Ian Currie on fri 5 jan 01
Greetings
I missed the earlier discussion on length of firing, but I am in substantial
agreement with Hank (and Chris?) I've added some thoughts below this quote:
>I fire to cone 11 in about 12 to 13 hr. It's always been my belief that
>anything faster will not give your glaze time to ripen. My old glaze
teacher
>always told us no faster then 265*f per. hr. that's about what I do, the
>slow going in the start of the firing when your driving off the H2o can
make
>the firing seem longer but its really not. Chris
I have been surprized over years of conducting glaze workshops of the lack
of understanding about the importance of speed of firing, and cooling speed.
I thought we all knew?? It seems that commercial kiln designers are
assuming we want to have as little to do with the firing as possible. They
have things like kiln sitters, which I would personally think twice about
using even for a bisque firing... and cut-offs that provide no "soak"
period... and as for firing down... why would we bother??? OK, so some
glazes do work best in a fast cooling... but the work I've done indicates
fairly clearly that fast-firing and fast-cooling will restrict the range of
results available to us.... and will prevent some qualities appearing. [I
do appreciate that some people have no option but to use inadequate
automatic stuff.... but I'd like to point out some of the tradeoffs.]
There was a belief some years ago that any glaze that could be achieved with
a slow firing could be done with a fast firing if one was willing to adjust
the glaze properly. I don't think this is a useful theory.... Sometimes we
may find an example that confirms the idea, but there are many things that
simply take time in the firing, especially at top temperature and in the
cooling cycle:
Depending on the particle size, your glaze may need more time at top
temperature to melt properly. This can affect things like the glaze surface
quality including mattness and feel, pinholes and bubbles, opacity and
opalescence, subsequent crystal development in some glazes that use the
unmelted "seeds" as crystal seeding points....
Some glaze qualities require a long underfiring. Steve Harrison has
achieved wonderful classical kuan and celadon glazes by a combination of
lower firing temperature and held for a longer time... this combined with a
little ball milling. The thick applications he uses would simply flow off
at a higher firing temperature. In some cases he has lowered maturing
temperature by as much as 100 degrees C (over 200 F)! ... without changing
the glaze recipe.
If the glaze (stoneware or mid-fire) has some colour-break (colour changing
sharply from one to another depending on thickness) this often depends on
the development on the clay-glaze interface zone at high temperature... and
this develops more as the top temperature is held longer.... So the longer
firing is going to give more of the interface colour. To some extent we can
compensate for short firing time by firing higher... but this changes other
things.... you poke it in here it jumps out over there!
The cooling cycle is quite important as this period determines the
occurrence, size, frequency and type of crystals in the glaze. Many of the
crystal effects that we are firing for actually occur well down in the
cooling cycle, and the crystals grow larger the longer the time spent at the
appropriate temperature.... So the rate of cooling is going to affect
microcrystal mattness.... or the size of macro crystals in for example a
zinc
crystal glaze.... or whether a glaze has spotty crystals (like a 'teadust")
or
all-over matt...
So... if you want to increase the possibilities several fold, consider more
than fast firing and fast cooling!
And for my friends who have been cheering along my big clean-up, you will be
glad to know that sections of my desk top appeared yesterday, and most of
the floor boards are now visible! Entropy currently cowering in the corner
will no doubt begin the inexorable creep-back as soon as my back is
turned... but one is almost in charge here... for the present!
Millennial greetings to all
Ian Currie
P.S. If you would like to know more about my glaze method workshops, or if
you would like to purchase one of my books, go to:
http://ian.currie.to/
or just e-mail me. If you pay for the books by credit card at my web site,
they usually take about a week to arrive.
Incidentally, the value of Australian currency is currently way down, so the
book price to you is also down. All prices quoted at my website are in
Aussie dollars.
Paul Taylor on sun 7 jan 01
Dear Ian
I agree totally with your post . The kiln technology we purchase and
build comes with an industrial agenda - cost and turnover.
If you want to get the many effects that distinguishes hand made from
industry an industrial designed kiln will not do.
Adding a seed like tin oxide or titanium will give some interesting
substitute effects. If you are happy with these or using a clear glaze over
stains or slips the modern kiln will do.
I also wonder if a short firing has to be very well managed and very even
firing to get even these effects I believe that the short firing give very
narrow windows of opportunity for managing carbon and oxygen, reduction, and
cooling.
I am amazed to hear someone is doing parallel work to me in the celadon
field and has come to the same conclusions
I would dearly like to see some examples of his work I have not got the
colors working as well as I would like . There are so many people who make
watery greens and call them celadons and their over blown reputations or
socio ceramic positions let hem get away with it. I tend not to be curious
of their celadon recipes - but now I am - this Steve Harrison sounds like he
is worth a bother.
Regards from Paul Taylor
http://www.anu.ie/westportpottery
> From: Ian Currie
> Reply-To: Ceramic Arts Discussion List
> Date: Fri, 5 Jan 2001 16:20:45 -0500
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Length of Firing and Cooling
>
> Greetings
>
> I missed the earlier discussion on length of firing, but I am in substantial
> agreement with Hank (and Chris?) I've added some thoughts below this quote:
>
>> I fire to cone 11 in about 12 to 13 hr. It's always been my belief that
>> anything faster will not give your glaze time to ripen. My old glaze
> teacher
>> always told us no faster then 265*f per. hr. that's about what I do, the
>> slow going in the start of the firing when your driving off the H2o can
> make
>> the firing seem longer but its really not. Chris
>
> I have been surprized over years of conducting glaze workshops of the lack
> of understanding about the importance of speed of firing, and cooling speed.
