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Comparison Of Slow & Fast Cooled Iron Reds.


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#21 OffCenter

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Posted 27 June 2013 - 05:21 PM

Well ... I have had a hard time learning about firing and trying to understand the technical side and I thought I had a tentative grasp ( finally ) on what heat work was and how it affected firing results.
So when a potter with 34 years experience ... As John has ... Says these two firings had the same heatwork, it throws me back to square one of thinking I don't understand at all.


You probably understand as much or more than most of us. It's all more art than science and as Jesus said, "Heatwork is heatwork."

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#22 John255

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Posted 27 June 2013 - 05:28 PM



I have to comment here that the difference in the firings is a lot more than just the cooling rate.

Heatwork. The one hour hold took that firing way over Cone 6 to at least 7 or 8.
Holding at six doesn't mean the firing just sits at Cone 6 .... Firing temps are a combination of time and temp.
Think of holding your perfectly roasted chicken in the oven for an hour longer at 350 ... Different result ... no matter how you cool it.


We really didn't need the basic lecture on heat-work. The essential message of this thread is the quality and quantity of iron, for this batch of Baileys Red, had more visible red effect than soaking and slow cooling with approximately the same heat-work for both firings. This may be exciting news for folks with older kilns who have been told "Slow cooling is an absolute must, or the only way to get iron reds."
Regards,
John255


I swear I don't mean to be argumentative ... so please educate me because those two firings seem worlds apart to me. I cannot come close to understanding how the two could possibly have the same amount of heat work and I am not referring to basic heat work 101 when I ask this. I am referring to the fact that heat work continues through a hold.

If you want to say that you are comparing two ways of firing the same glaze, I get that.


Christ,
Yes that is exactly right, "the two firings are worlds apart." On the forums, and is some literature It is an accepted theory that the only way you can get iron red instead of brown is to use slow cooling. One firing is controlled with ramps and soaks and the other is not. Both firings did produced iron reds. The cones are included in the photos to show neither kiln was over, or under fired at cone 6. My hope is that the test can be repeated by those with older kilns. That's all I wanted to show. The discussion got off on SCM concerns that many are interested in. In an effort to keep it simple I'm sorry I did not explain it well enough. Your understanding of heat-work is probably OK.
John255


John255

#23 Chris Campbell

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Posted 27 June 2013 - 09:33 PM

Thanks for the explanation.
I appreciate it since I have never fired iron red glazes ... amazing actually that I have spared myself any frustrating clay experience.Posted Image

Chris Campbell
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#24 John255

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Posted 28 June 2013 - 08:34 AM

Thanks for the explanation.
I appreciate it since I have never fired iron red glazes ... amazing actually that I have spared myself any frustrating clay experience.Posted Image


OK Chris, sounds like you are on track now.
I just looked at your work and find it absolutely gorgeous.
I have no idea how you do that.
It's far beyond anything I could do.
Regards,
John255
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#25 Chris Campbell

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Posted 28 June 2013 - 10:42 AM

Thanks John ... finding the proper niche for firing that work successfully is what has me so interested in heatwork, ramping, cooling etc. Controlled cooling has cut my loses by at least half but I think controlling the actual heatwork will go even further with this.

At the last NCECA there was an excellent presentation on the future of firing and heatwork. Ever since we potters got computers on our kilns and started playing with them, the importance of knowing the real heatwork is going up. Most of what they were saying went over my head, but once they started showing pictures I began to get it and it was exciting and fascinating.Posted Image This is just early days though and there is a lot more research to be done.

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#26 Pres

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Posted 28 June 2013 - 10:56 AM

I guess I am one of the really oldies here. I fire without a kiln setter or a computer controlled system of any kind. It was a strange order for L&L back in the day, and they did not want to sell one that way, but after explaining what I wanted they made the kiln. The reason for this is that I wanted to be able to fire down or hold at a temperature for a little longer. In the end, It is a pain to babysit, but I can do any of the ramping up or down I need. Only problem is being certain of temp. I have gotten pretty good at checking this by kiln color. These days, if I buy a new kiln, it will have the whole nine yards!Posted Image

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#27 Bob Coyle

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Posted 28 June 2013 - 11:24 AM

I'm not so sure how you would calculate heat work. Even with a computer controlled kiln there is a lot of slop. I measured the voltage difference on three K thermocouples I have and they varied by as much as 75 F at around 2100 F. small changes in placement of the thermocouple and kiln loading also make a big difference. I always watch the cones.

