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Firing Schedule Madness


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#1 docweathers

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Posted 10 February 2014 - 12:54 PM

it seems like unique firing schedules are in fashion this season. Every time I find a new glazes I want to try it has a different firing schedule than anything else I've dealt with. Since I have a fairly large kiln, Skutt 1227, it is unlikely that I would want to fill it kiln with pots all having the same glaze. On the other hand I'm not really excited about firing it was just a few pots in it.

 

Is anyone else frustrated by this?

Have you found a way of coping with this besides avoiding glazes that have unique firing schedules?


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#2 Pres

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Posted 10 February 2014 - 01:19 PM

I used to use commercial glazes from suppliers years ago, specifically Minnesota and ART. While these glazes were beautiful, they all had their quirks. Some would run if applied to the bottom areas or were over ^6, others would not develop color unless they were closer to ^6.5. In the end it was a matter of knowing the kiln, and knowing the glazes.  But then we did not have the programmable controlling that we have today, or some of us have. If you know your kiln, and know what the requirements of the glaze is, I would think you could extrapolate the type of firing that would best fit for multiple glaze needs. It may take a little tweeking, but in the end should work.


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#3 Norm Stuart

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Posted 10 February 2014 - 02:19 PM

We add a slow-cool onto our Cone 6 firing which develops the sort of crystallized look typically created by a hard fire brick kiln, but many glazes designed for a free-fall cooling in an electric cone become quite ugly.

 

Reformulating all of our glazes to be compatible with this firing took intuition and a lot of work.  Ultimately, it typically required the addition of 10% to 20% of a very fluxed frit like Ferro 3269 which adds additional glass and flux, so the the crystal formation remains below a coating of glass.

 

Now we're trying to generically add macro-crystalline glazes to our regular firing without upsetting the results of other glazes.  So I took our six hour slow-cool firing which free-falls from Cone 6 to 1,800 F and declines by 50 F per hour until 1,500 - and made two minor changes.

 

I've been told zinc silicate forms especially between 1,850 and 1,800.  So I am now starting the slow-cool at 1,850 and have added a 30 minute hold at 1,800.  So I'm adding an extra 1.5 hours of partial heating at a higher temperature range where in my experience I've seen little crystallization of other glaze melt materials.

 

One of the choices I made in this studio was purchasing a highly powered but small 36 watt a smaller 3.5 cubic foot kiln.  To keep up with our supply of ware we fire an average of 186 times a year - and our studio is only officially open Saturday, Sunday and Monday. 

 

What this means, apart from replacing heating elements and relays every 14 months, is that we have a very quick turn-around time for artists and don't mind placing one or two items in a fast gilding fire.  It also means I can break down the firings into an occasional Cone 6 firing without a slow-cool if someone wants to use certain commercial glazes which don't look well in a slow-cool.

 

A larger kiln would have been modestly more energy efficient, with lower maintenance costs, but only if it was equally filled which would have meant long waits to get your ware fired.   I also could have fired large pieces - my landing duck sculpture could have had its wings fully extended, instead of being caught in the act of folding his wings.  But I'd still make the same choice of kiln.

 

We have a couple of people who have spent a lot of time using complex macro-crystalline firings, but they do these at home in their own kilns.  I'm hoping for a fairly significant coverage of macrocrystalline formation with my minor modification.  I can't envision using more complex firings to create different patterns of crystals unless we have a large demand for it.



#4 neilestrick

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Posted 10 February 2014 - 03:15 PM

I always use the same firing schedule- Cone Fire mode to cone 6 with an added cooling cycle of 175F/hr to 1500. If a glaze doesn't work on that schedule then I either tweak the glaze or don't use it. Its a waste of my time and energy to have to fire more than one way, and impossible for my students to keep track of which glazes they used on which pots. Everything goes into the same kiln at the same time. No headaches. If my students bring in commercial glazes, they figure out how to use them in that firing schedule, whether its applying them thinner or thicker or whatever. Plus it's not nearly as time and cost effective to fire my small kiln half a dozen times instead of firing the big kiln once.

Mastering Cone 6 Glazes, an excellent book, seems to have convinced everyone that they need a custom firing schedule, when in reality most glazes work just fine with a regular ol' Cone Fire mode firing. But in some cases an added controlled cooling can improve the look of your glazes, so that's definitely worth exploring. Only about half of the 15 glazes in my studio benefit greatly from the cooling cycle, while for the rest the difference is minor.

