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Nelly

Computerized kiln monitoring?

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Dear All,

 

I have just done another bisque fire. I put 04 kilns on the shelves. Self-supporting large orton cones.

 

I programed the kiln for a slow bisque (i.e., to take up to 13 hours).

 

When the temperature was hovering at 1940 degrees I checked the cones and found they were down. Completely down.

 

Thus, I turned off the kiln.

 

Here is my question:

 

1. Cone 04 by the Orton charts says a temperature of 1956 degrees.

 

2. I use cone 6 glazes.

 

By reaching this temperature (i.e., as evidenced by my cones being down around their ankles) have I over fired the pieces? Will I run into difficulty with glaze sticking??

 

Is 04 a standard temperature to bisque to or do others do something else? Please know my kiln is a new one and I simply pushed the slow bisque option on the panel. It is a cone art. I was firing large platters and wanted the slow bisque to ensure really good removal of water despite being convinced they were absolutely bone dry by putting them against my cheek.

 

What temperature do others use? Would this temperature of 1940 be considered over fired for cone 6 clay/glazes?

 

Nelly

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Nelly;

I had a Cone Art kiln for a long time, but not a computerized one. I bisque at around cone07/06. This should be hot enough. A bisque should take no more that eight hours. you probably will be O.K. with your glazing, but I would say that cone 04 is a bit high for a bisque. When bisquing, I am on low for two hours, then medium for an hour, then on high until the sitter shuts her off. I make thrown functional pottery, so I don't worry about things being too thick.

TJR.

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Guest JBaymore

An important concept to understand here...... cones do not measure temperature. Cones react to the combination of heat energy and time. So the amount a cone bends is dependent on what is commonly called "heat work". It is the application of heat energy over time......usually gauged by rate of temperature increase.

 

Generally speaking, the faster the kiln's temperature increase, the higher the end point temperature for a given cone to bend til the tip is equal to the base will be. The slower the temperature rise, the lower the end point temperature.

 

That "13 hour bisque program" you mention....... does it specify the end point cone that it is designed to achieve?

 

The appopritate bisque temperature of any given clay body is determined by a lot of things. There is no one "correct" temperature. One aspect is that all of the necessary chemical reactions that need to take place in the body go to completion. Mainly for bisque, this involves driving off the chemically bound water in the clay crystals (making it now "ceramic", not clay), burning off the carbonaceous material contaminating the clays, combusting sulphur compounds to sulphur di and tri oxide, and converting some compounds like certain carbonates to the oxide forms.

 

Then there is the absorbency factor for glaze application. Differnt people desire different levels of absorbency to the bisque depending on the way they apply glazes and the particular glazes they use. So there is a "personal" factor involved there too.

 

The best way to tell if the clay is too dense for how you handle your glazes and the viscosity of the mixtures you use is to try it.

 

best,

 

.....................john

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An important concept to understand here...... cones do not measure temperature. Cones react to the combination of heat energy and time. So the amount a cone bends is dependent on what is commonly called "heat work". It is the application of heat energy over time......usually gauged by rate of temperature increase.

 

Generally speaking, the faster the kiln's temperature increase, the higher the end point temperature for a given cone to bend til the tip is equal to the base will be. The slower the temperature rise, the lower the end point temperature.

 

That "13 hour bisque program" you mention....... does it specify the end point cone that it is designed to achieve?

 

The appopritate bisque temperature of any given clay body is determined by a lot of things. There is no one "correct" temperature. One aspect is that all of the necessary chemical reactions that need to take place in the body go to completion. Mainly for bisque, this involves driving off the chemically bound water in the clay crystals (making it now "ceramic", not clay), burning off the carbonaceous material contaminating the clays, combusting sulphur compounds to sulphur di and tri oxide, and converting some compounds like certain carbonates to the oxide forms.

 

Then there is the absorbency factor for glaze application. Differnt people desire different levels of absorbency to the bisque depending on the way they apply glazes and the particular glazes they use. So there is a "personal" factor involved there too.

