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Chilly

Recalibrate Or Just Set To Lower Temperature?

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Chilly    329

What would you do?

 

The (community centre) kiln now has new, evenly coiled, non-droopy elements, and it overfired.  Cone 7 was well down with the programmer set to 1241C, with final ramp rate of 150C.  - I checked the cone packaging before setting the programmer and wanted ^6.

 

So, should we get the kiln techs back to re-calibrate/adjust the programmer?  The ones who said there was nothing wrong with the droopy/stretched straight elements .  It's a MITSCO 3000 I think, or should we just drop the final temperature. 

 

It also overfired on ^06, but as we didn't have any cones we don't know by how much but I can tell by some of the glazes.  We now have cones, so will be checking the result next glaze firing.  The kiln fires unattended overnight so the tutor has never bothered with cones, but I always use them for ^6.

 

 

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Bob Coyle    113

If your glazes were calibrated to mature at cone 6 down, then I would re-calibrate. I trust cone heat work more than what the controller temperature says.

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Babs    386

Unless I got totally screwed when coming to the southern hemisphere 1241C, depending on the rate of firing is well above C6 C6 in my op. is 1201-1222d  C7 1215-1240dC First no. being a rise of 60d /hr, second no. 150d/hr

Is this on the right lines??

Orton standard pyrometric cones that is.

SO  naybe check this before adjusting antthing.

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Chilly    329

Babs - just re-checked the packet of cones, and quite clearly says Cone 6 1241C.  (^7 pack says 1255C and ^8 = 1269C.)

 

But you got me thinking, so I checked the 8 pottery books that i have at home, and found the following:

 

Pitman - Kilns & Kiln Firing - 1969  = 1200C

A&C Black - The Potter's Dictionary - 1975 = 1222C @ 150C hour

Teach Youself - Pottery - 2001/2003     =   1200C

Lark Ceramics - Alternative Kilns.. - 2004   =    1241C @150C hour

A&C Black - Ceramic Faults.. - 2005      =      1241C @150C hour  -  with a footnote:  "Following recalibration in 1996 these cones now bend 10-20C later than previously"  - which applies to ^5, ^6, ^7 and ^8

 

The other books didn't have charts at all, so perhaps they couldn't decide what info to publish.

 

I then checked the Orton website and found the same temperatures as printed on the packs of cones. 1241C for ^6.

 

 

Confused?  I am.

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Babs    386

That's 2 of us, so when all the info posted re newish trend about firing to C6 and it looks just like high fired, well........... Looks like new C6 is equivalent to  old C 7/8 what a surprise that the glazes look just like high fired cos that is what they are!!

What are your glazes looking at at the new C 6??

God I wished I hadn't read your post!!! :huh:  <_<  :(

Fortunately the glazes I use are ones or versions of ones from the good old days which I mix myself and fire using a kilnsitter,  watching temp, colour, time and cones, cones!! there goes my logic, :o

Do any of the forums gurus have answers?

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Bob Coyle    113

 

Do any of the forums gurus have answers?

Hey Babs. Remember, this is ceramics. Cone values, ramp times, glaze formulations, clay bodies all have so much variation from one persons setup to the next that the only way to get good results is to test everything first and once you have a working clay body...formula...ramp, then try like hell to reproduce it every time you make a run. Even then kiln loading and position ( not to mention the kiln gods) will cause variations both good and bad.

 

That's why opening the kiln after a run always feels like Christmas morning!

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bciskepottery    925

Cones bend from heat work, not by reaching a certain temperature. It took me a while to understand that the rate of temperature increase had an impact on the temperature reading (seems the faster the rate of climb for the last two or so hours, the higher the temperature needed; while a slower rate of climb over the last two or so hours would end with a lower temperature). Then, the type of cone (self-standing, large, small) also has different temperatures associated with maturity.

 

A simple check would be to fire the next load to cone 5 on the programmer, with cones inside to see what the heat work actually was -- might be more towards cone 6. Over time, as the elements wear, you'll end up having to program back to cone 6 to reach cone 6 on the temperature scale. If the programmer has a cone offset, you might want to see if it needs adjustment or if there is already an offset that needs to be adjusted to accommodate for new elements.

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Chilly    329

Just found another oddity/anomoly....

 

In Teach Youself - Pottery - 2001/2003 the cones chart just gives Cone no, temp n F and C, colour in kiln and bisqeu/stoneware/porcelain etc.  Buried in the text beside it says "I have compiled the chart" - what you mean it's not come from the cone manufacture?  "The cone numbers used are for Staffordhsire cones" - what I've got Orton cones!

 

So, reading up more on this different manufactures make their cones bend at different temperatures.  So a jar of commercial glaze that says ^06 is wasting it's breath.

 

Goes and hides in a darkened room.

 

The only thing I can really say, is that the last ^6 firing was overfired, nevermind what the cones/controller says, I can see by looking at the glazes that they are not what I expected, they were tooo runny,  so next time I'm going to drop the temperature by xx degrees.  Where xx = whatever I'm feeling like on the day, coz that's what ceramics feels like.

 

So, kiln gods, do your worst, I'm ready........ :angry:

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Babs    386

 

 

Do any of the forums gurus have answers?

Hey Babs. Remember, this is ceramics. Cone values, ramp times, glaze formulations, clay bodies all have so much variation from one persons setup to the next that the only way to get good results is to test everything first and once you have a working clay body...formula...ramp, then try like hell to reproduce it every time you make a run. Even then kiln loading and position ( not to mention the kiln gods) will cause variations both good and bad.

 

That's why opening the kiln after a run always feels like Christmas morning!

 

I WAS happy most of the time with what was happening on my christmas mornings! Because I glancd at this post it got me wondering....

I did buy a new pyrometer , but often trip the sitter because I feel that kiln is hot enough thank you and the cone is just fluffing with me.

I have a direct line with my kiln god, he can be relegated to the ranks of imps any time.

Never thought of kiln opening as Xmas am. I'll have to let that mull a while.

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Babs    386

You be cool Babs...  

More like

wouldn't you say Chilly??

Yeh Bob Know your glazes, kiln,log of firing, and go from there.

By the research chilly has done, I've been oblivious of the recalibration of the cones since 1996   , so

just refer to the log book, wine bottle and whatever else works for you on the day, just get on with it.

Thanks for the tune, I'm meant to be doing business books , accountant tomoz... Aus financial year in June.

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Tom    4

I work with 4 kiln controllers at 3 different locations all the same brand.  none of them fire the same but all fire too hot compered to sight cones.  As I chart kiln firing electric and gas for these kilns I know about to set the controllers to get the firing I want.  every month or so to see if , now, I use sight cone at the sight holes to check  to see if the kiln is still on track.  use the controller read out as a guide their never right,  get to know your kiln and all its warts.

 

Tom 

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Chilly    329

And just to be contrary (because I'm a woman, yeah, yeah) I carefully looked at all the pots this morning in good daylight, and actually, I'm rather pleased with them all.  Yes, even the ones that ran and stuck to their cookies and broke !

 

Think I'll stick with that setting for the next firing, I just have to remember to re-read the other post about "footrings" and ways to arrest the glaze drips.

 

Thanks you kiln gods, you've opened my eyes.  Thinks out loud:  how, how can I make my own kiln get that hot, it stalls at around 1180C despite being rated to 1300C.  Two hour soak?

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Chilly    329

 

You be cool Babs...  

More like

wouldn't you say Chilly??

 

Can't find one with "white, white wine" lyrics, but I like the thought.

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