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postalpotter

I'm a son of Sisyphus - firing a gas kiln, help needed

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 It's been awhile. I first joined the forum two years ago when I decided that I really did need a kiln. I had done some  firings in a small raku kiln I had built, how much harder would it be to build a full scale gas kiln? Well it is done. It has been a struggle. But I now have a kiln, I just need to learned how to use it.
The last time I was here I had plenty of help from Neil and Mark C and many others. I do appreciate all that they were able to do for me. 
 I just did my first glaze firing. I had done a bisque firing previously.
Before that I had never fired a gas kiln.
 My kiln is based on the Minnesota flat top it has a volume of 13.3 cubic feet with 2 low pressure Venturi burners I need to learn how to use.
  I'm using a type K thermocouple I take my temperatures opposite the flue. One 4in off the floor, the other 12in above that. The  thermocouple extends about an in. into the kiln. Until I get near ^3 my temps between those two points differ as much as 200deg. Within 50 degrees closer to ^3 I am going to try changing the bag walls setup and see if that will help balance the temp. How can I be sure I am hitting my hold temps. using a meter that shows temps that very so wildly? Do I suspect the meter? I was firing to ^5 when the temp neared 2030 I checked the cones. top shelf ^4 was melted ^5 was almost and  ^6 was kissing its feet. I will start checking sooner, another set of cones were on target and another close. Checking the meter the only way I could was with boiling water and a home instant read thermometer. Close enough. But is there anything else I could do to check the meter and have a bit of security?
 When I realized that I had over fired I shut down and closed every thing up. When I opened up, all my pieces had a million tiny bubbles. Guess I should have soaked a bit.

 How can I check my meter to see if I'm getting close to a proper temp. reading?

 Is there a firing schedule that someone could suggest I follow? I am using commercial glazes and at the moment I am using "potters choice" and Maco ^5 glaze.

 Also I've acquired an old Blue Diamond kiln with a sitter, I'd like to use to bisque fire. One of the element troughs is broken. I have the piece; I was wondering if I could use bisque fix to glue the piece back. 

 I really have no idea what I am doing here or I should say I know what I am doing here and that is asking for help!

 
 

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Sisyphus as in the Bill Dixon sense or as in the existential absurdity sense? Just curious. Welcome back. I have no help to offer-nothing useful to say except to confirm that you're in the right place! 

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9 hours ago, postalpotter said:

How can I check my meter to see if I'm getting close to a proper temp. reading?

 Is there a firing schedule that someone could suggest I follow? I am using commercial glazes and at the moment I am using "potters choice" and Maco ^5 glaze.

 Also I've acquired an old Blue Diamond kiln with a sitter, I'd like to use to bisque fire. One o

Ok, first download a K type thermo couple chart and you can check it’s output with a meter. Thermocouples are simple devices, two dissimilar metals welded together so their accuracy is amazing from one to another for such a simple device. Actually pretty goof proof.. so unless your pyrometer is off, your readingS are probably just fine. This brings us to a second possibility in that cones are about  time at temperature, the pyrometer is just a temperature at a point in time.

Understanding a bit about cones will also help, If you look at a cone chart there will be firing rates  for the last 200 degrees of the firing. The center column for instance says that going 108 degrees per hour for the last 200 degrees will get your cone 5 cone to bend at 2167 on your pyrometer. So that is a better way to understand the relationship of cones and using a pyrometer to approximate a cone bend. This works because the most relevant heatwork done, is in the last 200 degrees of the firing.

firing slower often evens things out a bit, so next suggestion and maybe the first thing to try is a slow glaze firing just to determine if your kiln fires even enough at a slower rate. You can find a popular often used schedule in the genesis manual by Bartlett controls. These are the automatic controls you see on nearly every kiln model in the US. Their manual is on their website free to download and has several Glaze schedules you can try.. the medium speed cone fire schedule has been used tens of thousands of  times if not more.