 

The best way to tell if the clay is too dense for how you handle your glazes and the viscosity of the mixtures you use is to try it.

 

best,

 

.....................john

 

 

Dear John,

 

Thank you for the cone explanation and a reminder of all the related factors that go into doing a bisque fire. On the advice of a friend, I did turn the kiln off when he said I would get bloated pieces if the temperature was too high and given the fact my cone had melted to its ankles.

 

I will likely glaze fire these pieces next week and will keep you posted about the adhesion and fit of the glaze. Right now, I am working with a collection of clay bodies that are all cone 6. In short, I am using up scraps. This too, will be another variable.

 

So, I will wait and see and keep you posted. I think I will also call Tuckers to find out the end point of the cone as you suggested after firing. This piece of information will be useful in trying to ascertain their expectations of their kiln versus my experience. To me, when a cone is right down, it means you are over firing. But perhaps, as I think you suggested, sometimes a kiln schedule will have this in mind in the climb.

 

Given that mine was supposed to be a slow climb to temperature, it is interesting how the middle cone went down so low. Thank you sooo much for taking the time to reply.

 

Nelly

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When you talk to the folks at Tuckers, ask them if you might need to adjust the thermocoupler offset programmed into your electric controller. If your thermocouplers are covered with a thin ceramic tube, the manufacturer programs an offset into the firing program to account for this. Because the thermocoupler is not exposed directly to the heat due to the covering, its reading needs to be adjusted to account for the difference. I have an L&L kiln, still relatively new, that tends to fire "hot" . . . meaning when I put cones in to check firing temperatures, they tend to go more towards flat. I have one ^6 clay body that is more likely to bloat in my kiln than at the studio where I also fire. The studio kiln has many miles on it and tends to fire "cooler". An adjustment to the thermocoupler offset is likely more important to your glaze firing than bisque firing.

 

You should not worry about bloating when bisque firing a ^6 clay body to ^04 or even ^03. Bloating will occur when you over-fire . . . which in your case could be a "hot" ^6 or higher (^7).

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When you talk to the folks at Tuckers, ask them if you might need to adjust the thermocoupler offset programmed into your electric controller. If your thermocouplers are covered with a thin ceramic tube, the manufacturer programs an offset into the firing program to account for this. Because the thermocoupler is not exposed directly to the heat due to the covering, its reading needs to be adjusted to account for the difference. I have an L&L kiln, still relatively new, that tends to fire "hot" . . . meaning when I put cones in to check firing temperatures, they tend to go more towards flat. I have one ^6 clay body that is more likely to bloat in my kiln than at the studio where I also fire. The studio kiln has many miles on it and tends to fire "cooler". An adjustment to the thermocoupler offset is likely more important to your glaze firing than bisque firing.

 

You should not worry about bloating when bisque firing a ^6 clay body to ^04 or even ^03. Bloating will occur when you over-fire . . . which in your case could be a "hot" ^6 or higher (^7).

 

 

Thank you also for your reply. I will ask about this tomorrow. It has happened twice so it could be an adjustment problem. Glad you think there will be no bloating. This is reassuring. I did look up "bloating" in ceramic terms. It seems it refers to gas pockets that enlarge and can make your piece wonky. While I am usually wanting to open the kiln as quickly as possible (i.e., oven temperature), I have no urgency about this and will look at it tomorrow in the late afternoon. I will check this out though before I glaze fire next weekend and get back to the group on my finished products. I will also be watching the cones more carefully this time to watch for bending. I hope it is something simple like this thermocoupler adjustment. Just seems funny for me that after all the time I spend watching cones bend that this would happen. But I will pay heed to all advice and let you know what Tuckers says. Why oh why can't I just press a button and this fancy computerized kiln just work the way I thought it would. I hope this is going to be as simple as my GPS was in terms of eventually understanding how it works.

