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Kristin_Gail

Real-Time Kiln Advice (Kiln Curently Firing)

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So. I'm finally firing my kiln again (see last firing's questions here: http://community.ceramicartsdaily.org/topic/5746-troubleshooting-this-converted-kiln-o-mine-taller-chimney/).

 

This time, I adjusted the regulator to fully open; built the bagwall up to 13.5" high (with spacing in wall), from a previous 4.5" high; and put a 36" metal extension on the chimney.

 

The burners are far, far happier - they're burning blue instead of orange.

 

But I still have to fire with the damper almost completely closed if I want the temp to rise at all. It's a 9 x 9 hole, and there's only a 1 x 9 section open right now. Anything more than that, and the temp drops rapidly.

 

I'm re-firing all the pieces from last time, so figured I could go faster than usual. Averaging about 250/hr or so. I slowly raised the gauges (measured in water columns) every so often - every 2-3 hours.

 

I'm at hour 7 of the firing, and the dials on the burners are almost maxed out (4.5 of 5.8). Temp is just below 1600°F. Rising okay for now - about 200°/hr.

 

I'm concerned that, in a few minutes, I will again - for the third time - fail at reduction. With the damper closed down so tightly, there isn't much wiggle room between neutral and smoke. I have such a difficult time finding that "4" flame from the spy holes" spot.

 

In addition, with the dials being so close to fully open, I will again be stalling at 1900° (for the third time).

 

Honestly. What in thee heck am I doing wrong?

 

John B. mentioned that a novice error is to turn up burners when really what you need to do is turn them down. I've tried this. I've tried moving the damper to all sorts of positions, gauges up and down, etc. The only thing that makes temp rise is closing the damper way down and, oddly, taking OUT the kiln shelf I have covering the gap above the damper. (Does this make sense? The damper is thinner than the damper slot, so someone here told me to cover the 3/4" high gap with something. When I cover it, the temp drops.)

 

Geesh. Getting close to reduction temp now ...

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I am thinking that your secondary air is way too much. This is the dial on the back of your burners. Crank it way in to about 1/4 inch, or the thickness of a pencil.

You also mention a brick covering up your kiln shelf damper. If you remove it, more cold air comes in above the kilnshelf, into the chimney. This is called a passive damper. This will slow your draft down.

Good luck.

Tom.

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I am thinking that your secondary air is way too much. This is the dial on the back of your burners. Crank it way in to about 1/4 inch, or the thickness of a pencil.

 

That shutter is primary air... not secondary.

 

So that is three changes all happening simultaneously for a test.  Too many variables changed for one test to read what is what.

 

I'd need video for a lot of the aspects of the kiln to say more very effectively.

 

The "blue" on the burners sounds like a good sign.  At least they are able to entrain some primary air.  That gives you some control.

 

The about 1" open (are you sure about that) on the damper sounds potentially plausible now that you have some primary air available.  You will find that changes of 1/8" on a kliln that size will make a differencde in the atmosphere and climb rate.

 

FYI...... Letting air into the chimney has the same effect on the kiln draft as closing the damper.

 

Make a change and wait at least 10-15 minutes to evaluate what it is doing.  Don't be changing things every 5 minutes.

 

best,

 

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

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Pottery instructor at the local craft college just happened to call me at the very moment I was attempting to reduce. He, too, suggested closing down the primary air - all the way. With this change, and playing with the damper, I still can't get a little flame coming out the spy hole. I get nothing or the burner flame coming back out the burner ports. I ended up leaving the primary air closed and the damper open just past that bad "flames shooting out the burner ports" point, getting me through 1800F in what I hope was reduction.

 

I'm now open slightly past that on the damper (back to 1" x 9" opening) and opened the primary air to about 1/3 open - yes, about the width of a pencil.

 

Brian, I'm firing on two completely full-up 100-lb propane tanks. It's about 65 or 70 degrees out today. Quite windy, too. I seem to use about 1/4 of the tanks or so on each firing, so they're probably 90% full right now.

 

I do think a lot of this has to do with the primary air. It's just crazy to me that I have to damper it down so much still - it makes me think my chimney is too big, not too short.

 

Slowly approaching 1900F now. Will it stall there again? I will keep playing with the various dials and levers.

 

And yes, John, I will try my best to wait after making changes. It's tough, though, when I cover up that passive damper and the temp falls by degrees per second. I can't watch that for more than a minute or so - it's painful! I keep giving it a try with the hole covered, but I simply have to have it open in order to not fall rapidly. So there it is for now.

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Thank you so much for your quick help, everyone. I know it takes many firings to understand a particular kiln, and that number will be higher as I am so inexperienced. But it's certainly frustrating when it's the same issue each time - and I'm convinced it's something silly I'm doing. So envious of all of you who've had proper training.

