[Clayart] fast firing

Robert Harris robertgharris at gmail.com
Wed Feb 24 17:14:38 UTC 2021

Paul, think like a chemist! This one is easy. Reaction kinetics.  This is a
pretty good example of thermodynamic versus kinetic equilibrium.
You are assuming that silica glass melting/mixing/reaction is identical
across glaze recipes and (and cone recipes) such that temperature can be
linearly substituted with time. In other words, a cone recipe has a
particular relationship between time and temperature, increase the time and
you substitute for temperature. However, not all glazes will show the same
substitution. Also, higher temperatures will affect viscosity and boiling
point in a way that is not substitutable for time.
In terms of observed experience, those glazes that are very well melted at
higher the top of their cone range, and have a wide range of acceptable
temperatures, are unlikely to have much visual difference. I bet that other
measures such as clay/glaze bonding, durability etc show more of a

On Wed, 24 Feb 2021 at 08:30, paul gerhold <gerholdclay at gmail.com> wrote:

> Maybe the issue is the definition of glaze maturation. My guess is it only
> means the glaze satisfy the potters  goals for the glaze.
> Personally I cannot sayI have ever seen any difference in my glazes
> whether I get to the cone slowly or rapidly. My assumption would be the
> only way it would make any difference is if there is a significant lag time
> for the energy in the kiln to transfer into the glaze.   I wonder if anyone
> has any actual evidence of difference.
> Paul
> Sent from my iPad
> > On Feb 23, 2021, at 4:13 PM, vpitelka at dtccom.net wrote:
> >
> > Hi Paul -
> > This has been pretty thoroughly discussed many times on Clayart.
> Initially, you can increase temperature very quickly, but it is natural
> that a kiln will slow down as it approaches maturation temperature, and
> that gives time for heatwork to do its job on the glazes.  If you fire
> right up to intended maturation temperature according to a cone or the
> setting on a programmable kiln and then hold for a period of time to mature
> the glazes, you will be overfiring.  Maturation is a result of both
> temperature and duration.  If you slow down the firing at the end as you
> work up to maturation temperature, you can hit the cone dead-on while also
> having allowed the glazes to mature.  That said, if you did some
> experimentation, fast-firing to a maturation temperature perhaps a cone
> lower than what you intend, and then holding the temperature for a period
> of time, you could probably get the same results, but why do that?
> > - Vince
> >
> > Vince Pitelka
> > Professor Emeritus of Art/Ceramics
> > Appalachian Center for Craft
> > School of Art, Craft & Design
> > Tennessee Tech University
> > Now Residing Chapel Hill, NC
> > vpitelka at dtccom.net
> > www.vincepitelka.com
> >
> > -----Original Message-----
> > From: Clayart <clayart-bounces at lists.clayartworld.com> On Behalf Of
> paul gerhold
> > Sent: Tuesday, February 23, 2021 12:19 PM
> > To: Clayart international pottery discussion forum <
> clayart at lists.clayartworld.com>
> > Subject: Re: [Clayart] fast firing
> >
> > Vince,
> > I do not understand how glaze maturation can change from fast to slow
> firing if you are firing to the same cone. Obviously if you are firing to
> the same end temp. Getting there slower will increase the heat work, as
> will holding at peak temp.
> >
> > Paul
> >
> > Sent from my iPad
> >
> >> On Feb 22, 2021, at 9:39 PM, vpitelka at dtccom.net wrote:
> >>
> >> The main thing that suffers in excessively-fast glaze firings is glaze
> maturation.  When I was making kitchenware and tableware full-time in
> Northern California 1975-85, I built a 100-cubic-foot natural gas, natural
> draft downdraft car kiln.  The decoration was mostly oxide brushwork, slip
> decoration, and impressed decoration with a few transparent glazes and
> simple colored glazes, rather than the subtleties of glaze outcome.  I did
> want even reduction, but never had trouble achieving that.  You can see the
> kiln and the wares in the Railroad Stoneware section of the gallery on my
> website if you care to.  When I was rushed, as it seems I always was before
> our big annual studio sale in early December, I would fire that
> 100-cubic-foot kiln on an 18-hour cycle - seven hours from cold to cone-10,
> seven hours to cool, and four hours to unload and reload.  The time of day
> would cease to matter, and I'd do four or five firings in sequence on that
> 18-hour schedule to get ready for the studio sale, fitting in a little