I don't think one persons ramp can be reproduced very closely from one kiln to another. From what I found, reproducibility is the important thing. Once you have a good ramp that works with your glazes... stick with it and don't mess with anything. Even then your thermocouple will drift as it ages and your ramp will change over time.

#28 John255

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Posted 28 June 2013 - 12:45 PM

I guess I am one of the really oldies here. I fire without a kiln setter or a computer controlled system of any kind. It was a strange order for L&L back in the day, and they did not want to sell one that way, but after explaining what I wanted they made the kiln. The reason for this is that I wanted to be able to fire down or hold at a temperature for a little longer. In the end, It is a pain to babysit, but I can do any of the ramping up or down I need. Only problem is being certain of temp. I have gotten pretty good at checking this by kiln color. These days, if I buy a new kiln, it will have the whole nine yards!Posted Image


Pres,
I too know all about kiln baby-sitting. I've probably spent more time on my knees watching cones than the new Pope spent praying.
I was just about to get serious with this guy who is selling a computer control kit for kilns for about $250 when a computer test kiln came available here for $300.
You may be interested:
http://www.ebay.com/...=item19da88ef5e
Regards,
John255
John255

#29 John255

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Posted 28 June 2013 - 01:01 PM

I'm not so sure how you would calculate heat work. Even with a computer controlled kiln there is a lot of slop. I measured the voltage difference on three K thermocouples I have and they varied by as much as 75 F at around 2100 F. small changes in placement of the thermocouple and kiln loading also make a big difference. I always watch the cones.

I don't think one persons ramp can be reproduced very closely from one kiln to another. From what I found, reproducibility is the important thing. Once you have a good ramp that works with your glazes... stick with it and don't mess with anything. Even then your thermocouple will drift as it ages and your ramp will change over time.


Bob,
Very fine post.
Glad to have your data on thermocouples.
I've been concerned about that, and don't trust them.
I still watch for the beginning of the cone bend at 100/hr.F to start the soak while observing the tip just touching to start the first down ramp.
Completely agree we should not rave about our ramps.
Regards,
John255
John255

#30 Pres

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Posted 28 June 2013 - 05:01 PM


I guess I am one of the really oldies here. I fire without a kiln setter or a computer controlled system of any kind. It was a strange order for L&L back in the day, and they did not want to sell one that way, but after explaining what I wanted they made the kiln. The reason for this is that I wanted to be able to fire down or hold at a temperature for a little longer. In the end, It is a pain to babysit, but I can do any of the ramping up or down I need. Only problem is being certain of temp. I have gotten pretty good at checking this by kiln color. These days, if I buy a new kiln, it will have the whole nine yards!Posted Image


Pres,
I too know all about kiln baby-sitting. I've probably spent more time on my knees watching cones than the new Pope spent praying.
I was just about to get serious with this guy who is selling a computer control kit for kilns for about $250 when a computer test kiln came available here for $300.
You may be interested:
http://www.ebay.com/...=item19da88ef5e
Regards,
John255


Link to the plug and play controller was for 15 amp. My Land L is 78 amp. Don't see compatibility there. Thanks for the link, and if I find one I can wire into the line and then put thermocouple in the kiln, I might. . . . think hard about it. Heck my L&L is only 30 years old.

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


#31 Bob Coyle

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Posted 28 June 2013 - 06:56 PM


I'm not so sure how you would calculate heat work. Even with a computer controlled kiln there is a lot of slop. I measured the voltage difference on three K thermocouples I have and they varied by as much as 75 F at around 2100 F. small changes in placement of the thermocouple and kiln loading also make a big difference. I always watch the cones.

I don't think one persons ramp can be reproduced very closely from one kiln to another. From what I found, reproducibility is the important thing. Once you have a good ramp that works with your glazes... stick with it and don't mess with anything. Even then your thermocouple will drift as it ages and your ramp will change over time.


Bob,
Very fine post.
Glad to have your data on thermocouples.
I've been concerned about that, and don't trust them.
I still watch for the beginning of the cone bend at 100/hr.F to start the soak while observing the tip just touching to start the first down ramp.
Completely agree we should not rave about our ramps.
Regards,
John255


Yes, I don't pay much attention to the actual top temperature recorded. Two sets of witness cones, one high, one low tells the tale. I watch the ramp till it is close, and then watch the cones.

I have a small test kiln with a kiln sitter and find running the same ramp resulted in top temperatures that differ by 50- 75 F when the sitter shuts off... And that is with the thermocouple measured to be the same distance from the wall . If I push it in an inch further, the setter drops almost 100 F lower than it reads an inch closer.




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