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I would say damper down more when trying to reduce and add some primary air a little at a time to build pressure to get a fame out the peepholes. You do not want back pressure of the burner tips. I am wondering why you made the bag wall 36 inches tall. Is that what you meant? 

Marcia

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There really was a marked difference in the kind of flame when we adjusted the regulator. This makes me happy! It was a messy, floppy, orange flame in previous firings - a flame that threatened back-burning. Now it really is much happier. Blue and making a nice sound.

 

I'm going to take a look inside to see where the flame is headed.

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With the previous tiny bagwall, the loud, bright, FAST flame would come in, jump over the wall, and go right out the flue - under all the shelves. I watched it happen.

 

But today it's coming in loud and fast, hitting the wall, obviously bouncing up high. Then it goes out of my view. The next time I can see it is 2/3 way through the kiln, and it's a very, very, very slow, licking flame. It appears to only be touching one of the shelves full of pots before it turns and makes its way out the flue, under the other shelves. But this slow, lounging, licking flame - this is what I'm looking for, no?

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Without visuals... very hard to say.

 

With those two burners, if they were operating correctly and the damper was adjusted correcly and the air balance was set right, you SHOULD be able to get that small kiln chamber completely full of products of combustion and actually have the flame-front burning off in the base of the chimney (reduction conditions).  In that case the chamber would apperar "hazy" and while you could see some quality of flame within the chamber... that might look like silk gauze rolling in a breeze...... you wouldn't typically see a separate flame and totally clear atmosphere elsewhere.

 

Have you ever been involved in reduction gas firing elsewhere?  If so... how does what you are seeing compare?

 

Video clips would help.

 

WIsh I could be there......... sorry.

 

best,

 

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

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Oh, my. Don't apologize. I can't believe how much help everyone has been able to give me, and how much of it has actually worked!

 

It reached Cone 4, slowly, and I began spraying soda. Almost done with that task, then I'll just keep playing with the damper and primary air, I guess, as the gauges are turned up as high as they will go. I know the kiln isn't meant for wood, but it looks like I might end up using some again, just to get to Cone 6.

 

That call from the ceramics instructor - it's about his class coming here (ha!) for a field trip next week. They're visiting a string of potters - I think mine is an example of, "Look what can happen to you if you don't graduate from this program." In any event, I'll do my best to convince him to come back to help with the next firing. Perhaps he can even find some answers when he takes a look at it, not firing. I can only dream.

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It worked! Holy crap, it worked!

 

It was realllly slow at the end - I can't imagine it could have gotten any hotter than what it did (2190 or so - Cone 6 was tough to see, but pretty sure it fell). And there's no way it would have worked in colder conditions. And I couldn't figure out how to get it *not* to reduce from Cone 4 to finish. (I opened the primary air in increments, ended up all the way open; adjusting the damper either caused reduction or, a smidgen more open, caused temp to fall.)

 

But hey, it worked! No wood used! And for once I didn't jam the silly garden sprayer.

 

Phew.

 

Have I mentioned I'm thankful for so much help? I am. I am, I am.

 

I'd still really like to know why I have to fire this thing with the damper almost completely closed - I think, Marcia, you once thought I should be firing it with it half open or so?

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I always fired with the damper 1/4 open on kilns  I have built and dampened down for reduction. Rarely needed to open it more. I could get licking flame out of the bottom peep and a harder flame on the top in the kilns 40-60 cu ft.. I am sure you need to find the balance between your burners, draft, barometric conditions, stacked conditions, etc. in Montana I preferred low barometric pressure...it depends on many things. You are using a retro kiln situation so you have to figure it out. I am glad you hit temperature.

Now we will wait to see your results. Congratulations.

 

Marcia

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Ha! Neil, I live in New Brunswick, Canuckia, about three hours east of the Maine borner. There are numerous potters within a two-hour drive of me, some of whom have even been nice to me and might be convinced to visit. However, near as I can tell, 90% of them fire electric, the other 10% wood. I have a feeling a lot of my questions will be answered when the field trip arrives next week. The instructor leading the trip is very kind, with gobs and gobs of experience. He's already been key to this thing working at all.

 

You should (and will) see the results! Out to take photos.

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This firing was relatively even in temp.  A range of Cone 5 starting to bend to Cone 6 almost done.  So, so, so much better than before.

 

But what I saw when I looked into the kiln while it was hot - the hard, fast flame going up from the bag wall, then further down the kiln the soft, licking flame only going in one spot - that's absolutely evident in the look of the pots.

 

Here's what I saw (not really to scale):

 

01.jpg

 

The bag wall is the same height as the second shelf - but the flame just snuck under it.  You might be able to see it from this photo:

 

02.jpg

 

All the shelves (B,C,D,F) but one (A) turned out white pots with hints of soda and light hints of flashing.  Like this:

 

04.jpg

 

I had some pots in there with Malcolm's shino, and every one of them came out stark white.

