Chris Jones on tue 8 jul 03
Hey Paul,
Do you have any pictures of what you are doing? I think I use the same glaze
and might have a little help although I am not a glaze guru.
Chris Jones
Jones Pottery
Amelia Island, FL
www.jonespottery.net
chris@jonespottery.net
Paul on tue 8 jul 03
Hello,
I posted some questions about rutile blue glazes several months ago and
received many helpful responses. I did find that faster cooling makes a big
difference in helping the color come out before the glaze opacifies into a
white mat color. I still am adjusting the cooling cycle to get it just
right, but i recently came across another mystery.
I tried subsitituting some agricultural-grade limestone i bought at a
farmer's co-op for $1.50 for a 50lb bag. They called it dolomite-lime,
compared to another type of limestone they sell that is hydrated-lime.
Anyway, i took out the whiting and added this stuff and it definitely helps
the color response, although in some pieces there were more pinholes than
usual.
Does anyone know why this may help the color develop better? I know there
must be some iron in it that could help but i don't know if that accounts
for all the difference. Also, can anyone advise how to adjust the formula
to limit the pinholes should i decide to go with this new recipe? Any advice
is appreciated. Here is the original recipe again:
Dolomite 15.8
custer spar 30.0
whiting 11.1
epk 16.8
flint 26.3
rutile 8
fired to cone 10/11 reduction.
Thanks!
Paul B
David Hendley on thu 10 jul 03
I am responding to Paul's message because my experience is so completely
opposite. He says:
> I did find that faster cooling makes a big
> difference in helping the color come out before the glaze opacifies into a
> white mat color.
I have been actively working on slowing down the cooling of my kiln, and
I find that slow cooling helps immensely in the development of my rutile
blue glaze, as well as my copper red, which uses the same base.
I'm talking about a really slow cool. I used to wait about 40 hours to
crack the kiln. Now, about an hour and a half or two after shut down,
I really seal up the kiln, using clay to fill in cracks and a sheet of steel
to seal over the passive damper area, and it is still too hot to open after
48 hours. My rutile blue has a wonderful depth and richness.
I think the difference in our experiences has to do with the amount of
rutile in the glaze. Paul is using 8% rutile. In my situation, 8% rutile
added
to this glaze makes a creamy white glaze. Indeed, I also use the glaze in
this way (with 7% rutile).
For my rutile blue color I use 3% rutile.
I think the amount of titanium require to produce a good blue is
related to the cooling rate of the kiln.
Pinholing is a common problem when using a glaze with a large amount
of rutile (anything over about 5 or 6%).
Therefore, I would suggest that it is better to use less rutile in the
glaze,
in conjunction with a slower cooling cycle.
The amount of rutile in the glaze is very critical when designing a rutile
blue glaze. Just one half of one percent can make a big difference in the
color. Anyone who want to develop a good rutile blue glaze needs to
run a rutile line blend test to see what amount of rutile is optimum for
their situation.
As for the agricultural limestone, it is pretty much an unknown. It could
be mostly calcium, or have a lot of magnesium. There could also be a
difference because ag lime is often not as finely ground as ceramic grade
whiting.
David Hendley
david@farmpots.com
http://www.farmpots.com
----- Original Message -----
> I posted some questions about rutile blue glazes several months ago and
> received many helpful responses. I did find that faster cooling makes a
big
> difference in helping the color come out before the glaze opacifies into a
> white mat color. I still am adjusting the cooling cycle to get it just
> right, but i recently came across another mystery.
> I tried subsitituting some agricultural-grade limestone i bought at a
> farmer's co-op for $1.50 for a 50lb bag. They called it dolomite-lime,
> compared to another type of limestone they sell that is hydrated-lime.
> Anyway, i took out the whiting and added this stuff and it definitely
helps
> the color response, although in some pieces there were more pinholes than
> usual.
> Does anyone know why this may help the color develop better? I know there
> must be some iron in it that could help but i don't know if that accounts
> for all the difference. Also, can anyone advise how to adjust the formula
> to limit the pinholes should i decide to go with this new recipe? Any
advice
> is appreciated. Here is the original recipe again:
> Dolomite 15.8
> custer spar 30.0
> whiting 11.1
> epk 16.8
> flint 26.3
> rutile 8
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