 

Nelly

 

Nelly

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Often the thermocouples will read differently at high temperatures than at lower temperatures. You can adjust the offset for a specific cone if needed. I wouldn't be too concerned about the bisque, though. The glaze temp is the important one. My smaller kiln fires a little bit hotter than my large one, so I adjusted cone 6 to be a little bit cooler. On my large kiln, the bottom center is just a bit cooler than the rest, so I adjusted the thermocouple offset for that section to fix the problem. In both cases, 10 degrees did the trick.

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Often the thermocouples will read differently at high temperatures than at lower temperatures. You can adjust the offset for a specific cone if needed. I wouldn't be too concerned about the bisque, though. The glaze temp is the important one. My smaller kiln fires a little bit hotter than my large one, so I adjusted cone 6 to be a little bit cooler. On my large kiln, the bottom center is just a bit cooler than the rest, so I adjusted the thermocouple offset for that section to fix the problem. In both cases, 10 degrees did the trick.

 

 

Dear Neil,

 

Wow!! That was it. 10 degrees??? It sounds so simple. I will let the group when I speak to the company. That really does sound easy though.

 

Nelly

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10 degrees is a lot in cone terms. The difference between cones at mid range temperatures is only 30 degrees. There are a lot of adjustments that can be made to your kiln to get things just right. Spend some time with your manual and it will ease a lot of frustration and uncertainty. You can't really screw things up that much. Worst case you just reset everything back to factory settings.

 

Personally, I have never put cones in my kilns. I go entirely by how the glazes look. If they look good, I'm happy, whether it was a true cone 6 or not. It saves me a lot of time and frustration that way.

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10 degrees is a lot in cone terms. The difference between cones at mid range temperatures is only 30 degrees. There are a lot of adjustments that can be made to your kiln to get things just right. Spend some time with your manual and it will ease a lot of frustration and uncertainty. You can't really screw things up that much. Worst case you just reset everything back to factory settings.

 

Personally, I have never put cones in my kilns. I go entirely by how the glazes look. If they look good, I'm happy, whether it was a true cone 6 or not. It saves me a lot of time and frustration that way.

 

 

Dear All,

 

I have now unpacked the kiln and all turned out perfectly. No unusual bloating noted at this point. Have been busy but will contact Tuckers to get a better idea of what is happening. When I did remove the shelves and saw the cones what I can say is that when I placed the self-supporting cone one of my wareboards it bent below the level of the shelf. Thus, it was not around its ankles but rather puddling on the floor. It did not stick but I have never seen a cone go so low before. I am used to the side bend look. But do know I will speak with the company and make 100% sure I am doing everything exactly the way it should be done.

 

The manual, like so many teaching sources on the more technical aspects of ceramics is somewhat beyond my level.

 

The last time, I used Frog Pond's firing schedule adapted to this kiln and it seemed to work out perfectly. So maybe I am doing something wrong or there is a calibration issue.

 

Thank you again, each of you for your thoughtful responses.

 

Nelly

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Get a magnifying glass and check the numbers on your cones to see if you are using the correct ones. And look at a cone chart to check the temperatures of the cones you are using.

 

 

 

 

 

That is a good point too. Errors like this can and do happen.

 

Nelly.

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Nelly;

I had a Cone Art kiln for a long time, but not a computerized one. I bisque at around cone07/06. This should be hot enough. A bisque should take no more that eight hours. you probably will be O.K. with your glazing, but I would say that cone 04 is a bit high for a bisque. When bisquing, I am on low for two hours, then medium for an hour, then on high until the sitter shuts her off. I make thrown functional pottery, so I don't worry about things being too thick.

TJR.

 

 

TJR,

How long do you generally keep the kiln on high for? I was bisquing at low for 6 hours to make sure everything was dried out, medium for 2 hours and high for about 4 hours, and was doing it by the feel of the pottery, as I couldn't see the cones through the peepholes and the kiln sitter isn't working. Thank you,

Nancy

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