There is a lot to learn, but often working through these issues is a good way to learn so hang in there. Pictures of your finished kiln, bagwall etc... might help spark some additional observations here.

Oh yeah, As far as bubbles, often soaking makes things worse, so I am not convinced that you need to soak more.

Edited by Bill Kielb

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9 hours ago, Bill Kielb said:

Oh yeah, As far as bubbles, often soaking makes things worse, so I am not convinced that you need to soak more.

in what way? Have always had a 20 minute hold and never had an issue and when we started doing it it really helped across the board on glaze issues. 

Hey OP you said you did a bisque firing a while back, did you clean up the pots before you glazed them ?

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Just curious if you by soak you all mean drop and soak - reduce temperature from peak, hold temp before free fall/cool - e.g. I've been dropping about 100F from peak, then holding there before shut down.

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Ya know I may have spoken out of turn as I fire cone 6 electric electric (cone 5 with 20 minute hold) not gas but I do have a 20 minute hold at top temp although I did program those firing schedule 10 years ago so maybe it drops before the hold, to be honest I just reuse the schedule and haven't paid attention to it in years other than to make sure the schedule is complete and drop starts. Early on we were having various glaze issues just firing to cone 6. Did a lot of reserach at the time and played around with various hold times and landed on 20 minutes with our glazes and pretty much all our glaze issues went away. I assumed gas would act the same way but maybe I am wrong so prob should have stayed out of the thread. I was just curious what Bill was to referring to that was made worse by soaking.

We also had a pitting problem early on and cleaning the bisque ware well just before glazing cleaned that up so it was the reason we were having that problem. I get other things cause it as well.

If this is a gas thing and not the same as what I do in electric then sorry for jumping in and confusing the thread.  

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Aye. 

I misspoke as well - had tried drop from peak and soak, then aimed for a lower peak, with about the same drop and soak, now lower yet, with a short hold at peak, then drop and soak - iow, getting about the same heat work, with lower peak temp, then a hold ~100F below peak.

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14 hours ago, LeeU said:

Sisyphus as in the Bill Dixon sense or as in the existential absurdity sense? Just curious. Welcome back. I have no help to offer-nothing useful to say except to confirm that you're in the right place! 

I think he means the literary sense, it usually means someone does things the most needlessly complicated and frustrating way possible.   I take it as a self-deprecating joke in this context :lol:

 

Either that or it means his horses ate him alive during a chariot race.

Edited by liambesaw

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@postalpotter Ignore the pyrometer when it comes to accuracy. Cones are the only way to know for sure what's going on, especially in a gas kiln. Just use the pyrometer to give you a basic idea of rate of climb and a rough estimate of temperature. Once you've got the cones dropping together at the top and bottom of the kiln, you can see if your thermocouples are off and calibrate them as needed. If you're firing to cone 6, use cones 08, 04, 2, 4, 6, & 7. That way you can see how even things are as the firing progresses and see if your thermocouples are showing similar results.

Bubbles may or may not be fixed by soaking. It all depends on what's wrong with the glaze. If it's bubbled because it's over-fluxed then soaking won't help at all. But in other cases it will. It's worth a try. Just remember that soaking at peak temp adds heat work and increases melt so runny glazes will run more.

Don't try to glue the broken electric kiln brick back into place. It won't work. If the piece is big enough just pin it in place with element pins. If not, put some pins in the brick to hold the element so it can't flop out. Replace that brick next time you replace the elements. Blue Diamond Kilns went out of business a few years ago, but Euclids can make elements for you.

 

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21 hours ago, Stephen said:

in what way? Have always had a 20 minute hold and never had an issue and when we started doing it it really helped across the board on glaze issues. 

