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frankbonatelli

Expert knoledge and eyes needed for a failed cone 6 fireing

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Right all you skilled artisan's 
Firstly thanks in advance for your shared knowledge and ideas. 
Right to it then shale we
So I have a new to me kiln make model unknown age unknown. It was free to me so i spent a few coins to refurbish it to usable status. This is a reduction kiln 220 volt 3 elements three manual controllers rated to cone 6. very simple to use. Any ways it is my second use of the kiln, first was to cone 4 and it took a similar amount of time to achieve this as my cress does. +/- 4 hours till the sitter trips once i reach 100% energy usage on the manual dials. The Cress has served me well for 20 years with and I'm extremely familiar with all its little quirks. Cone 4 takes four hours cone 6 takes Six. This new one is similar in cone 4 firing but the just fired cone six is an epic fail.

So that's the back story.
The new kiln was run in the same manner as the cress and at 100% energy usage on all three dials I start my timer. After ten hours there still was no sign of it shutting down so I manually tripped the sitter. Let it cool over the next day and looked in toady. What I found is a confusion to me. 
below are a few shots of what i found and maybe with the skill of a billion eyes and minds some one can shed light on it.

First question I have is - do cones have an expiry date? Sounds dumb but if i don't ask......... See in the foto it did not even droop a little. not one bit. That seems odd to me.
Second do we see glazes under fired or over fired? If question one is a yes then maybe it was to old a cone and i may as well have used a nail for a cone. Or is it under fired and after ten hours at 100% they still had not achieved temperatures needed for cone 6 firing.

Ive also noted that the shinier bowl is lower down in the kiln to the other four so maybe this is indicating element temperature variants between the three coils. Hmmmmm
One last thing of note, I'm from the north and the temperature outside the Kilns was a balmy -25 C (-11.2 f for my southern brothers and sisters). This has never bothered my Cress before but may be this too is a factor on timing.

So that's my story today, Thanks again for your ideas

Cone unbent and four bowls

coneSIX-01.jpg

coneSIX-02.jpg

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(post moved from Clay and Glaze Chemistry)

No, pyrometric cones do not expire. 

An electric kiln rated as having cone 6 as a maximum firing temperature with worn elements is going to struggle to reach cone 6 even in the best of circumstances.

The blue bowl looks like the glaze is on too thinly in parts of it, the two in the foreground definitely look under-fired. One could look glossier if the fluxes used in it melt at a lower temperature than the others but that doesn't mean it reached maturity, or that part of the kiln could have gotten a bit hotter. Trust the cones, put them on all the shelves.

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I think you need to check your coils with a multimeter.  Check your Cress manual for voltages, and then test. Neil can tell  you more, but from what I see in your images looks like one of the top coils is kaput. This should be a pretty easy fix if you are handy, even if not, an electrician could do the job quickly once you have the coils.

 

best,

Pres

 

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If your kiln is rated to cone 6, that means it can only get to cone 6 if the coils are in perfect condition. As soon as the resistance of the coils changes due to wear, it will no longer be able to get to cone 6. The best way to test them is to check the resistance of the elements with the ohm setting on a multi-meter. You can get a functional digital meter for under $20. First you'll need to find out what the resistance should be- you can get that info from the manufacturer or the wiring diagram. Then test the elements by opening the control panel (unplug the kiln first) and putting the meter probes on the ends of the elements. In a typical kiln, elements should be replaced when they are 10% off from original. In your situation I wouldn't expect them to be able to go that far before cone 6 is a problem.

You also need to rule out that there are any other problems, like a bad switch, etc. To do that, put the kiln on high and let it run for 10-15 minutes. Then carefully crack the lid and see if all the elements are glowing. If everything's glowing, then you probably just have worn elements. If any elements aren't glowing, then you need to figure out if the element is bad, or if there's a bad switch or connection somewhere in the system.

Pres likes this

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Fantastic information all
Thanks for sharing. I have peeked at the elements and know for certain all switches are good, all three elements glow equally so power is getting to the elements. As for make model for wiring there is none. No name and no model. I'm suspecting the elements as well but did truly wonder if cones expire (Thanks for the straight answer on that with out judgment)
Test procedure will help and ill post any further results as soon as it warms up enough to spend some quality time with it. Till then the old Cress will continue to preform its duties

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I was about to ask the same thing. I fired a kiln last night with a mini bar 06 white cone. It must be 25-30 years old. Worked fir. It was -6 F.

The shiny glaze looks like a different glaze than the white ones. It could have started to flux before the other glaze did just from the composition.  Check your element as Neil suggests.

Marcia

 

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I use electronic controllers on our kilns, so if I had to get cone 6 in a cone 6 kiln I would go for 4 or 5 (which ever is achievable with current elements) and then do the last cone + with heat work.

Can you do that with a sitter by loading a cone pack you can watch with 4/5/6 and level off at 4 full bend and 5 bending then hold temp until 6 bends? 

Edited by Stephen

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2 hours ago, Stephen said:

I use electronic controllers on our kilns, so if I had to get cone 6 in a cone 6 kiln I would go for 4 or 5 (which ever is achievable with current elements) and then do the last cone + with heat work.

Can you do that with a sitter by loading a cone pack you can watch with 4/5/6 and level off at 4 full bend and 5 bending then hold temp until 6 bends? 

It's really difficult to hold temp on a manual kiln. You have to have a digital pyrometer and sit there turning the switches on and off.

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On 2/13/2018 at 10:42 AM, neilestrick said:

@frankbonatelli Post some pics of the kiln. We may recognize the manufacturer.

As soon as I get back home ill do just that. Its an octagon styled kiln with three element controls and a manual Kiln sitter. I've had it for a year now and only fired it twice now. I tend to trust the ole Cress with all my wife's better pieces. 

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