Firing Schedule - Fine tuning your electric kiln controller

[Brent Farler]

 I am working with an Orten controller on my electric kiln.  In spite of low use (<30 firings) my thermocouple doesn't appear to read very accurately.  The automatic cone fire programs consistently overfire.  

I am trying to get the adjustments just right to get the combination of a good soak, slow cool and actually hitting cone 6.  

My teacher really recommends I soak for 30 minutes and cool at 90 degrees and hour.  If I set my controller to fire cone 6 with these parameters it will flatten a 7 cone flat as a pancake not to mention flattening all of my colors along with it.

I fiddled with a few firings and found a cone 4, slow ramp, with 30 minute soak, Thermocouple offset of -10 degrees and 90 degree cool down would put a cone 5 over and leave my cone 6 at about 2:30.  Colors looked pretty good but my teacher is telling me the clay body feels underfired (using a cone 6 stoneware).  I would like to hit the cone 6 on the nose but not sure which factor to tweak.  My controller manual isn't much help since it pretty much only gives the conversion chart for what looks like a no soak firing and my temp is unreliable.

Thoughts?

[Jeff Poulter]

Type S is typically what is used.  I got mine direct from Bartlett.  I lied, it was $209.00, not $175.00.  That must have been the one before & I can't find it in my e-mails.  jhp

[Norm Stuart]

Thanks, Jeff. Just what I needed to know.

[Brent Farler]

I have a Paragon Kiln, they sold me a type S with Ceramic protection tube and new wires (the wires to the controller have to match the thermocouple) for $200 plus shipping. Make sure what you are getting includes all three as separately they are more expensive.  

My K was semi-predictable for a while, I was using the TCOS to adjust but then I would get random over and underfirings.  

BTW, another firing and we are down to calibrating the cone and soak within 2 degrees.  Joy - I used to be happy to just get somewhere between a 5 and not too much bend on seven.  Now I am getting flat 5, 5 o'clock 6 and barely a bend on 7.

[Brent Farler]

BTW, my type K thermocouple was reading quite nicely for bisque firing (Orten cones matched to the Bartlett Cone fire program with the TCOS adjusted to previous results)  but not cone 6 where it read unpredictably.

Brent Farler said:

I have a Paragon Kiln, they sold me a type S with Ceramic protection tube and new wires (the wires to the controller have to match the thermocouple) for $200 plus shipping. Make sure what you are getting includes all three as separately they are more expensive.  

My K was semi-predictable for a while, I was using the TCOS to adjust but then I would get random over and underfirings.  

BTW, another firing and we are down to calibrating the cone and soak within 2 degrees.  Joy - I used to be happy to just get somewhere between a 5 and not too much bend on seven.  Now I am getting flat 5, 5 o'clock 6 and barely a bend on 7.

[George Lewter]

I agree with Neil. Type K probes come standard on most Cone 8 kilns and many Cone 10s. They do oxidize over time, but they are good enough for most potters. If your program temperatures correspond closely to the way your pyrometric cones bend, then the thermocouple is doing its job.  Norm, if you got 30 months out of yours, as often as you fire, your probe did great, went beyond the call of duty, and deserves a funeral with full honors. You might consider replacing them once every 15 months, rather than having them fail. I check mine visually every firing and replace when it looks like the corrosion has eaten about a third of the wires' cross section. Protective covers slow the corrosion, but they also slow response time. 

It wasn't that long ago that most potters dug their materials out of the ground, mixed in ashes and a few impure colorants, and the only real-time temperature measurements came from eyeballing the kiln interior, and pulling out draw rings. Yet the Sung and Ming potteries in China produced magnificently beautiful pieces in roughly the years 960 - 1644 AD.

The pursuit of totally predictable outcomes is great for toilet, tile and dinnerware manufacturers, but the happy accident is what I live for. I don't want reagent grade chemicals. And I don't care if my kiln doesn't fire with scientific accuracy and precision. It's just a glorified fire pit, and control is the greatest illusion of all.

[Neil Estrick]

Thermocouples should never be used to the point that they fail. That's when you run into real accuracy problems. Same goes for the elements. Elements that burn out have been firing inefficiently for a long time, and you'll often do more brick damage replacing fried elements.

I have had several customers who were unhappy with their kiln's performance when they hooked up a PC to their kiln controller. The PC allowed them to see the variability between thermocouples or between firings, and they got angry about the lack of precision in their kiln, even though it had been there all along and the results in the pots hadn't changed. If the pots look good, then the firing is precise enough. When firing with cones in gas kilns, we generally accept 1/2 cone or more difference. But that doesn't seem to be the case with electric kilns for some reason. With well formulated glaze, a 1/2 cone isn't noticeable.

I think the biggest problem people have with digital electric kilns is that they expect them to have less variability because they are digital, when in fact the exact opposite is true- they have more variability and less accuracy than firing with cones, no matter what type of thermocouples you have. The programs in digital kilns are simply approximating cones. So even if you manage to get your temperature readings ultra-precise, you still won't have the same ability to measure heat work as you will with cones.

Type S thermos are great for people who really do need more accuracy, like crystalline glazes, but the for the average user they are overkill. With well formulated glazes and a calibrated kiln, type K's will work for most everyone. That is why kiln manufacturers use them. But you have to be willing to put in a little bit of work getting your kiln set up just right. They are not usually plug and play.

Never buy thermocouples from anyone but kiln manufacturers, because they have tested them to find those that work the best. Avoid eBay and such.

[Norm Stuart]

We'll test out the Type-S we get from Bartlett with Witness Cones as we did the original Type-K.