> I thought we all knew?? It seems that commercial kiln designers are
> assuming we want to have as little to do with the firing as possible. They
> have things like kiln sitters, which I would personally think twice about
> using even for a bisque firing... and cut-offs that provide no "soak"
> period... and as for firing down... why would we bother??? OK, so some
> glazes do work best in a fast cooling... but the work I've done indicates
> fairly clearly that fast-firing and fast-cooling will restrict the range of
> results available to us.... and will prevent some qualities appearing. [I
> do appreciate that some people have no option but to use inadequate
> automatic stuff.... but I'd like to point out some of the tradeoffs.]
>
> There was a belief some years ago that any glaze that could be achieved with
> a slow firing could be done with a fast firing if one was willing to adjust
> the glaze properly. I don't think this is a useful theory.... Sometimes we
> may find an example that confirms the idea, but there are many things that
> simply take time in the firing, especially at top temperature and in the
> cooling cycle:
>
> Depending on the particle size, your glaze may need more time at top
> temperature to melt properly. This can affect things like the glaze surface
> quality including mattness and feel, pinholes and bubbles, opacity and
> opalescence, subsequent crystal development in some glazes that use the
> unmelted "seeds" as crystal seeding points....
>
> Some glaze qualities require a long underfiring. Steve Harrison has
> achieved wonderful classical kuan and celadon glazes by a combination of
> lower firing temperature and held for a longer time... this combined with a
> little ball milling. The thick applications he uses would simply flow off
> at a higher firing temperature. In some cases he has lowered maturing
> temperature by as much as 100 degrees C (over 200 F)! ... without changing
> the glaze recipe.
>
> If the glaze (stoneware or mid-fire) has some colour-break (colour changing
> sharply from one to another depending on thickness) this often depends on
> the development on the clay-glaze interface zone at high temperature... and
> this develops more as the top temperature is held longer.... So the longer
> firing is going to give more of the interface colour. To some extent we can
> compensate for short firing time by firing higher... but this changes other
> things.... you poke it in here it jumps out over there!
>
> The cooling cycle is quite important as this period determines the
> occurrence, size, frequency and type of crystals in the glaze. Many of the
> crystal effects that we are firing for actually occur well down in the
> cooling cycle, and the crystals grow larger the longer the time spent at the
> appropriate temperature.... So the rate of cooling is going to affect
> microcrystal mattness.... or the size of macro crystals in for example a
> zinc
> crystal glaze.... or whether a glaze has spotty crystals (like a 'teadust")
> or
> all-over matt...
>
> So... if you want to increase the possibilities several fold, consider more
> than fast firing and fast cooling!
>
> And for my friends who have been cheering along my big clean-up, you will be
> glad to know that sections of my desk top appeared yesterday, and most of
> the floor boards are now visible! Entropy currently cowering in the corner
> will no doubt begin the inexorable creep-back as soon as my back is
> turned... but one is almost in charge here... for the present!
>
> Millennial greetings to all
>
> Ian Currie
>
> P.S. If you would like to know more about my glaze method workshops, or if
> you would like to purchase one of my books, go to:
> http://ian.currie.to/
> or just e-mail me. If you pay for the books by credit card at my web site,
> they usually take about a week to arrive.
>
> Incidentally, the value of Australian currency is currently way down, so the
> book price to you is also down. All prices quoted at my website are in
> Aussie dollars.
Ian Currie on mon 8 jan 01
Hi Paul
Thanks for the response. Steve is definitely worth the bother! He is also
well known in Australia for his understanding of firing, kiln design, and
wood firing in particular.
I don't think he is on Clayart, but I've forwarded your Clayart post to him.
I'll get some references to his work to pass on.
Incidentally, I think this trend (of firing lower for some of the classical
Chinese glazes) can be traced back at least to Robert Tichane in his book
"Those Celadon Blues". Now retired, he was a glass technologist with
Corning.
Regards
Ian Currie
http://ian.currie.to/
> I am amazed to hear someone is doing parallel work to me in the celadon
>field and has come to the same conclusions
>
>I would dearly like to see some examples of his work I have not got the
>colors working as well as I would like . There are so many people who make
>watery greens and call them celadons and their over blown reputations or
>socio ceramic positions let hem get away with it. I tend not to be curious
>of their celadon recipes - but now I am - this Steve Harrison sounds like
he
>is worth a bother.
>
> Regards from Paul Taylor
>http://www.anu.ie/westportpottery
Khaimraj Seepersad on mon 8 jan 01
Ian Currie typed -
> Some glaze qualities require a long underfiring. Steve Harrison has
> achieved wonderful classical kuan and celadon glazes by a combination of
> lower firing temperature and held for a longer time... this combined with
a
> little ball milling. The thick applications he uses would simply flow off
> at a higher firing temperature. In some cases he has lowered maturing
> temperature by as much as 100 degrees C (over 200 F)! ... without changing
> the glaze recipe.
Good Day to All ,
Fascinating idea - runs well with the page 190 -
Ceramics for the Artist Potter - F.H . Norton .
10 minutes to 1225 deg.c
100 minutes to 1200 deg.c
1000 minutes to 1175 deg.c
Influence on time of maturing porcelain .
You can see this with marble sized pieces of frit
exposed to long soaks at 800 deg.c for 15 minutes
, 30 minutes , 45 minutes and so on .
Good situation to note -- old idea - new use .
Khaimraj
-----Original Message-----
From: Paul Taylor
>Dear Ian
snip
>I would dearly like to see some examples of his work I have not got the
>colors working as well as I would like . There are so many people who make
>watery greens and call them celadons and their over blown reputations or
>socio ceramic positions let hem get away with it. I tend not to be curious
>of their celadon recipes - but now I am - this Steve Harrison sounds like
he
>is worth a bother.
>
> Regards from Paul Taylor
>http://www.anu.ie/westportpottery
>
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