Drop and hold is one of the ways to get your glazes to heal. Firing  one cone less with a 15 -20 minute hold still drops at the cone desired but keeps the peak temp from occurring so can be sort of an attempt to get the glazes to heal or you just like the melt that way, or the recipe is very temperature dependent and does not tolerate any overfiring.   Not  quite as dramatic as the drop and hold but similar idea going on there. A bit about the surface tension of the glaze at a specific temperature. Anyway, intuition would say get it hot and keep it there theorizing It will melt and fill in, but often dropping temp a cone or two and  holding  is more successful at getting that done. Holding at peak temperature often exacerbates some of these problems and when it does, the solution is frustrating because it’s counterintuitive.

Edited by Bill Kielb

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21 hours ago, postalpotter said:
 
 ...My kiln is based on the Minnesota flat top it has a volume of 13.3 cubic feet with 2 low pressure Venturi burners I need to learn how to use....

I'd love to see your kiln.  Do you have any pics you could share?

 

Jed

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Hey all,

 Thanks for the input. I look forward to getting to know you all. BUT now right now 10hr days handling the US Mail has taken the life out of me. I will read and do my best to comprehend what ya'll have shared. Pictures to come! Oh the bisque fire was a bust! 

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On 6/30/2020 at 10:00 PM, LeeU said:

Sisyphus as in the Bill Dixon sense or as in the existential absurdity sense? Just curious. Welcome back. I have no help to offer-nothing useful to say except to confirm that you're in the right place! 

 Just think of the glazing progress I would have made if I had just gone electric. I have made ONE glaze firing in two years.  My kiln was originally almost 17cubic ft. but it was to much for my burners to do in 14 to 16 hrs. so I rebuilt top and shrunk the kiln. I still work a full time job so when I had the chance to do a bisque firing I opened the kiln to load and realized that the flat top  was sagging! So I rebuilt the top again! Read some of the older post to find out that I have built and rebuilt this kiln 5 times and I have only fired with pieces in it twice and the bisque fire did not go so very well. Bed time! 

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Fire with cones pyrometers are just a guide as Neil says-Where you doing reduction firing-if so maybe to much reduction which can cause bubbles .How long was the fire in hours?Cone 6 gas firing you say?I recall your space age kiln.

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On 7/2/2020 at 9:49 PM, Mark C. said:

I recall your space age kiln.

 LOL ya! you saved me a hell of a lot of heartache when you caught   on to the fact that I had bought the wrong hard brick.

  I  had a bit of a problem with the burners.  Ward had set me up with one regulator feeding both burners from two tanks, the regulator couldn't  deliver the proper pressure to both burners. That was part of my problem with my failed bisque attempt. I would produce an inefficient flame.  I finally figured it out while I was doing the glaze firing. I got another regulator, split the tanks and watched the flame even out.  Before that I would have problems producing carbon, kept finding it on the tip of the thermocouple. I was not trying to do a reduction just a successful firing.

 I was firing to ^5 and shut the kiln down at 12hrs.

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On 7/1/2020 at 1:05 PM, neilestrick said:

Blue Diamond Kilns went out of business a few years ago, but Euclids can make elements for you.

Yea, they where about a mile from were I grew up, to bad I wasn't into this before they shut their doors.

 Say Neil I need to be able to candle, the kiln is outside with a metal shed cover I live in NOLA where humidity is tropical! I need to have a small burner to candle with, I can build a simple venture black pipe burner. My burners have a basso, if the kiln is still well vented could I pass on the basso for the candle burner? It would be a piece of pipe about 24"long with about 22 slits for a small blue flame? I do not want to have to sit an watch the kiln for the 8 to 12 hrs. while the kiln heats. Any best ways to dry out the kiln and the soft brick?

