Looooong Cool Down

[Chantay]

On Wednesday I was able to warm the garage a little, up to 37, loaded the kiln with work to refire. Cone 6.  I programmed in a slow cool with an hour hold at 1800. I have a Skutt 1018 with controller.  Things started to look sketchy when after entering the program I hit the review button.  The numbers flash by on the display VERY quickly.  I rechecked the program about 5 times.  Apparently I missed something.  Through the evening I watched the firing, then I fell asleep, mistake.  When I woke up and checked the kiln it was holding at 1640 F.  I have no idea how long it had been at this temp.  I'm guessing around 8 hours.  One problem I have with this kiln is no matter how I place the witness cones I can't see them during the firing.  Being new the peep holes are very small, haven't been worn down any.  So I shut the kiln down and waited.  I cracked the garage door to help cool down.  The garage was very toasty at this time.  Once the kiln had reached 540 I quickly cracked the kiln lid to peak in.  I was expecting everything to be melted down.  Surprise.  No melt down of pieces. Last night I unloaded the kiln and took stock of my long hold experiment. 

 

The first pic is of a bowl from a previous firing.  I posted about it here:  http://community.ceramicartsdaily.org/topic/5491-new-pinholes-old-glaze/

 

The Third pic is same bowl after refiring and long hold.  Color is a brown with hints of purple.  I had mixed glaze with a few drops of elmers glue and applied over the blisters.  barely visible, you can see some of the blisters now just look like unglazed spots.  I was using recycled clay, standard 240. I wonder if there was some foreign material in the clay that caused this.  On the other items in the kiln being refired it was hit or miss.  Items with vertical surfaces fared better that those with flat or or angled surfaces.

 

Second pic is cone pac from firing.  Cones 4, 6, and 5.

Another item in the kiln was some heart pendents.  These look pretty good. They are a red glaze.  A few were stuck to the bottom of the bead holder I had constructed as the nicad wire had sagged. Conclusion at this time, an 8 hr. soak isn't going to melt everything to the kiln shelf, but some colors look over cooked.

 

 

 

 

[Chris Campbell]

Well, your cone pack doesn't look right ... Are you sure you put in 4,6 &5?

Two look way over fired and the third hasn't moved much.

 

Have you by any chance purchased Mastering Cone 6 glazes? This would be a great resource book for you. Re-firings are always iffy situations so make notes on what happened with these loads so you will be able to adjust the next firings.

 

Also your holes are not going to get bigger. As you load your kiln you should check your placement to make sure you will be able to see them. They are HARD to see when the kiln is hot so it really helps to know where they are exactly. Some people see them easily and others do not. I have a hard time seeing them but my neighbor can just take a quick glance and sees them perfectly well.

[Diane Puckett]

I have had refires add blisters but never make them go away.

[Mark C.]

I'm not a big electric guy but will add that 1st glaze looks like a rutile base which is notorious for pitting . The cones as Chris said look like the middle one is not what you thought it was.

As for seeing them space them tighter in pack so they are not as long and put them at an angle to spy opening and put something behind them as a visual backstop. You can use a laser light to see better I'm told .Get  the right eye protection Thats is what I favor as I can see them well but it takes some time. There has been many posts on this subject and looking thru them would be helpful for you.

Mark

[Chilly]

Chantay this might help http://community.ceramicartsdaily.org/topic/5421-cannot-see-witness-cones/

[bciskepottery]

My guess is you never reached cone 6; on your cone pack 4 and 5 are down, but 6 has barely moved. I would guess when you programmed in the cool down, the kiln over-rode the top temperature and, instead, rose to 1800, held for an hour, then started cool down. The long 8 hour soak at 1640 probably generated enough heat to bring down 4 and 5 cones. On your cone packs, place the cones in order -- 4 - 5- 6; makes it easier to read and a more logical sequence.

 

As for the glaze, you might have gotten more Elmer's glue in the touch up than actual glaze. The Elmer's burned out and there was nothing/not enough left to repair the blister. Plus, if you did not reach cone 6, that might have prevented the glaze around the blister from fully remelting.

