[Clayart] fast firing

paul gerhold gerholdclay at gmail.com
Thu Feb 25 18:38:02 UTC 2021

First you are baffled as to why I would say kinetic equilibrium is not a scientific explanation ( for glaze maturity) and then you say no glaze reaches kinetic equilibrium. An obvious contradiction when it comes to defining what constitutes a mature glaze. Also I question why you think a glaze cannot reach thermal equilibrium. Seems to me if you hold the same temp in a kiln for long enough the glaze will reach the same temp. As the gasses next to it. 

Also we are talking about if the same glaze fired at different rates of energy input to the same cone will look significantly different. Glaze composition is irrelevant since we are talking firing effects on the same glaze not on different glazes. And I do agree if you are firing for crystals there could be a difference although I have never seen any experimental results. Also saturated metal glazes do change with firing rate but I suggest they are a unique case. 

And you can stop repeating your lecture on cones since I along with almost any serious potter knows that the cone will bend at different end temps if the rate of energy input changes.  

Now back to my original question about the definition of a mature glaze as potters use the term. 

Sent from my iPad

> On Feb 25, 2021, at 1:14 PM, Robert Harris <robertgharris at gmail.com> wrote:
> I'm baffled why you think that an explanation that invokes kinetic
> equilibrium is not a scientific explanation. Simply firing hotter is not
> always a substitute for firing longer., and it will differ according to the
> makeup of the glass, and to an extent, how finely the particles are
> divided.
> Brass tacks: Essentially no glaze reaches kinetic or thermodynamic
> equilibrium (volcanoes are probably the only things that do), therefore the
> assumption that the substitution required of temperature for time is
> identical across all formulae is a non-starter.
> To expand further, Orton Cone 10 reaches a maximum temperature of 2284F if
> fired at 27F/hr (for the last 180F), 2345F @108F/hr and 2381 at 270F/hr. So
> for the exact formula of that cone you can see that firing from 2100F to
> top temperature (approx 180F from the top of the lowest temp), will take
> 6.8 hrs, for the second, 1.3hrs and for the third just 1 hrs (despite the
> significant rise in temp required). (And a cone 10 cone does not get
> anywhere near the sort of melting required for a true glaze).
> So if we take the middle temperature 2345-2284=61F. So we can basically
> extrapolate and say that for that specific recipe 5 hours of firing time
> can be replaced by an extra 61F of temperature. To assume that ALL (cone
> 10) glaze recipes can have their reaction time cut by the same amount, by
> the same increase in temperature is ludicrous. Just think about how
> particle size (especially silica) affects glazes. Then add in the effects
> of low-temperature fluxes such as boron, or the difference in melting
> temperature between Nepheline Syenite and Custer, and it is easy to see
> that a series of glazes that do not reach kinetic equilibrium is going to
> require different temperature increases to make up for time, and they are
> all going to be different from our standard (the Orton Cone series).
> Is that sufficiently scientific? Where do you see the holes?
> Robert
>> On Wed, 24 Feb 2021 at 20:29, paul gerhold <gerholdclay at gmail.com> wrote:
>> I have a degree in Chemical Engineering which is irrelevant to my question
>> on defining glaze maturation which so far nobody has given a science type
>> answer. And of course every glaze performs differently at a specific cone.
>> The question asked is there a significant difference in a glaze if it
>> reached the same at different rates of firing?
>> Sent from my iPad
>>> On Feb 24, 2021, at 3:29 PM, Robert Harris <robertgharris at gmail.com>
>> wrote:
>>> 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
>>> difference.
>>>> 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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