Connie Woodward on wed 22 jan 03
I came to close to the same conclusion, the tests I made where the
rutile glaze cooler faster was a more richer deeper blue.
But also it seemed firing to a full cone 11 helped develop the
color. It did seem like I got more crazing with the fast cool,
though. Shouldn't a glaze fit or not? maybe it just won't show
up for longer on my slow-cool pots?
a slow cool - once it got to a full cone 11, I drop the temp 100 degrees C
and held it there for an hour, yelded more of the whiter/beige frothy color.
Also when I really, really heavily reduced starting at 900 degrees
C up to cone 11 with a "dark" clay,
Armadillo Clay's Balcones Dark, I got some
really nice purples and blues with pink-ish blushes.
I am using the well-known Rutile Blue #2:
Dolomite 15.8
Custer feldspar 30
Whiting 11.1
EPK 16.8
Silica 26.3
Rutile 8
But I am happy! it may be "low artsy class" but I love blue!
Thanks,
Connie
============================================================
Connie Woodward Karattopp Pottery 713-256-5907
Navasota, TX www.karattopp.com connie@karattopp.com
> -----Original Message-----
> From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG]On Behalf Of Paul
> Sent: Wednesday, January 22, 2003 12:48 PM
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: FAST COOLING/RUTILE BLUE
>
>
> 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.
> 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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Paul on wed 22 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.
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
Craig Martell on thu 23 jan 03
Hi:
Without going into too much detail, I'll give my view on why a fast cool
may sometimes produce a better blue.
I looked at the last recipe that was posted and it contained enough
dolomite and whiting to generate a fair amount of crystal growth with a
slower cool. I have a strong opinion that rutile blue glazes produce the
blue thru optical effects rather than taking the rutile into solution and
producing color with pigmentation from the rutile. If we can look at
rutile blues as somewhat related to chuns, which are also optical, there
needs to be a certain amount of undisolved material such as silica and
perhaps a bit of crystal formation to refract light and produce an optical
blue. With a slower cool, we could expect that there would be too much
crystal growth causing more of an opaque scenario that would negate the
optical blue.
If you would like a very good explanation of the optical effects that
produce blue light, see Ian Currie's book Stoneware Glazes A Systematic
Approach and look in the section on Chun glazes.
That's it for me today. Time for a nice bottle of Fuller's ESB. If you
want my opinion, the best ales in the world are made in the UK. No doubt
about it!! As for music or what I listen to, it's time for Captain
Beefheart and his Magic Band!
Craig Martell Hopewell, Oregon
Dave Murphy on thu 23 jan 03
Paul:
I too used the same glaze for years getting great results in my fibre kiln.
When we built our IFB it came out more apricot and matted off white. Yuk!!
I discontinued it for awhile until crash cooling became the norm for shinos.
I tested the rutile blue to see if fast cooling was the solution for this
glaze. Bingo! It came out as varigated and lovely as before. Fast cooling
for us consists of firing to temp/cone 10 flat -15 min soak then crash
cool/blowers off/ to 1850 F then clam and cool as usual with damper closed
to 1000 F. Hope this helps.
Barbara Murphy
Waterloo County Pottery
David and Barbara Murphy
Waterloo Ontario
Canada
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