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Alexis K

Kiln Sitter Shut Off Before Full Fire

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Hi everyone!

 
I am an art teacher and am new to the firing process. I have the AMACO Standard Economy Electric Kiln (EC-55). kiln. The kiln sitter I have is the model LT-3 (I attached a picture of the kiln sitter that I have).

I did a bisque fire last night with the pieces that were made from lowfire earthenware clay. The clay can be fired from 06-04. I used cone 05 and and set the timer on the kiln sitter to 12 hours. This morning I walked in and the dial seems to have stopped at 6 hours instead of firing for the full 12 hours. I am not sure what the problem could have been.

Do you think I should re-fire the pieces for an additional 6 hours with a new cone? I don't know if they would be okay to glaze or not because it did not fire for the full amount of time. 

 
Thanks!

post-1594-12722496040703.jpg

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Hi Alexis!

That kiln sitter looks just like the unit on my old Skutt (new in 1988). The drop switch - as I'm sure you a'ready know - is actuated by the softening of the cone.

Typically, the timer is set to a value greater than the expected firing time; if the drop switch fails for some reason, the timer will shut down the unit*. 

Hence, either will shut you down - both have to be on to run, but both don't have to be off to shut down, make sense?

 

The timer can "get" you either way! If

  a) it's taking longer than expected to reach the desired cone, firing incomplete, else

  b) the drop switch fails for some reason, overfired.

 

*Please don't depend on the timer to shut down an unmonitored kiln!

...suggested that kiln sitter equipped units be closely monitored (I'll be monitoring ANY kiln)!

Pyrometers aren't terribly expensive - provides a continuous reading (be sure to compare against cones).

Place cone packs in your kiln - after a few firings, you'll have it all down!

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Thanks! I am still confused as to whether or not I should fire the pieces again and if they are indeed under fired or over fired.

When I walked in, the silver drop switch was down, and the dial was at the 6, which I assume means that it fired for only 6 hours. The temperature was almost at 0. I opened the kiln to check the pieces and they are not light pink. They still look white.

Do you think I should fire the pieces again with a new cone? Or, would they be okay to glaze from only being fired for 6 hours?

Sorry, I am very new to all of this!

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If the kiln sitter shut the kiln off because the sitter cone bent then yes your kiln fired as expected. No, you don't need to re-fire the pots. No, it doesn't take the full 12 hours to fire to cone 05 unless you spent a very long time on low or medium setting. If you spent little or no time on low or medium settings then yes it's possible to fire to cone 05 in 6 hours. When you unload the kiln have a look at the cone in the sitter, it should be sagging in the middle. Like Hulk said put some cone packs or self supporting cones in the kiln on each shelf to verify how it's actually firing. This is important, especially for the glaze firing. 

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This is how my cone looks. I put it next to the diagram in the book. My main concern is that the pieces are still white. Doesn't this indicate that they are not fully fired? I thought the pieces had to be light pink after the bisque fire.

Screen Shot 2019-01-03 at 12.56.42 PM.png

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Ive found that the weight of the sitter "bar" can cause a baby cone to drop early. Ive also had baby cones not drop by the time my visual cone pack tells me the firing is done. The sitter cone is used just as another fail safe (same as timer on sitter) to prevent overfiring. I would not rely on the kiln sitter cone as a determination of proper temp. Use a visual cone pack for this, and be there while the kiln is firing to ensure you reach that point, and turn the kiln off when done.

The color of the work is not a determination of proper temp either; the multitude of clays that go into each clay body will have a drastic impact on the color of the fired clays. You can have properly fired bisque color everything from dark brown to light white.

If you havent unloaded the kiln yet, put another kiln sitter cone in the kiln, put a visual cone pack in there too, and fire again. "firing for another 6 hours..." does not get you where you want to be. I could fire for 30 hours at 1,000* and not bisque properly. Time is only a part of the equation in achieving a proper cone temperature.

Heres my suggested firing for potentially "slightly" damp student work; and I mean bone dry, but maybe still some moisture. Night before, crack kiln lid 2-3", and turn bottom switch to low. Next morning, lower lid-wait 2 hours. Turn all switches to low-wait 3 hours. All switches to medium-wait 3 hours. All switches to high until visual cone pack indicates proper temp achieved.

You will have to "add" time to your timer as you're firing the next day as otherwise it will shut the kiln off prematurely. Also, if sitter shuts kiln off prematurely, lift the trip arm back up, push button back on, and gently lower the arm so as to not trip the switch again. Monitor the cones/kiln until visual cones are properly achieved. Dont rely on the timer/switch at this time because you've bypassed the switch, and if left to the timer it could seriously overfire.

Even computer controlled kilns need to be monitored during firings; dont rely on technology to keep your studio safe. Stuff goes wrong all the time!

Edited by hitchmss

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If the pots feel bisqued you are good to go. That cone looks fired . What does look funny in your photo the counter weight swing arm is still stuck in the up position and its not under the rod latch???.Mine will not stay up like yours in photo without falling or being under rod latch.

Meaning it did not drop and shut off kiln when cone melted

On further looking it looks to be up but not HOOKED under the rod holder.