Pick a firing schedule that works for most of your glazes, then adjust the other glazes to work with it. If a glaze really needs a different schedule, you'll have to decide if it's worth the effort to accommodate it.
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#5 ayjay

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Posted 11 February 2014 - 06:04 AM

it seems like unique firing schedules are in fashion this season. Every time I find a new glazes I want to try it has a different firing schedule than anything else I've dealt with. Since I have a fairly large kiln, Skutt 1227, it is unlikely that I would want to fill it kiln with pots all having the same glaze. On the other hand I'm not really excited about firing it was just a few pots in it.

 

Is anyone else frustrated by this?

Have you found a way of coping with this besides avoiding glazes that have unique firing schedules?

I know exactly what you mean: I don't have the amount of production which allows extensive testing on a sensible time scale, so I do use published glaze recipes and sometimes change them a little to suit my purposes (sometimes I even convince myself I know what I'm doing).

 

 I just remain grateful for those published recipes which someone has probably worked hard on and decided to share with the wider community, they don't have to share, any many don't, if they don't fit my simple firing schedule I usually try them as is the first time and if they don't work for me they get tweaked once or twice and then abandoned if they still don't work - there's plenty of good glazes that do - how many do you really need?

 

I'm reaching the stage where I want to have a half dozen glazes that I know will work, can interact positively with each other and maybe test a new glaze with each firing, hoping for one of those spectacular results, (I've managed acceptable so far, still waiting for spectacular).

 

Here's my most recent favourite, not spectacular by any means, but I rather like it (and I need to sort out the lighting for pottery pics).

 

Attached File  DSCF1714 _C-R.jpg   439.52KB   9 downloads



#6 Norm Stuart

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Posted 11 February 2014 - 07:30 AM

I've found only two widely popular glazes designed for a rapid free-fall in temperature after a Cone-fire to ^6 in an electric kiln, which I've not been able to reformulate to our six hour slow-cool between 1,800 and 1,500 F.

 

The first is Laguna Tang Lime Crackle, a combination of Ferro Frit 3269, 1/2% Chrome Oxide, and some silica.  Instead of crazing with a clear lime glass, it becomes and uncrazed mustard color when cooled very slowly - as the slow-cooling fixes the glaze-fir problem designed into this glaze.

 

The second widely used glaze are the many variations of Blue Hare's fur glaze.   The rutile in this Nepheleine Syenite doesn't leave hair-like trails in the nepheleine glass melt, but becomes a uniform blue color, regardless of the recipe tried.  In general Nepheleine Syenite heavy recipes need a different flux for slow-cooling as the high Alumina content of this material tends to provide a sold coloration when given enough time to react and crystallize.

 

Enough time has passed that no one at our studio even remembers these glazes, which is fine, but reformulating them is still a goal of mine.

 

Our studio members voted that they preferred the slowest-cool program we tried out rather than the faster slow-cool suggested by the book "Mastering Cone 6 Glazes".

 

In general with very slow cooling you end up with a more sophisticated cone 10 style look without the bright glassy "poster paint" look typical of many Cone 6 glazes in free-fall cooling.

 

These two glazes below illustrate the sort of difference very slow-cooling has on some glazes.   I much prefer Randy McCalls Warm Jade slow-cooled to the original.  I needed to add 10% extra frit to develop  a nice glaze from Clear Blue which becomes over-crystalllized.  Some people prefer the more crystallized look of a slow-cool, while others dislike it.

 

The consensus at our studio is members like the look of the very slow-cooled glazed.

med_gallery_18533_643_16126.jpg

 

med_gallery_18533_643_708585.jpg

 

The difference in look between fast-cooled and slow-cooled is quite distinctive.  Which look you want for your ware is an entirely personal choice.  As with the last glaze shown, over-crystallization has to be dealt with by adjusting the glaze recipe.

 

We add a slow-cool onto our Cone 6 firing which develops the sort of crystallized look typically created by a hard fire brick kiln, but many glazes designed for a free-fall cooling in an electric cone become quite ugly.

 

Reformulating all of our glazes to be compatible with this firing took intuition and a lot of work.  Ultimately, it typically required the addition of 10% to 20% of a very fluxed frit like Ferro 3269 which adds additional glass and flux, so the the crystal formation remains below a coating of glass.

 

Now we're trying to generically add macro-crystalline glazes to our regular firing without upsetting the results of other glazes.  So I took our six hour slow-cool firing which free-falls from Cone 6 to 1,800 F and declines by 50 F per hour until 1,500 - and made two minor changes.

