pots exploding in Cress XL23 Firemate kiln

[ravengirl1220]

OK...this is a little embarrassing...but I'm trying to determine if my kiln is not firing correctly or if the pots weren't really bone bone dry before I bisqued.

 

I have a Cress XL23 - the automatic "firemate" never worked (this was a free kiln!) and the last time I fired it the Turbo fire button was stuck. The last time I fired it was a year ago, and as I recall, pots blew up, and I figured that was because it was firing way too fast for a bisque.

 

This time, I managed to get the Turbo fire button unstuck, but not before a few pots blew up (I had forgotten about the Turbo fire button - had never had this on previous kilns.)

 

I had the Firemate turned to manual and the firing wheel between the start symbol and 0 (about as low power as one can go), and still pots are blowing up. Evenly thick pots are blowing up - pots that appeared to be bone dry. I had the kiln cracked several inches and peeps clear. It has rained quite a bit in the last couple of days, so I thought maybe humidity was a factor. I tried to just put the kiln on low low heat (between the start symbol and 0) and have the lid completely cracked but still things blew up after about 15 minutes.

 

The Cress I had before - turned on and off (made a clicking noise) to heat up slowly. I'm not sure if this was a function with the wheel or if it should do that even when on manual.

 

This kiln is _not_ doing that - it's just "on". I can't tell if it's firing too fast, or if it's a problem with my pots being damp.

 

Does anyone have any ideas/experience with this?

 

Many thanks,

 

Julie

[Pres]

OK...this is a little embarrassing...but I'm trying to determine if my kiln is not firing correctly or if the pots weren't really bone bone dry before I bisqued.

 

I have a Cress XL23 - the automatic "firemate" never worked (this was a free kiln!) and the last time I fired it the Turbo fire button was stuck. The last time I fired it was a year ago, and as I recall, pots blew up, and I figured that was because it was firing way too fast for a bisque.

 

This time, I managed to get the Turbo fire button unstuck, but not before a few pots blew up (I had forgotten about the Turbo fire button - had never had this on previous kilns.)

 

I had the Firemate turned to manual and the firing wheel between the start symbol and 0 (about as low power as one can go), and still pots are blowing up. Evenly thick pots are blowing up - pots that appeared to be bone dry. I had the kiln cracked several inches and peeps clear. It has rained quite a bit in the last couple of days, so I thought maybe humidity was a factor. I tried to just put the kiln on low low heat (between the start symbol and 0) and have the lid completely cracked but still things blew up after about 15 minutes.

 

The Cress I had before - turned on and off (made a clicking noise) to heat up slowly. I'm not sure if this was a function with the wheel or if it should do that even when on manual.

 

This kiln is _not_ doing that - it's just "on". I can't tell if it's firing too fast, or if it's a problem with my pots being damp.

 

Does anyone have any ideas/experience with this?

 

 

Many thanks,

 

Julie

 

What sort of test do you do to check for bone dry-cheek test all pots? This time of year, I fire very slow in the water smoke as there is too much moisture in the air with the cold coming in. I can't really help you with the turbofire, as I have never used one.

[Benhim]

I've never fired a Cress either. With my bisque pots I fire slowly. I have the bottom element on low for about 12 hours, usually overnight. Then I turn the other element on and wait 4 hours, then medium for 3 to 4 hours, then high until done. I keep my lid propped about an inch and the ports wide open all night and until I turn the second element on. Once the second element goes on I drop the lid and plug holes. I also have an envirovent which I have one to help circulate the air and remove water vapor from the chamber. My kiln has infinite dials so I often edge up slow if I have large pieces in the kiln instead of low, medium, high.

 

Your problem sounds like chemically bonded water boiled inside your ware and caused it to break because your kiln temperature rose too fast. Beginning on a low temperature with only one element in the bottom of the kiln on helps burn off the chemically bonded water slowly below boiling temp. At this low temp (under 212) it takes a long time to burn it all off. If the pots are not bone dry it takes a little longer. My college had an 18 hour low hold time on their bisque because students don't pay enough attention and will load wet pots. They had few explosions which were usually beginners pots that were thick and still slightly wet.

[ravengirl1220]

I've never fired a Cress either. With my bisque pots I fire slowly. I have the bottom element on low for about 12 hours, usually overnight. Then I turn the other element on and wait 4 hours, then medium for 3 to 4 hours, then high until done. I keep my lid propped about an inch and the ports wide open all night and until I turn the second element on. Once the second element goes on I drop the lid and plug holes. I also have an envirovent which I have one to help circulate the air and remove water vapor from the chamber. My kiln has infinite dials so I often edge up slow if I have large pieces in the kiln instead of low, medium, high.

