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How to Adujst my kiln sitter


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I just did a bisque fire to 05 and the witness cone did not bend all the way over. They pryro bar was bent to a perfect 90 degrees. (I can't find the picture but will add it later if I need to). I am going to do a Cone 6 glaze fire this weekend and am worried that I will not get all the way to 6 with the sitter set up the way it is. I used the proper firing gauge to calibrate it and have a 1/16 of an inch between the weight and the hook. I was wondering if I need to make this space smaller to get a little more heat? does this make sense? Any advice is greatly appreciated. Thank you.

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If you are using the triangular mini cones in the sitter, you can shift it slightly in the sitter so the rod is resting on it closer to the fat end. That will cause it to fire slightly longer before releasing the claw. Put witness cones on the shelves and watch them through a peep so you know what is actually happening inside.

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What you are looking at is the very reason why the kiln sitter was designed as an overfire safety device, not a control device. It was never designed for the cone in the sitter to invariably and exactly match witness cones on the shelf. It is true that some potters use the sitter as if it is an infallible control device - e.g., a bent 05 cone in the sitter must mean the kiln fired to ^05 - but most of them don't know what cone their kiln actually fired to because they don't use proper witness cones in the kiln. Those who do put witness cones on the shelves can tweak the sitter to release at a different time, but that particular adjustment may or may not work for both bisque and glaze firings. The only way to know if your sitter that dropped at approximately the right time for the ^05 bisque firing is also going to drop just right for the ^6 glaze firing is to try it.

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Put the witness cones in front of a spy/peep hole and check that you can see them before starting the kiln. Wearing kiln safety glasses to protect your eyes monitor the witness cones towards the end of the firing. If the witness cone isn't as bent as you want it when the kiln sitter trips off then you need to lift the trip arm up about 45degrees and press the white button to restart the kiln. Check the witness cone about every 10 minutes until it is bent how you want it then press the trip arm all the way down to shut off the kiln. If you find the reverse is happening with a cone 6 firing and the witness cone is overfiring then stop the firing by pressing down the trip arm. 

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14 hours ago, Dick White said:

What you are looking at is the very reason why the kiln sitter was designed as an overfire safety device, not a control device. It was never designed for the cone in the sitter to invariably and exactly match witness cones on the shelf. It is true that some potters use the sitter as if it is an infallible control device - e.g., a bent 05 cone in the sitter must mean the kiln fired to ^05 - but most of them don't know what cone their kiln actually fired to because they don't use proper witness cones in the kiln.

I respectfully disagree. The Sitter was designed to shut off at the proper temp once it has been calibrated. While the Kiln sitter manual says that witness cones are the most accurate method, it specifically says that using witness cones in combination with the  Sitter is optional, and only necessary for calibrating the device. And every kiln manual I've ever seen also assumes that the Sitter will be the primary shutoff device.

I totally agree, however, that it's not necessarily going to 100% match the fall of a witness cone. But most glazes have a wide enough firing range that the small variations one might get won't be a problem. @Oddoneout I wouldn't make any changes to your set at this point. The witness cone is really, really close to being all the way down, and you may find different results at cone 6.

 

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Well, I was aiming for a Cone 6. There is a 5,6,7. Looks over fired as does the sitter bar. 
 

also my cone 6 white glaze ran everywhere. I think this means it was over-fired. 
 

what to do now?  I think it would be ok except for the cone 6 glaze white glaze. And yes I will be chipping away at a few of my shelves ( they did have fresh layers of kiln wash on them)

65F7B5A4-D350-4395-AD15-C9C11FA1338D.jpeg

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Not sure what you are shooting for but that looks to be a near perfect cone six actually. My guess is the white runny glaze is really not cone six in your application. The cones pretty much clearly show that.

Your witness  cones to me show that you fired to a near perfect cone six. Maybe just ever so slightly higher but a degree or two heat work in 2000 is spot on in my view.

When we formulate glazes they always work acceptably in a range and have their own property of movement. Some glazes are designed to move, some you can count on not to. some can be layered, some cannot. Most perform reasonably well within a cone or so  of their rating. My take, the white glaze is cone five or less, or potentially  somehow is a lowfire glaze. Is it  a commercial glaze or one that was mixed from a recipe?  If a recipe, post it’s components.

Edited by Bill Kielb
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9 hours ago, Bill Kielb said:

Not sure what you are shooting for but that looks to be a near perfect cone six actually. My guess is the white runny glaze is really not cone six in your application. The cones pretty much clearly show that.

Your witness  cones to me show that you fired to a near perfect cone six. Maybe just ever so slightly higher but a degree or two heat work in 2000 is spot on in my view.

When we formulate glazes they always work acceptably in a range and have their own property of movement. Some glazes are designed to move, some you can count on not to. some can be layered, some cannot. Most perform reasonably well within a cone or so  of their rating. My take, the white glaze is cone five or less, or potentially  somehow is a lowfire glaze. Is it  a commercial glaze or one that was mixed from a recipe?  If a recipe, post it’s components.

Bill,

thank you. I thought that the witness cone should only fold over to the top of the base, hence why I thought it was over fired. 

the glaze is from my local ceramics shop, it is their house brand and is 04-6. 
 

Over night I was thinking I should try firing at cone 5. 

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4 minutes ago, neilestrick said:

That cone is barely over fired, not enough to mean the difference between a glaze being fine and running off the pot. I'd take a look at the glaze recipe and stiffen it up. I think your cones are close enough that adjustment to the sitter isn't necessary.

Thank you Neil, with this info I am going to leave my sitter as is. 
 

as for my glaze, I wonder if it is too thick. I mixed (it came dry) per the instructions provided. It is thick. I am keeping notes on everything and have reached out to my local shop that mixes it and asked, we’ll see what they say. 
 

if I continue to have glaze trouble I will start a thread in the appropriate forum. 
 

thank you to everyone that has offered info/opinion/help!!

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47 minutes ago, Oddoneout said:

their house brand and is 04-6. 

That would be a fairly large range for a glaze although there are some lowfire glazes that work at midfire temperatures. I would check and see if that is a typographic error on their part and they did not mean 04-06 firing range.

Orton witness cone firing positions below. Once the cone reaches the three o clock position it literally is within a few degrees from its fired cone value.

74F843D3-2216-4DDB-87E2-D4AEB1BA4F58.jpeg

Edited by Bill Kielb
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2 hours ago, Oddoneout said:

I thought that the witness cone should only fold over to the top of the base

For self supporting cones, yes, but like others have said there isn't much difference between that point and tip touching shelf.  Re you runny white glaze, if you have a bucket of it it would be worth testing it with some EPK (Edgar Plastic Kaolin) to slow down the running. EPK is a common source of alumina in glazes, it can be used to stiffen up fluid glazes by adding a small amount of it. It could save you doing a separate lower firing for just that glaze and/or underfiring your clay. Seattle Pottery Supply has a couple glazes they sell as ^04 - ^6, a friend of mine uses it overtop of other glazes for some lovely runny effects at ^6.

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