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changing kiln temperatures


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#1 asunta

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Posted 19 September 2012 - 08:23 AM

I've been trying Amacos Potters Choice glazes and have gotten o.k. results except for one called Ancient Jasper which is a combo of red and black. Mine comes out glossy brown. Not good. Contacted Amaco Tech help and was advised to alter my firing schedule down from the usual bisque firing of 11 hours to between 6 and 8 hours in order to achieve the results indicated on Amaco charts. This change seems radical to me, since I'm rather heavy-handed using a stoneware body. Is anyone else using these products? If so, would love to hear how you get the results advertised by Amaco, and how long you fire for.
Thanks, Asunta

#2 Pres

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Posted 19 September 2012 - 08:36 AM

I've been trying Amacos Potters Choice glazes and have gotten o.k. results except for one called Ancient Jasper which is a combo of red and black. Mine comes out glossy brown. Not good. Contacted Amaco Tech help and was advised to alter my firing schedule down from the usual bisque firing of 11 hours to between 6 and 8 hours in order to achieve the results indicated on Amaco charts. This change seems radical to me, since I'm rather heavy-handed using a stoneware body. Is anyone else using these products? If so, would love to hear how you get the results advertised by Amaco, and how long you fire for.
Thanks, Asunta


I had used Amaco glazes for years, and found in the long run that following their firing instructions gave me the best results no matter what glaze it was. Give it a try and see what heppens.

Simply retired teacher, not dead, living the dream. on and on and. . . . on. . . .                                                                                 http://picworkspottery.blogspot.com/


#3 Chris Campbell

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Posted 19 September 2012 - 02:17 PM

Asunta -
What do you mean by 'heavy handed using a stoneware body'?
I wonder because a six to eight hour bisque firing sounds about right.
Kiln heat work is the combination of time and temperature. Your longer firings could mean you have been reaching a higher cone temp than you realize. Do you use witness cones to check on what is happening in your bisque firings??

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#4 asunta

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Posted 19 September 2012 - 03:14 PM

Asunta -
What do you mean by 'heavy handed using a stoneware body'?
I wonder because a six to eight hour bisque firing sounds about right.
Kiln heat work is the combination of time and temperature. Your longer firings could mean you have been reaching a higher cone temp than you realize. Do you use witness cones to check on what is happening in your bisque firings??



#5 asunta

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Posted 19 September 2012 - 03:18 PM

Hi Chris
By heavy handed, I mean my ware is thick. And I misquoted my firing. It's not bisque, but the glaze firing. I usually fire about 11 hours. Haven't used cones, but depend on the kilns digital system. My greenware firing is about 8 hours. Isn't a 6 to 8 hour firing for a glaze batch cause for messing up the whole kiln load because it's so short a time?
thanks
Nancy

#6 Chris Campbell

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Posted 19 September 2012 - 03:53 PM

You cannot rely on your kiln's automatic system to tell you what happened inside. Theoretically the temperature was correct, but it was most likely higher and lower all over the kiln. The only way you will know what temp was reached on each shelf is to use 'witness cones'. The easiest and quickest to use (for me) are the self supporting Orton ones. If you are firing to Cone 6 you put in three cones on various shelves in your kiln ... the 5, 6, and 7. That way you will see how they bent and know exactly where your kiln fires hot and cool. If you have never tested before, put a set on every shelf.
One great reason to know this is you may want to place something special in a cool or hot spot to get better results.
You will also know if you need to tweek your firings ... if the whole kiln is only firing to Cone 5 when it should be 6 then you might need to replace some coils or the thermocouple.
If some shelves are bang on 6 but the top and bottom are 5 you might need to soak the load for 10 min at the high temp to even out the kiln.

Knowledge is power! :D Until you know if your kiln is firing correctly, you cannot judge your glaze results.

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#7 Mark C.

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Posted 19 September 2012 - 05:14 PM

(Haven't used cones, but depend on the kilns digital system.)



Take Chris's advice and put cones in as the above statement is a poor idea at best. Until you know what's going on (with cones) you are going to get results you cannot understand well.
Cones are cheap and you then will know what needs to be adjusted.
Mark
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#8 bciskepottery

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Posted 19 September 2012 - 08:51 PM

Here is a previous discussion on Ancient Jasper. http://ceramicartsda...__fromsearch__1




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