It looks like Bartlett would rather have us send the CPU back to them to make the thermocouple change. I'm pretty sure it needs an update to the EPROM, in addition to the change in the "Hidden Menu". They have an indexing error in the original EPROM which was easy to work around but kind of silly.  We've always needed to choose the next lower cone to achieve the correct Witness Cone - regardless of what cone we're firing to.

The update will also change each user program from 8 step to 16 step.

I've never been particularly impressed with how much Cress knows about their kilns. Bartlett has always been the source to go to.

[Brent Farler]

Bartlett makes the boards for all these guys.  When you get the type S make sure it either comes with new pair of wires, the old K wires will not read properly.  Don't know why but it could be related to the type of metal required to match up with the type of metal in the thermocouple since it is the difference between two metals that creates the current you don't want the heat at the thermocouple connection to your board to also be creating a current as well.

George, I only partially agree about the unpredictability being a positive part of the process.  Guess that is why my wife is the better artist and I am the better technician.

[Jeff Poulter]

Yes, the wire will have to match since you are changing the metals which supply the current to the controller.  It's nice when they give you an upgraded board in the deal.  Besides being able to do a 16 segment program, you should be able to marry a cone fire to a user program as well.  On later boards it's usually just a jumper change to go from S to K or visa versa.  Without changing the wire & the internal configurations, you will be feeding erroneous signals to the controller & really mess things up.  It is very nice to have some form of serendipity in our work, but even controlling all that we can, there will always be some of that involved in any firing.  The ability to control some part of the firing is always a plus and makes it easier to produce a desired effect more than just once.  Yes, through the ages they have produced some absolutely beautiful pots, many of which that can't even be produced today with all our technology.  However, with a little digging(pun intended) you can find the huge piles of pots & shards that didn't make the grade.     I know that type K is pretty standard in most kilns.  Mainly it's a monetary thing.  A lot of hobbyists just do earthenware & it works perfectly.  A lot of these kiln manufacturers say their kilns will go to ^10.  I ask , how many times & with how many dragons breathing on the underside of the kiln?  You can't change physics.  You need a certain amount of watts for any given amount of space to raise the temperature to a certain level.  How you do that & how you monitor that is up to you.  That's why there are umpteen kiln manufacturers, so just do your homework & make sure you kiln & accessories fits your needs.  jhp

[Norm Stuart]

George, I appreciate your perspective and I've heard similar comments from other ceramicists, but I'd rather be the driving-force creating the beautiful unexpected surprises - thus knowing how to recreate it.

I understood how many variables went into ceramics when I watched an episode of UK Antiques Roadshow when they visited the Wedgwood factory.

They read Josiah Wedgwood's original kiln journal when he and his mentor were developing their first "Queensware" for the British Queen consort Charlotte of Mecklenburg-Strelitz. After pages and pages, finally Trial 137 SUCCESS!

Better to stand watch and use witness cones than use an unreliable cone fire. I've found our Bartlett V6-6F Controller with a Type-K thermocouple in close agreement with the occasional witness cone I add to a firing. But I'm up for the small extra cost to achieve a tolerance of +/- 2 degrees.

The bottom line for us is the controller has needed to go back to Bartlett to get the EPROM flashed with a program update ever since we bought the kilns, so they'll switch out to a Type-S thermocouple at the same time.

George Lewter said:

I agree with Neil. Type K probes come standard on most Cone 8 kilns and many Cone 10s. They do oxidize over time, but they are good enough for most potters. If your program temperatures correspond closely to the way your pyrometric cones bend, then the thermocouple is doing its job.  Norm, if you got 30 months out of yours, as often as you fire, your probe did great, went beyond the call of duty, and deserves a funeral with full honors. You might consider replacing them once every 15 months, rather than having them fail. I check mine visually every firing and replace when it looks like the corrosion has eaten about a third of the wires' cross section. Protective covers slow the corrosion, but they also slow response time. 

It wasn't that long ago that most potters dug their materials out of the ground, mixed in ashes and a few impure colorants, and the only real-time temperature measurements came from eyeballing the kiln interior, and pulling out draw rings. Yet the Sung and Ming potteries in China produced magnificently beautiful pieces in roughly the years 960 - 1644 AD.

The pursuit of totally predictable outcomes is great for toilet, tile and dinnerware manufacturers, but the happy accident is what I live for. I don't want reagent grade chemicals. And I don't care if my kiln doesn't fire with scientific accuracy and precision. It's just a glorified fire pit, and control is the greatest illusion of all.

[Robert Coyle]

I fire to cone 6 but the Skutt kiln I have  is (supposedly) rated for cone 10. I did a full bore test fire on the empty kiln (slightly used) when I first got it. By the time it reached cone 7 temperature the curve had fallen off to

less than 75 deg F/hour. This is as far as I took it. Seem like this would have a hard time going to cone 10. The kiln had only been fired a dozen or so times before. Sounds like I need more dragons.

[Jeff Poulter]

Hi Robert,

    Which Skutt is it?  My little KM-818 will go to ^10.  It doesn't like it, but it does it better since I had Euclids make up some beefier elements.  If you beef them up too much, you may have to redo your breaker & wiring and the relays may not like it. Heavier gauge elements last longer, but cost more, cause you're using more wire in each element(weight wise).  I am always looking through the local on-line ads & I am amazed at what some of the older model kilns have in them.  I would swear I have seen beefier elements in some of the old toaster ovens!  The Skutt PK kilns are all beefed up as that is what the P stands for, Production.  I am somewhat partial to L&L as they say the Hard Ceramic Element holders radiate the heat better into the kiln & cook the element less.  All I know is that they make it a breeze to change elements with no messy brick damage & using binding posts instead of crimping is an added bonus!  jhp