 

I've been told zinc silicate forms especially between 1,850 and 1,800.  So I am now starting the slow-cool at 1,850 and have added a 30 minute hold at 1,800.  So I'm adding an extra 1.5 hours of partial heating at a higher temperature range where in my experience I've seen little crystallization of other glaze melt materials.

 

One of the choices I made in this studio was purchasing a highly powered but small 36 watt a smaller 3.5 cubic foot kiln.  To keep up with our supply of ware we fire an average of 186 times a year - and our studio is only officially open Saturday, Sunday and Monday. 

 

What this means, apart from replacing heating elements and relays every 14 months, is that we have a very quick turn-around time for artists and don't mind placing one or two items in a fast gilding fire.  It also means I can break down the firings into an occasional Cone 6 firing without a slow-cool if someone wants to use certain commercial glazes which don't look well in a slow-cool.

 

A larger kiln would have been modestly more energy efficient, with lower maintenance costs, but only if it was equally filled which would have meant long waits to get your ware fired.   I also could have fired large pieces - my landing duck sculpture could have had its wings fully extended, instead of being caught in the act of folding his wings.  But I'd still make the same choice of kiln.

 

We have a couple of people who have spent a lot of time using complex macro-crystalline firings, but they do these at home in their own kilns.  I'm hoping for a fairly significant coverage of macrocrystalline formation with my minor modification.  I can't envision using more complex firings to create different patterns of crystals unless we have a large demand for it.



#7 docweathers

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Posted 11 February 2014 - 01:25 PM

 

it seems like unique firing schedules are in fashion this season. Every time I find a new glazes I want to try it has a different firing schedule than anything else I've dealt with. Since I have a fairly large kiln, Skutt 1227, it is unlikely that I would want to fill it kiln with pots all having the same glaze. On the other hand I'm not really excited about firing it was just a few pots in it.

 

Is anyone else frustrated by this?

Have you found a way of coping with this besides avoiding glazes that have unique firing schedules?

I know exactly what you mean: I don't have the amount of production which allows extensive testing on a sensible time scale, so I do use published glaze recipes and sometimes change them a little to suit my purposes (sometimes I even convince myself I know what I'm doing).

 

 I just remain grateful for those published recipes which someone has probably worked hard on and decided to share with the wider community, they don't have to share, any many don't, if they don't fit my simple firing schedule I usually try them as is the first time and if they don't work for me they get tweaked once or twice and then abandoned if they still don't work - there's plenty of good glazes that do - how many do you really need?

 

I'm reaching the stage where I want to have a half dozen glazes that I know will work, can interact positively with each other and maybe test a new glaze with each firing, hoping for one of those spectacular results, (I've managed acceptable so far, still waiting for spectacular).

 

Here's my most recent favourite, not spectacular by any means, but I rather like it (and I need to sort out the lighting for pottery pics).

 

attachicon.gifDSCF1714 _C-R.jpg

 

I like it too. What is it? what clay? What firing schedule


Larry

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#8 neilestrick

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Posted 11 February 2014 - 01:43 PM

The main reason I started doing a controlled cooling cycle was to even out the results from kiln to kiln. I've got 1 cu/ft, 3.5 cu/ft, and 21 cu/ft kilns. Cooling times in them vary by as much as 24 hours, which drastically screws up the results. By adding the cooling cycle everything looks the same, regardless of which kiln it was fired in.


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#9 Pres

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Posted 11 February 2014 - 05:01 PM

Excellent thought Neil. I have been firing an all manual for years and have always used a cool down. I do most of mine by heat color but not nearly as consistent as today's kiln controllers.


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#10 ayjay

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Posted 11 February 2014 - 05:20 PM

 

I like it too. What is it? what clay? What firing schedule

 

Thanks doc: It's just a small pot, the basic buff stoneware that we use at college, some torn newspaper strips applied as a resist while still on the wheel and then sodium silicate applied and dried with a heat gun and then ribbed out a little - bisque fired to ^05 then a wash of Iron Oxide, FF3110 and China clay applied to the cracks - (surplus sanded off the high spots) and a glaze of Jen's Juicy fruit with Liquorice on the rim - my glaze firing schedule is very simple - 100°C per hour to 1100°C and then @ 75°C per hour to 1200°C and a 20 minute soak - and then allowed to cool naturally.



#11 docweathers

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Posted 11 February 2014 - 10:43 PM

thanks I'll give it a try.


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