Test Kilns

[MikeFaul]

I'm looking at test kilns to test glazes, clays, and firing schedules. Our production kilns are Skutt 1231 PK Single Phase kilns... We fire to ^6, producing functional wares. What sort of features, volume, size, mobility (we are tight on space), element upgrades, would you suggest we consider? Also, it seems like we should stick with Skutt as the production kilns are of the same make (is this a valid assumption?) last our enviro vent system is maxed out with the two 1231's.

 

Is it wise to swap out the venting from the 1231 to the new test kiln or is this wrought with peril? Should we purchase a new venting system? Can we run a hose out the window, or do we need to run duct throughout the wall? One of my potters seems to think there no need to actively vent a test kiln, passive is fine, but this would vent into the primary workspace.

 

Your expertise and thoughts would be most helpful...

[neilestrick]

How big of a test kiln? Like just a little one cubic foot 120 volt model? On a kiln that size the brand quality is all about the same. They're just too small to have any real issues with brick longevity and such. On a kiln of that size you don't really need a vent. Many will need a 20 amp circuit, not the standard 15 amp 120 volt circuit. If you need larger than that, like an 18 inch kiln, then you start to see a difference in quality, and venting becomes necessary, and you'll go up to a 30 amp, 240 volt circuit.

 

The key to any test kiln is to get one with a digital controller so that you can slow down the cooling so it mimics the cooling rate of your larger kiln. Otherwise your tests won't look the same a when they're fired in the big kiln. I would stick with a kiln controller that uses the same type of controller as the Skutt, just because you're used to it, and it's the easiest one to use. The Skutt controller is based off the Bartlett V6-CF, as are the L&L and Olympic controllers. If you need info on L&L let me know.

[Guest JBaymore]

The key to any test kiln is to get one with a digital controller so that you can slow down the cooling so it mimics the cooling rate of your larger kiln. Otherwise your tests won't look the same a when they're fired in the big kiln.

 

 

What he said! 

 

best,

 

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

[MikeFaul]

How big of a test kiln? Like just a little one cubic foot 120 volt model? On a kiln that size the brand quality is all about the same. .

That was one of my questions. One cubic foot doesn't seem that big. We've seen glaze faults show on taller pots, but not on pots with a lower profile. So I'd like to test taller, shorter, wider in the same firing. I guess that means an 18" diameter on the interior, with about the same height. So, we could stack a platter or bowl over cups and mugs. That should also let us fire a gaggle of test tiles too...

[MikeFaul]

The key to any test kiln is to get one with a digital controller so that you can slow down the cooling so it mimics the cooling rate of your larger kiln. Otherwise your tests won't look the same a when they're fired in the big kiln.

So, we down fire now to 1500 before ending the program, I suppose all that would remain the same, but I would add an additional ramp to compensate for the faster cooling of the smaller kiln, correct? Is there a suggested ramp / temp at which I can let the smaller kiln cool naturally? Or, is this a trial and error thing based on total firing time in the larger kiln?

[neilestrick]

Typically you won't see any change in the glaze below 1500F degrees. Some people prefer to go as low as 1400F, but I've never seen that be necessary. I slow cool my two kilns, a 3.7 cubic foot model and a 21 cubic foot model, down to 1500F at a rate of 175F per hour, and there is no difference between the two even though there's a 12 hour difference in cooling from 1500F down.

 

An 18 inch kiln will hold a lot of small pots and a ton of test tiles. You can probably fit  25-30 mugs.

 

http://hotkilns.com/e18s-3

[Kohaku]

I've been very happy with my paragon Firefly- among other things, it has the computer controller discussed above...

[Guest JBaymore]

Mike, I see significant changes in some of my high fire glazes in the overglaze enamel firings I do to Orton cone 017 thru 014. So changes certainly can happen in that range too. Some of my glazes even change a bit at gold luster firings at 020 - 018.

 

best,

 

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

[neilestrick]

Mike, I see significant changes in some of my high fire glazes in the overglaze enamel firings I do to Orton cone 017 thru 014. So changes certainly can happen in that range too. Some of my glazes even change a bit at gold luster firings at 020 - 018.

 

best,

 

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

 

But those are both situations where you are re-firing at a lower temp, correct? Would those changes show up if you were to slow down the the far low end of the cooling of the initial firing, or are they specific to re-firing?

[Guest JBaymore]

They MIGHT happen more or less the same if the duration of the time (and the oxidation atmosphere) was similar on the cooling phase.  Let's say (arbitrarily) that something that is causing a visual change on the surface is happening during the time between 1300 and 1400 F.  If we look at my upand down time in that range.... and then include a slow cool in the same range of the same duration...... might very well be similar results.

 

But this is ceramics........ there MIGHT be some crazy reaction happening on the heating cycle .... but not on the cooling cycle.  Or the effect might be dependant on something that happened at 500 F.... and if it has not reached there yet (on a cooling cycle) ... it does not happen.  I can't think of the physics / chemistry reasons that it would off-hand.... but .... this is ceramics  .

 

best,

 

.......................john 

 

Edited to fix temps mentioned..... not 4000 F  .

[neilestrick]

Thanks, John. That's what I was thinking, too. I've seen all sorts of crazy things happen in re-fire, but I've never tried running the low end super slow to see if it would happen in the first firing. It seems like I see more of those changes happen in pots that were first fired in reduction. But that's just my observation, with no basis in actual fact or testing.

[MikeFaul]

Thanks, John. That's what I was thinking, too. I've seen all sorts of crazy things happen in re-fire, but I've never tried running the low end super slow to see if it would happen in the first firing. It seems like I see more of those changes happen in pots that were first fired in reduction. But that's just my observation, with no basis in actual fact or testing.