 

Your problem sounds like chemically bonded water boiled inside your ware and caused it to break because your kiln temperature rose too fast. Beginning on a low temperature with only one element in the bottom of the kiln on helps burn off the chemically bonded water slowly below boiling temp. At this low temp (under 212) it takes a long time to burn it all off. If the pots are not bone dry it takes a little longer. My college had an 18 hour low hold time on their bisque because students don't pay enough attention and will load wet pots. They had few explosions which were usually beginners pots that were thick and still slightly wet.

 

 

Unfortunately I can't control elements in various parts of the kiln - it's all or nothing. But with my old Cress, the "wheel" - (does the autofire) - could be set to manual and #2 = low, 5 = med, etc. I had wheel on this one set between beginning and 0. I'm starting to think that this kiln has one setting - high. I tried again today - and I had the kiln cracked for an hour at just past the beginning on the wheel, then closed the kiln for an hour, then bumped it up to 1. I was going to let it sit for 2-3 hours. I went out and came back - and in that time the darn thing fired and the cone sitter dropped. With the preheat that would be about 4 hours for a bisque - which is probably normal considering this is a much smaller kiln than I had before (it's about 3.5 cu ft and last one was 7.5). But still - the old kiln I went up to at least 5 or 6 on the dial for a bisque - and this thing was completely done on level 1.

 

We have a local ceramic supply store that has a technical guy that can take a look at it and I'll give that a try.

 

I agree that I probably fired it way to fast yesterday - that "turbo fire" button should not have been on and I had set it to "2" on the wheel - but only because that used to mean "low" on my old kiln.

[JLowes]

I found on my Knight kiln that even with one set of elements on "Low" I was getting too much heat rise for an overnight candling. I know this now because I bought a pyrometer and with its guidance I leave the lid open and place two kiln shelves (I have a larger kiln also) with one shelf covering half the open top and the second shelf varying the opening to control the heat. I found about 25% opening to be about right for my kiln, loaded medium to heavy.

 

I don't know if something like that could be adapted for your kiln to control the low end temperatures. It may just be that your kiln needs maintenance and parts. Maybe your tech friend will diagnose an issue that is correctable. Good luck.

 

John

 

P.S. "Turbo" .... must be a 1980s era kiln, lol.

[ravengirl1220]

Unfortunately I don't have a larger set of kiln shelves - this sounds like a good idea. I got in touch with Cress today and they think there is a malfunction of the switch in the wheel. They think it is indeed blasting on high and there's no way to ramp it up properly. Our local tech guy is coming to look at it. Apparently it could also be an element malfunction - sometimes this causes a kiln to fire very slowly - other times it fires too hot and too quickly.

I found on my Knight kiln that even with one set of elements on "Low" I was getting too much heat rise for an overnight candling. I know this now because I bought a pyrometer and with its guidance I leave the lid open and place two kiln shelves (I have a larger kiln also) with one shelf covering half the open top and the second shelf varying the opening to control the heat. I found about 25% opening to be about right for my kiln, loaded medium to heavy.

 

I don't know if something like that could be adapted for your kiln to control the low end temperatures. It may just be that your kiln needs maintenance and parts. Maybe your tech friend will diagnose an issue that is correctable. Good luck.

 

John

 

P.S. "Turbo" .... must be a 1980s era kiln, lol.

 

[Marko]

I once was asked by a potter friend, when I was just learning how to load a kiln and fire, to place a large plater in the kiln for him because he was out of town but needed this plate fired ASAP. So I did as he asked. Ok, maybe he could have told me that putting a greenware plate in a kiln that has been drying in a ice cold shop might take a while to heat slowly, but I guess he thought I would have known better . His bad or my bad, I don't know, but it was very bad for the plate. KABOOM!!!

 

Lesson learned: always consider temperature, humidity, thickness and being hasty. I haven't ever had this problem again, but I still think about it everytime I load my kiln. Anyway, I always feel the clay for dampness or coolness. If it's cool to the touch in a warm room I give it more time. But even after this I always start firing slow and easy, for bisque. Over time you will get to know how your clay reacts to time and your weather conditions. Anyway, live, learn and have fun.

[Idaho Potter]

I have a older (1985)Cress kiln with Kiln Sitter. I think your switches are faulty. My kiln is like yours, no separate firing areas, and I use it just for bisque. Rather than losing another kiln load of pots, it seems a better idea to have a tech take the kiln sitter apart and fix it. If at a later date you are concerned with your work being dry enough for firing, try using your stove's oven to force dry your pots. A couple of hours at 250 to 300 degrees relieves your mind even if the pots pass the "cheek test". This temp isn't enough to release chemicals into the house, just finish drying the pots. For heaven's sake, don't put leather hard work in your oven, just the pots that are a little questionable about dryness.

[Benhim]

Yes your switches appear to have failed. You'll have to repair or probably replace the switch that controls your temperature. My technical knowledge ends about there, you'll want to consult a technician, and or a diagram which shows the wiring and components of your kiln. It's probably a very simple part replacement, the sitter kilns aren't terribly complicated.