told that black
iron will produce blue celedons more readily than other types of iron. I
will test red iron and yellow iron in this base and give you all my
results. Also, Kingman is a potash spar that is no longer available. In
the oxide analysis, it contains 12% potassium, as does kona a-3 potash
spar. Custer and g-200 have about 10% potassium.
Blue Celedon cone 10R
=====================
Kingman feldspar.... 55.17 55.17%
whiting............. 14.15 14.15%
silica.............. 30.68 30.68%
========
100.00
CaO 0.60* 8.53%
K2O 0.30* 7.07%
Na2O 0.10* 1.65%
Al2O3 0.43 11.02%
SiO2 4.70 71.67%
Fe2O3 0.00 0.07%
Cost/kg 0.04
Si:Al 11.04
SiB:Al 11.04
Expan 7.45
This glaze is as close as I can come to Tichane's sky blue celedon seger
formula with the raw materials that are available to us here in the US. I
don't want to use frits. It's a well balanced, durable glaze and this
seger is totally food safe etc. The thing I like is that there is enough
alumina in the glaze without an addition of clay. For suspension, I added
2% Hecta Brite, which is a brand of hectorite. You can use macaloid or vee
gum cer to suspend the glaze. If you need to use kaolins in a blue
celedon, use grolleg which is a kaolin very low in titanium. If you have
blue celedons that you are currently using with other kaolins such as EPK
or Tile #6, try subbing grolleg and you'll see an improvement in color. As
John Britt pointed out, the clay body is important for the blues too. If
your clay has a considerable amount, or maybe even just some titanium. Try
a grolleg porcelain slip over your body to improve the blue. My suggestion
for a starting point would be: 50% grolleg, 25% potash feldspar, and 25%
silica for the slip.
That's about it for now. I just got back from helping my wife at a show
and I'm amazed that I was able to write this much. :>) Yawn!!!
later, Craig Martell in Oregon
James Bowen on mon 24 mar 03
I saw some ancient Chinese Song Dynasty pots once that
looked like
porcelain, and were glazed in a transparent
Caribbean blue glaze. The white of the porcelain shows
through and the glaze pools in surface marks beautifully. I
have always thought of this as Blue Celadon. Am I wrong?
"Ours is a world of nuclear giants and ethical infants. We
know more about war than we know about peace, more about
killing than we know about living. We have grasped the
mystery of the atom and rejected the Sermon on the Mount. "
Omar Bradley, World War II General and Chairman of the Joint
Chiefs of Staff under Harry Truman
iandol on tue 25 mar 03
Dear James Bowen,
You are probably correct in your assumption. I read that Sky Blue was a =
treasured colour. Light, Translucent, Vitreous sonorous bodies were =
known during the Song Era.
Blue becomes possible when the level of Titanium Dioxide is low in both =
the rocks from which the clay is formed and in the rocks which =
contribute to the glaze.
Best regards,
Ivor Lewis, Redhill, South Australia
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