 

But the one shelf, A, that the flame touched, was dark, dark, and full of soda, colour.

 

08.jpg

 

The two larger mugs had nothing on them; the smaller, redder things had a slip.

The cones on this shelf were grey instead of white.  I can't find a reference but am guessing this has to do with amount of reduction?

 

I like dark.  I love the dark.  Am looking forward to learning, playing, tweaking more, in an effort to get all dark.

Mark McCombs likes this

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The pieces look great! Congratulations. 

A few well intended comments:

You could use a couple of target bricks in front of your burners to avoid turbulence when it hits the bag wall straight on. They would  bounce the flame up over the bag wall. You can see a black mark on the bricks in the bag wall where the flame hit it directly.

The shelves look a little sparse too. Maybe pack denser next time you don't need that much space for the salt or soda to get around the pots.It actually helps with the firing making it more even and easier to control and reduce.. I would reverse the stacking with the taller and three shelves in the front and a little less dense than the front in the top back. Was shelf E empty? Try loading like you're building a maze for the flame. Were the two nice mugs on the bottom front near the flame or in the back?

 

Good job with the firing.

 

Marcia

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Definitely use target bricks. It will help with a lot of issues. If the reduction was uneven, it should fix itself once you get good pressure in the kiln. If you've got pressure out top and bottom spy holes, then you're more likely to have even distribution of the reduction. Did you do an actual body reduction period around cone 08, where you put it into reduction and stall out the temperature for about 45 minutes?

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Hey, guys.  I'm looking at another firing of this kiln tomorrow, and am attempting to review and implement your advice.  My guess is I'll be back here tomorrow ...

 

Marcia, the kiln was horribly loaded last time, very very loose and even empty the top 10" or so.  I've done much better this time.  Not perfect - It's very tight all the way to about 4" from the top, then loose (as I ran out of pots of that height or shorter).

 

Neil, I was using the pyrometer instead of cones to judge when to reduce - shooting for reduction from 1623°F - 1850°F.  (Using cones for the end of the firing, though, of course.)

 

The fellow who visited with his ceramic students - he suggested I make the bag wall even taller, and tighter.  Also, when I mentioned target brick, he suggested using a tall piece of kiln shelf, spanning the width of the kiln, propped up at an angle against the bag wall, to deflect the flame.  I did this with three different pieces of kiln shelf, overlapping each other.  I should probably take a photo ... 

 

bag_wall_target.jpg

 

Are you guys rolling your eyes at this, or have I possibly done something to help?  I hope.

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For me I would put in those target bricks and tighnen the bag wall just a bit .That load looks way to loose I would also do as Marcia suggested put the tall stuff in the back-the flame will just pass thru that open tall stuff as you saw. You want it to get restricted by the load and be forced thru it.

How about a postitive brick stop under the middle of floor so flames have to go to the rear to get out.Thats betwwen a& b shelve underneath them?

Pack the load tighter next fire-think like a flame and force it to flow where you want it to go.

Take a look at that salt load I stacked in Molokai workshop thread under education-this was a 1st time fire and it worked as good as it can get.

I packed that load as tight as I could with student works which tend to be all over the board in sizes.

It looks like you got some keepers-maybe more reduction as well next fire.

Mark

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Mark, you're saying it was too loose in the pictures on Page 1, the other firing, right? Or do you mean the photo I just posted is still too loose?  Besides the top shelf, 4-5" from the top (which those tester things are on), the rest of the kiln is pretty darn close.  A couple open spots on top of large plates, etc., but otherwise 1/4" or so between most pots.  (I just realized it's closer to 1/2" between pots right there at the front of that shelf, except for that bottle on its side. So now I think you're talking about this photo.  Damn it, I thought it was tight.  I guess it isn't.)

 

I'm having a difficult time finding the photos of the salt kiln you mentioned.  Can you help me find the thread?

 

I love the idea of a brick between the bottom two shelves.  Completely logical.  I'll have to try it next time, though.  Just spent all day loading this thing - would take an awful lot to get me to unload and re-load it.

 

I can, however, still tighten up the bag wall more - and am very open to switching the big shelf deflectors to some sort of target brick.

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My comments where not on your most recent photo

but now that I have seen that I would add the target brick as it breaks up the flame -the shelves just push it up where as the target brick splits the flame into many.Just put a brick on end in front of flame path where your shelves are-I would take them out-myself as your flame dis go up last fire you said.

The bag wall on right side has a larger gap  on a few bricks-I would even that out-you could add a few more loose bricks to that bag wall if you want it to go higher?maybe a soap  brick or two?

Mark

 

heres that salt fire a few weeks ago

http://community.ceramicartsdaily.org/topic/6027-molokai-workshops-at-molokai-arts-center-this-month/?do=findComment&comment=58763

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