Do you understand how to set the Dawson sitter?Did you change this after firing before taking the photo? or is this how it looked when you arrived and kiln was off?? we need to know these details to help.

You lift up counter weight on outside of kiln with the  rod up on the outside of kiln you catch the latch on rod holder over the counterweight and put cone on inside under rod  in middle of the two inside pins . Let go of rod latch -set timer to 12 hours push inside button in counter weight swing and kiln is on and ready to go.

You can find instructions online if these are not clear.

Ceramics is fires to cone temps not how pink or white they look. You can also tell by ring and feel or water absorption if they are  bisque enough.This is a learned experience .

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Mark,

Yes I was instructed on how to set the sitter prior to the firing, and I did a test fire last year. The picture of the sitter is one that I found off of Google. The picture of my cone fired on the pamphlet was how I found my cone when I came in and the kiln was off with the switch down. I took it out of the pins to take the picture! I spoke to someone else who says the color from the bisque fire depends on the clay that is being used. He said that not all clays will have a light pink color after bisque fire. I think I am going to have my students glaze the pieces tomorrow and then I will go a glaze fire to see how it turns out. I was initially confused because I did not know If i needed to do another bisque fire. The cone seems to tell me that the pieces were fired, and I assume it only needs to be fired for 6 hours.

 

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Since many folks use different color clays they can change color to different colors in bisque. For example I fire porcelain and its white going in and what coming out of bisque. Stonewares can also go light to greys to pinks so color is not a good guide. The clay going in it fragile and has no ring to it. Coming out of a 06 bisque it will have a better ring and feel harder-you cannot say gouge it with your fingernail after bisquing where you can when its green before a bisque fire.. After a few fires this will all be second nature to you.

good luck

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7 hours ago, liambesaw said:

Was the cone wet? My cones usually look glassy white when done, that one looks like it went without being fired

I think the color of the fired mini-cone varies with cone #.  I fire ^04 bisque, and those are always dark 'brick red' when done.  The ^5 & ^6 I use for glazes come out glassy white.

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,)

Set up cone packs for each shelf, given you have cones for that; at minimum, set a target cone up on each shelf.

Can you get your hands on a pyrometer?

Below is what I'm using (Aardvark has a decent price for that, given the thermocouple is a decent K type ...which it be that). Mine reads a bit high - dial in against your cone behavior.

Firing is time and temperature; both are key.

pmeter.JPG

Edited by Hulk
source of

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I use mini bars( I like the best -more accurate) , and junior cones (using them up) they are all cone 08 (my bisque cone temp) and they turn red .They start out as dull red then get to be a darker brick red after fired.I only bisques in the electrics.And rarely at that but I have one 95% loaded and waiting for a few pots to  fill it then fire it.

Edited by Mark C.

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alexis, this is the most complete question and response i have read on the forum in a long time  and  you have gotten correct information from everyone who responded.   i would like to add just a thought or two. 

if you think about the bisque firing as just allowing the work to become hard enough to handle through the glazing step, you might realize that it is not really necessary for the clay to reach a certain temperature or time in that first firing.   i know this sounds like heresy but think about the hundreds, thousands of years that pottery has been made with only a single firing.   yes, there MIGHT be a small problem with not getting all the way to the cone you expected but that would be a small problem.   if you think the ware is too soft and will absorb the glaze coating too thickly, dampen the pieces before applying the glaze.   if you are brushing glaze try to get the moisture content just right, so the brush does not stick to the piece within an inch or two of touching the pot.    so, no, you do not necessarily need to refire to the lower temp, just fire slowly to the mature temp after glazing the work.

the next time you buy cones, ask for minibars.  they come in two shapes, one is a triangle that is even all along the length and the other is a thinner square shape.  they are easier to use and you do not have to worry about getting the usual kind absolutely centered on the posts.  the triangular ones come stuck together and sometimes break before separating so i prefer the square bars.

have fun with the kids and enjoy the journey.

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12 hours ago, oldlady said:

alexis, this is the most complete question and response i have read on the forum in a long time  and  you have gotten correct information from everyone who responded.   i would like to add just a thought or two. 

if you think about the bisque firing as just allowing the work to become hard enough to handle through the glazing step, you might realize that it is not really necessary for the clay to reach a certain temperature or time in that first firing.   i know this sounds like heresy but think about the hundreds, thousands of years that pottery has been made with only a single firing.   yes, there MIGHT be a small problem with not getting all the way to the cone you expected but that would be a small problem.   if you think the ware is too soft and will absorb the glaze coating too thickly, dampen the pieces before applying the glaze.   if you are brushing glaze try to get the moisture content just right, so the brush does not stick to the piece within an inch or two of touching the pot.    so, no, you do not necessarily need to refire to the lower temp, just fire slowly to the mature temp after glazing the work.

the next time you buy cones, ask for minibars.  they come in two shapes, one is a triangle that is even all along the length and the other is a thinner square shape.  they are easier to use and you do not have to worry about getting the usual kind absolutely centered on the posts.  the triangular ones come stuck together and sometimes break before separating so i prefer the square bars.

have fun with the kids and enjoy the journey.

Thank you!! :)

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