> sleep here and there as I was able.  I was happy with the results.
> >>
> >> Periodically during my years at the Appalachian Center for Craft, I'd
> have a student proudly proclaim that they had fired our 40-cubic-foot
> downdraft kiln from cold to cone-10 in four hours.  Yeah, they did, but the
> results were almost always lackluster.  In any firing, the hotter the kiln
> gets, the more BTUs it takes to advance it further.  So, if you keep the
> heat settings constant in the latter part of the firing, temperature rises
> slows down, and heatwork has time to mature the glazes.  In contrast, if
> you keep cranking up the BTUs in the latter part of the firing to get done
> in a hurry, the temperature zooms ahead of maturation, and you end up with
> a lot of dead, lifeless glazes.
> >>
> >> In some tile factories, the tiles moving through giant rolling-hearth
> kilns pass from room temperature to cone-10 and back to room temperature in
> as little as thirty minutes.
> >> - Vince
> >>
> >> Vince Pitelka
> >> Professor Emeritus of Art/Ceramics
> >> Appalachian Center for Craft
> >> School of Art, Craft & Design
> >> Tennessee Tech University
> >> Now Residing Chapel Hill, NC
> >> vpitelka at dtccom.net
> >> www.vincepitelka.com
> >>
> >> -----Original Message-----
> >> From: Clayart <clayart-bounces at lists.clayartworld.com> On Behalf Of
> >> Daphne Vega
> >> Sent: Monday, February 22, 2021 5:56 PM
> >> To: Clayart international pottery discussion forum
> >> <clayart at lists.clayartworld.com>
> >> Subject: Re: [Clayart] fast firing
> >>
> >> Hi Mel
> >> I’m curious, when glaze firing, what is ‘too fast’? Is it even a
> problem at all if the emphasis is on the slow cool down, and reducing on
> the cool down?
> >> You know (as I posted here a few times) I was struggling with evening
> out my kiln in 18/19, firing it over and over with nothing but bricks
> inside to experiment with different modifications to the control. Well I
> learned how to drive it pretty well and then the last 2 firings last year
> (moved studio and haven’t fired in it since) I realized it was moving so
> fast that I was going to potentially get it to cone 6 in under 4 hours. I
> got nervous so I slowed it down to stretch the firing out a bit longer,
> because it was filled with pieces I could not afford to lose and I did not
> know what I would get with such a different fire schedule.
> >> I remrmber in college being told that there was definitely a too fast,
> but I didn’t question how or why then.
> >> I know the best answer is to test myself ;)
> >>
> >> Still, I’d love to hear others thoughts and experiences
> >>
> >> Thanks.
> >> Daphne
> >>
> >> Autocorrect may win the battle but not the where.
> >>
> >>>> On Feb 22, 2021, at 1:02 PM, mel jacobson <melpots at mail.com> wrote:
> >>>
> >>> since i do it all the time, some observations.
> >>> i took the controller off my small kiln.
> >>> i use a tested and trusted clay and glaze.
> >>> i down fire after shutting off the kiln.
> >>> my gas kilns are all manual. they fire like rocket ships.
> >>>
> >>> kiln controllers for most of you are miracles. busy schedule, fire
> >>> while at the movie, fire with your smart phone..nice. but the
> >>> programs are made by others, for a broad range of people firing. so,
> one size fits all.
> >>> and for many, re/program is not easy.  and i hate the kiln shutting
> down at 2000 with a note:
> >>> "you are a naughty potter, ach tung, start again." "heilorton"
> >>>
> >>> i do not live in that camp. size 32 shorts do not fit me.
> >>> i will make up my own mind thank you.  and, i never leave my kilns
> while firing.
> >>>
> >>> bill schran when making crystals needs the controller and controls it.
> it is a god send.
> >>> but i have a nice controller on my big electric, it is great for
> bisque. slow mode.
> >>> rarely glaze fire in it.  Colleen fired about 60 mugs last week in
> >>> the big kiln to cone 7.  fired great.  because of -30 in the kiln
> >>> room, she unhooked the controller, and plugged the kiln directly into
> the wall outlet. fired with the kiln sitter.  you see, dual system.
> >>>
> >>> i bisque fire very slow, and allow gobs of time for the clay to expel
> >>> all gases.  and, some commercial bodies always bloat if not slow
> >>> bisque fired.  lots of crap in that clay.
> >>>
> >>> but, if you have a controller and love it, yes by all means enjoy it
> >>> and be thankful for it. it is yours, learn to control it however.
> >>> mel
> >>>
> >>>
> >>>
> >>> website: www.melpots.com
> >>> www.melpots.com/CLAYART.HTML
> >>>
> >>
> >>
> >
> >
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