[Mark C.]

I'm a little thick on getting the cones out of order as I just have never seen that-thanks bciskepottery I see that now

Mark

[Babs]

Chantay, only because it wasn't obvious to me.........Are you placing your cone set at right angles to the peephole so that the lowest cone flattens then tne next one becomes visible and so on? To start with I placed the cone set parallell and struggled to see around corners!!  At right angles it makes sense to place as bcisket says, you see them melt one by one as the temp rises.

Sorry if this is glaringly clear to you, and not part of your question.

Babs

EDIT   At right angles to the wall in which the peephole is placed!

[Chantay]

Thanks for the suggestions everyone. I hadn't thought of putting them in at a right angle. I'm sure that will help. Mastering cone 6 glazes, check. Eye protection, check.  Put cones in correct order, check. 

 

I saw the display read 2450 I believe. Don't have notes in front of me. Next firing I won't do a long hold and see what the cones do. Could be the reading is off? I'm confused about the cones as the glazes look well done. Not like they normally look. Hoping to fire again Sunday. Will start early and watch through the end.

[bciskepottery]

2450F would have put you in Cone 12/13 range . . . and likely melted all your cone 6 clay and glazes.

[neilestrick]

Bruce, glad you're back. The kiln probably fired to what it thought was cone 6 (needs calibration), then something went bad during or after the controlled cooling. If it had only reached 1800, 8 hours soak would probably not have been sufficient to put cone 5 down. I once fired an Anagama that we held at 1850 for 5 days before cone 5 went down.

 

As to why it was holding at 1640, I have three thoughts. One, you screwed up the programming. It happens. Any chance you put in 10 hours instead of one hour? Two, you have a sticky relay. Did you have to turn the power off to get the kiln to stop heating, or just push 'Stop'? In a kiln that size, if one relay is sticking 'on', that means 1/2 the elements are on, and the kiln won't cool down. Third, your controller has gone bad. Hit the review button again and write down what it says the last program was. Post it so we can see.

 

If the display read 2450, you've got a problem somewhere. That controller isn't programmed to work at that temperature. Did you get any error code during all this? If the thermocouple in good condition?

 

I agree that the pinholed glaze looks like one that would be prone to pinholing. We use a lot of 240 in my studio and have never had it cause pinhole problems.

[Chantay]

After reading your post Neil I went back and rechecked the controller and my notes.  I believe I entered the correct info into the controller.  When I found it still on I turned it off by pushing stop.  Ramp/hold settings:

 

RA 1   150

^F1     200

Hld 1   1.0

RA 2    400

^F 2     1949

Hld 2     0.00

Ra 3      120

^F 3      2170

Hld 3     0.20

RA 4     300

^4         1900

Hld 4     0.00

RA 5     35

^F 5      1800

Hld 5     1.0

RA 6      31

^F 6      1600

Hld 6     0.00

 

I'm waiting to fire again till I can stay home through the whole firing.  Probably Thurs. day.  This is a newer kiln, maybe 10 firings.

 

Thanks for all the help.

 

 

 

 

 

 

[neilestrick]

The other possibility is that the kiln had reached a point where it was just naturally cooling very slowly. At 1640 it's possible that it couldn't cool as fast as you had programmed it, and the controller wasn't actually holding the temperature. It was just cooling as fast as it could, especially if there was a lot of work in the kiln holding in the heat. With my big kiln, below 1800 the elements don't ever come on in a controlled cooling besides just keeping the sections even.

[bciskepottery]

Bruce, glad you're back. /quote]

 

Tried for parole but was turned down (actually, my petition was not answered). So, as long as I'm stuck here, might as well play.

 

On a more serious and relevant side, if the peak temperature programmed was 2170F, then I'm not surprised the 6 cone did not drop; even with a 20 minute hold it likely did not generate enough heat work to reach cone 6. I'm not sure if there is a need for a one hour hold at 200F for a glaze load.