Edited by postalpotter
spelling

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On 7/1/2020 at 12:04 AM, Bill Kielb said:

Understanding a bit about cones will also help, If you look at a cone chart there will be firing rates  for the last 200 degrees of the firing. The center column for instance says that going 108 degrees per hour for the last 200 degrees will get your cone 5 cone to bend at 2167 on your pyrometer. So that is a better way to understand the relationship of cones and using a pyrometer to approximate a cone bend. This works because the most relevant heatwork done, is in the last 200 degrees of the firing.

firing slower often evens things out a bit, so next suggestion and maybe the first thing to try is a slow glaze firing just to determine if your kiln fires even enough at a slower rate. You can find a popular often used schedule in the genesis manual by Bartlett controls. These are the automatic controls you see on nearly every kiln model in the US. Their manual is on their website free to download and has several Glaze schedules you can try.. the medium speed cone fire schedule has been used tens of thousands of  times if not more.

Just what I was looking for! Thanks for the directions to it.

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2 hours ago, Mark C. said:

Yopu only need a pilot until kiln reaches red heat really  then the gas will ignite on its own

 I am guessing you are referring to my question for Neil and my need  to preheat the kiln? I have a problem getting a clean flame when I am trying to get the kiln warmed. With humidly at near 90%  and up for 362 days a year the soft brick will hold some moisture.. My low pressure burners produce a yellow flame with anything under 3# pressure and heat to fast above that. I was thinking of something like a bbq pipe burner?   

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I wouldn't worry about that flame. Nothing is sealed Before you get to an "oxidizing" flame. So it shouldn't matter.

I was worried, until I tested stuff, broke stuff, and haven't found problems.

I'm single firing, so I am very concerned with a slow beginning, clean burnout etc.

My orifice is drilled solder, so I don't like letting the flame get down to it. JAS is just above sputter. Keep it at JAS and you should be alright.

Sorce

 

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I would not sweat the low dirty flame either-it will all be fine even if it soots up for an hour or two on low while the bricks are drying out.

My burners on natural gas put out soot at super low level-it just burns off later with no bad affects.

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22 hours ago, postalpotter said:

Yea, they where about a mile from were I grew up, to bad I wasn't into this before they shut their doors.

 Say Neil I need to be able to candle, the kiln is outside with a metal shed cover I live in NOLA where humidity is tropical! I need to have a small burner to candle with, I can build a simple venture black pipe burner. My burners have a basso, if the kiln is still well vented could I pass on the basso for the candle burner? It would be a piece of pipe about 24"long with about 22 slits for a small blue flame? I do not want to have to sit an watch the kiln for the 8 to 12 hrs. while the kiln heats. Any best ways to dry out the kiln and the soft brick?

For safety, your burners need to have a pilot burner with a flame sensor and shutoff valve. A Baso valve is the simplest way to do that.  The pilot burner could be a very small burner LIKE THIS  that primarily just keeps the main burner lit but can get the kiln up to 200F overnight, or you could use a small venturi burner that puts out more heat. With power burners you generally only need two, so you just put a Baso valve and burner on each one. If you've got multiple venturi burners (some larger kilns have 6-10 burners) it can get expensive and complicated to put a valve and pilot on each burner, so they use a pipe with little holes (ring burner) that goes to all the burners, and a flame sensor at one end. I don't love those because if holes get clogged you could have a burner that doesn't have a pilot flame on it, but it seems to be the standard for that type of setup. I would just be careful to check the pilot flame at the start of each firing.

If it's just humidity, I wouldn't worry too much about moisture in the bricks. It's not like they're getting rained on and soaked, and soft brick won't blow up since they're so porous.

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On 7/5/2020 at 8:16 PM, Sorcery said:

I was worried, until I tested stuff, broke stuff, and haven't found problems.

 

On 7/6/2020 at 10:31 AM, Mark C. said:

I would not sweat the low dirty flame

 

On 7/6/2020 at 12:12 PM, neilestrick said:

For safety

 

On 7/6/2020 at 12:12 PM, neilestrick said:

soft brick won't blow up since they're so porous.

Thanks to all!

Sorcery, thanks for breaking things so I don't have to! I really don't produce enough to not make that a painful exercise! 

Mark,  thanks again for helping to soothe my fears and arming me to fight off the gremlins.

Neil, always safety first.  Some of the neighbors are pretty sure I may blow-up the block!

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