Paul on mon 20 jan 03
Hello,
I have found some evidence that suggests rutile blues do better with faster
cooling kilns. The same glaze i fired in a 40-50 cubic foot kiln very nicely
will come out white now in my 80-90 cubic foot kiln, both under heavy and
moderate reduction. I have seen the same recipe in several fiber kilns
coming out a nice, even dark, blue. And the best rutile blue i ever fired,
using the same recipe, was in a skutt 1227 kiln converted to gas, with two
burners coming in the bottom. It was a perfect, variegated blue with a very
glossy surface. I posted a question about rutile blues a few months ago and
got many responses, but still the same results in my kiln.
So before i phase out this glaze once and for all (replacing it with copper
reds which give me no trouble at all with this forced-air kiln) i want to
try to speed up the cooling one time to see if this does indeed have an
effect.
So does anyone have some suggestions on how to SAFELY speed up the cooling
cycle in a large IFB kiln? And at what temperature would the cooling cycle
become less influential of a factor?
One well-known potter mentioned that he cools quickly at a certain point to
"avoid any crystallization of titanium," (and this person said he has been
making his living with rutile blues for 30+ years but still finds it
mysterious) so i think he means that the formation of micro-crystals at a
certain period of the cooling cycle are not good for this type of glaze,
since they are a charactoristic of opaque and matt glazes. And it is true
that it comes out a pasty, opaque white for me.
I would think to leave the blowers on and everything open, but i do not know
the extent to which this can be done safely so i would like to hear some
suggestions. If it would help anyone answer these questions, i will post the
recipe (although i have tried several and none of them work). I fire to cone
11 and my kiln has about a two-cone differential.
RUTILE BLUE
DOLOMITE 15.8
CUSTER 30
WHITING 11.1
EPK 16.8
FLINT 26.3
RUTILE 8.0
Thanks!
Paul B
Snail Scott on tue 21 jan 03
At 06:49 PM 1/20/03 -0500, you wrote:
>So does anyone have some suggestions on how to SAFELY speed up the cooling
>cycle in a large IFB kiln?
>I would think to leave the blowers on and everything open, but i do not know
>the extent to which this can be done safely so i would like to hear some
>suggestions.
I've always functioned on the assumption that
crash-cooling in the high-temperature end of
the cycle is pretty safe - everything is still
'squishy'. It's in the lower half of cooling
that you have to be more careful, IMHO.
-Snail
Ron Roy on thu 23 jan 03
Hi Paul,
The first part has to do with knowing were the cooler spots in your kiln
are - part of the reason they may appear cooler is because they cool
faster. Best to try and find that out first.
If you have holes that your can insert a pyrometer - in different parts of
your kiln - you will have a much better idea of how to fast cool without
damaging your ware, kiln and furniture.
Kilns usually cool very fast when first shut off - it depends on how your
kiln is constructed - fiber kilns cool very fast compared to soft brick
kilns - hard brick kilns cool slow.
Hi fire glazes are usually frozen (not pyro plastic anymore) between 600
and 800C - if you fast cool (leave your damper open after a short slow cool
just below top temp) down to 800 C that should ensure there will not be
enough time for crystals to form in most glazes. The trick is to know what
part of your kiln cools the fastest - and stop the cooling using the
temperature there. Put your Rutile Blues in that area.
If you crash cool - in any part of your kiln - past the quartz inversion at
573C get ready to make a trip to the dump. Some glaze/clay combinations
will do OK but others may not - and furniture and bricks just hate going
through the inversion quick.
Let us know what happened when you figure it out.
RR
>I have found some evidence that suggests rutile blues do better with faster
>cooling kilns. The same glaze i fired in a 40-50 cubic foot kiln very nicely
>will come out white now in my 80-90 cubic foot kiln, both under heavy and
>moderate reduction. I have seen the same recipe in several fiber kilns
>coming out a nice, even dark, blue. And the best rutile blue i ever fired,
>using the same recipe, was in a skutt 1227 kiln converted to gas, with two
>burners coming in the bottom. It was a perfect, variegated blue with a very
>glossy surface. I posted a question about rutile blues a few months ago and
>got many responses, but still the same results in my kiln.
>So before i phase out this glaze once and for all (replacing it with copper
>reds which give me no trouble at all with this forced-air kiln) i want to
>try to speed up the cooling one time to see if this does indeed have an
>effect.
>So does anyone have some suggestions on how to SAFELY speed up the cooling
>cycle in a large IFB kiln? And at what temperature would the cooling cycle
>become less influential of a factor?
>One well-known potter mentioned that he cools quickly at a certain point to
>"avoid any crystallization of titanium," (and this person said he has been
>making his living with rutile blues for 30+ years but still finds it
>mysterious) so i think he means that the formation of micro-crystals at a
>certain period of the cooling cycle are not good for this type of glaze,
>since they are a charactoristic of opaque and matt glazes. And it is true
>that it comes out a pasty, opaque white for me.
>I would think to leave the blowers on and everything open, but i do not know
>the extent to which this can be done safely so i would like to hear some
>suggestions. If it would help anyone answer these questions, i will post the
>recipe (although i have tried several and none of them work). I fire to cone
>11 and my kiln has about a two-cone differential.
>
>RUTILE BLUE
>DOLOMITE 15.8
>CUSTER 30
>WHITING 11.1
>EPK 16.8
>FLINT 26.3
>RUTILE 8.0
>
>Thanks!
>Paul B
>
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Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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