[Benzine]

I'm not sure if there is a need for a one hour hold at 200F for a glaze load.

I wouldn't think so. When I run the "Fast Glaze" setting on my class kiln, it's well over 200, in no time, with no glaze issues, even on the freshly glazed wares.

 

On another side note, where did you go?

[neilestrick]

After reading your post Neil I went back and rechecked the controller and my notes.  I believe I entered the correct info into the controller.  When I found it still on I turned it off by pushing stop.  Ramp/hold settings:

 

RA 1   150

^F1     200

Hld 1   1.0

RA 2    400

^F 2     1949

Hld 2     0.00

Ra 3      120

^F 3      2170

Hld 3     0.20

RA 4     300

^4         1900

Hld 4     0.00

RA 5     35

^F 5      1800

Hld 5     1.0

RA 6      31

^F 6      1600

Hld 6     0.00

 

I'm waiting to fire again till I can stay home through the whole firing.  Probably Thurs. day.  This is a newer kiln, maybe 10 firings.

 

Thanks for all the help.

 

Finally had a chance to look closely at your schedule. I think I found the problem: Rate 5 was 35F/hr from 1900F to 1800F, so there's 3 hours right there plus an hour hold. Rate 6 was 31F/hr to 1600, so there's another 7 hours there. I think it was following your schedule just fine. Any reason you're trying to cool so slowly?

[Nancy S.]

Not on the kiln topic, but why did you opt to mix Elmer's glue with your glaze? Why not just put the glaze on directly?

 

When I've re-glazed due to defects and re-fired, I just slather on another layer or two of glaze over most of the area, not just on the spots that had issues.

 

As for the blistering, a slower fire (not necessarily a slower cooling) may help. You may want to also invest in Harry Fraser's book Ceramic Faults and their Remedies. (Fairly inexpensive on Amazon.)

[Chantay]

Nancy,  I was using the glue to get the glaze to adhere to the pot better.  A thin coat held, without the glue a thick coat did not.  W hat I cant understand is why there are blisters now and on only some of the pieces.

 

Niel,  Thanks for looking at the program.  I guess I was tired when I calculated the firing time.  I was off by about 2 hours.  I plan to fire some test pieces tomorrow with the same glaze.  My plan is to us the cone setting with a med ramp.  The reason I was doing a slow cool was because most of the pieces in the kiln were being refired due to blistering.  All the blistering did disappear but many of the pieces now have pinholing and the color is unattractive. 

 

I don't like not knowing why the refired pieces have the pin holing.  I am worried this will be a repeat problem as I like this glaze.

 

Thanks again for your help. 

[neilestrick]

Nancy,  I was using the glue to get the glaze to adhere to the pot better.  A thin coat held, without the glue a thick coat did not.  W hat I cant understand is why there are blisters now and on only some of the pieces.

 

Niel,  Thanks for looking at the program.  I guess I was tired when I calculated the firing time.  I was off by about 2 hours.  I plan to fire some test pieces tomorrow with the same glaze.  My plan is to us the cone setting with a med ramp.  The reason I was doing a slow cool was because most of the pieces in the kiln were being refired due to blistering.  All the blistering did disappear but many of the pieces now have pinholing and the color is unattractive. 

 

I don't like not knowing why the refired pieces have the pin holing.  I am worried this will be a repeat problem as I like this glaze.

 

Thanks again for your help. 

 

Is this a single glaze, or overlapped glazes? If it's two glazes, then they just don't play nice together. If it's a single glaze, to me it looks like it's over fluxed and needs more alumina or silica in the mix. Can you post the recipe?

 

I get that you want to slow cool, but going 35F/hr is excessively slow, and at the point in the firing that you're going that slow (1900F), the glaze has already stiffened considerably and you're not getting any benefits as far as helping the pinholing. Try keeping it simple and just do a one step slow cool at a rate of 150F/hr to 1500F.

 

If you want to put down cone 6 then add another 20 degrees to the peak temperature. But based on the fluidity of your glaze that may not be necessary.