 

We just refired a mess of pots that had cratering in the glaze, it was suggest we refire two cones cooler, which we did. The cratering increased dramatically, some glaze ran off onto catch slabs, colors shifted to the ugly, and the pots were a sing'n and a ping'n... They all went into our plinking box. The last time we refired this way it worked fine, different glaze and clay, but it did work. We've been trying Standard 240G, which we found out has added Nepheline Syanite. According to Standard it makes some glazes melt earlier in the firing schedule. It would seem each glaze / clay combo requires a different schedule if we were to stick with the 240G, so we are now getting ready to test new white clay bodies...

[Guest JBaymore]

It would seem each glaze / clay combo requires a different schedule if we were to stick with the 240G, so we are now getting ready to test new white clay bodies...

 

One of the core concepts that I try to get across in my ceramic materials courses is that there is no such thing as a "cookbook" firing schedule. Firing profiles are developed to work with a specific set of clay bodies and glazes. In some cases... certain clay bodies and certain glazes simply cannot be fired in the same loads.

 

best,

 

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

[MikeFaul]

 

It would seem each glaze / clay combo requires a different schedule if we were to stick with the 240G, so we are now getting ready to test new white clay bodies...

 

One of the core concepts that I try to get across in my ceramic materials courses is that there is no such thing as a "cookbook" firing schedule. Firing profiles are developed to work with a specific set of clay bodies and glazes. In some cases... certain clay bodies and certain glazes simply cannot be fired in the same loads.

 

best,

 

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

So, part of testing would be to determine compatible combinations for a given schedule, and then work out production schedules accordingly? I'm starting to think we have too many combinations, perhaps we should take one, work out the schedule, once we have it stable, then move it to production. Then take the next combination using the baseline schedule as a starting point, tune it to the specific combination, then repeat until all four glaze / clay combinations are stable. For any given combination, coordinate wet clay, firinging, and glaze work to not mix combinations which require different schedules... This will take some time, we've set the next 12 months for testing, evaluating, and deploying all processes (production, maintenance, and business)... So, we have the time and budget to do it right.

 

This is more complex, much more complex, than I thought or knew a year ago... I'm living out your comments about the need for a baseline education and knowledge base to perform reliably, consistently, and safely... Oh well... I'm all in now... Thanks if someone were to try this my advice would be to triple their capitalization, education budget, timeline to deliver quality wares, and put a seriously experienced pro on retainer...

[Guest JBaymore]

Mike,

 

What you just wrote tells me that you are a wise man, and that you WILL succeeed in this endeavor.    Yup.... you got it.

 

Yeah...... ceramics is a pain in the butt.  On the good side.... you'll never get bored, and you'll always have more stuff to learn. 
"Clay is long........ life is short."  I've got about 100 lifetimes planned out for what I'm going to do with clay.

 

One of the reasons I built a noborigama is that I can fire each chamber differently, and get different results from the same set of clays/glazes ..... or I can fire different combinations that don't work well with each other in the same firing....IN the same firing.

 

best,

 

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

[neilestrick]

 

Thanks, John. That's what I was thinking, too. I've seen all sorts of crazy things happen in re-fire, but I've never tried running the low end super slow to see if it would happen in the first firing. It seems like I see more of those changes happen in pots that were first fired in reduction. But that's just my observation, with no basis in actual fact or testing.

 

We just refired a mess of pots that had cratering in the glaze, it was suggest we refire two cones cooler, which we did. The cratering increased dramatically, some glaze ran off onto catch slabs, colors shifted to the ugly, and the pots were a sing'n and a ping'n... They all went into our plinking box. The last time we refired this way it worked fine, different glaze and clay, but it did work. We've been trying Standard 240G, which we found out has added Nepheline Syanite. According to Standard it makes some glazes melt earlier in the firing schedule. It would seem each glaze / clay combo requires a different schedule if we were to stick with the 240G, so we are now getting ready to test new white clay bodies...

 

 

Mike, have you tried Standard 630? It's the cone 6 version of 182. No grog, but it has fireclay for a little tooth. I think it's much nicer to work with than 240.

[MikeFaul]

No... We have some 563 on order, I'll call Baltimore and see if they can't get some 630 on the same truck... It looks speckled, or is that just the fireclay? 

 

Thanks,

 

Mike

[MikeFaul]

Mike,

 

What you just wrote tells me that you are a wise man, and that you WILL succeeed in this endeavor.    Yup.... you got it.

 

Yeah...... ceramics is a pain in the butt.  On the good side.... you'll never get bored, and you'll always have more stuff to learn. 

"Clay is long........ life is short."  I've got about 100 lifetimes planned out for what I'm going to do with clay.

 

One of the reasons I built a noborigama is that I can fire each chamber differently, and get different results from the same set of clays/glazes ..... or I can fire different combinations that don't work well with each other in the same firing....IN the same firing.

 

best,

 

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

 

Frustrating, fun, weird, surprising, aggravating, enjoyable, peaceful, entertaining, fulfilling, expensive, but definitely not boring!

[neilestrick]

No... We have some 563 on order, I'll call Baltimore and see if they can't get some 630 on the same truck... It looks speckled, or is that just the fireclay? 

 

Thanks,

 

Mike

 

The 630 does not have speckles. Just a tiny bit of texture from the fireclay.

[MikeFaul]

200 lbs of 630 is on order! And, we ordered a test kiln too... A Skutt KM-181:  http://www.skutt.com/products/km-818.html We did not upgrade elements or brick thickness since we'll be down firing I didn't see the need for additional insulation for such a small chamber.

 

Cheers!

 

Mike