Safety question: Olympic gas kiln use

[mousey]

I got an Olympic propane gas kiln set up for reduction work and it's been an absolutely wild ride, but so far the one thing I havent been able to nail are proper reduced nitrate lusters.

Once thing I've been toying with; it has 3 burners coming up through the floor with a considerable amount of space around each, so I'm guessing that's contributing to why I cant replicate the classic sawdust / raku bath effects I'm looking for.  I would like to see if I can get there without the reduction bucket because the clay bodies I'm using generally cant deal with the thermal shock. 

Anyway I'm thinking about taking slices of thermal blanket and essentially stuffing it into those gaps around the burners.

My concern is that doing so will obviously impact the ability to feed oxygen to the fuel.. and that seems like a recipe for a catastrophic failure, potentially.

Anyone have any thoughts..?

[Mark C.]

Since what I call trash can gas kilns (like electric rounds) fire so uneven and are a bear to control I woulkd say try it nothing to lose.How are you trying to get nitrate lusters?? Is this fuming process at dull red on the cool down??

[Bill Kielb]

I am not familiar with reducing lusters, but pretty spiffy with respect to reduction. If I presume  you get great results in enclosed spaces such as Sagars, bowl interiors etc.... then your question is one of effective and even reduction in the kiln. Further your kiln and burners were designed with a primary air supply and secondary air is drawn in around the burners for several reasons.

Although everything I said there could be wrong and you are simply looking to get Raku style results out of your kiln. So maybe a little more about the desired effect, your equipment,  and your firing cycle. For most reduction, body reduction is super key for a number of reasons but you may simply want surface reduction.

Stuffing burners generally not a good idea though. so if you could elaborate further it may help me understand. Our recent Raku work found neatly  placing newspaper along the perimeter of the bucket and not necessarily stuffing it with sawdust yielded  predictable, excellent reduction without the texture of the sawdust and crude often thrown in. Some folks want texture and crud though.

[neilestrick]

You won't get Raku/sawdust effects by adjusting the burners. They are not the same process. You can put a mostly sealed saggar with combustibles inside your gas kiln, though.

Do not seal off your burners and try to fire the kiln. You'll damage the burners from the heat. Sealed burners typically have ceramic tips that act as a buffer between the heat of the kiln and the metal burner pipe.

[Mark C.]

ok melting burners is not good

[mousey]

So.. bit of background... fell in love with Beato's lusters early on and then discovered Greg Daly's book (and work) and decided to see what I could accomplish with a reduction bucket.  This is a porcelain body covered with what is essentially a very melty shino recipe with some nitrate salts added.  Fired to about ^06 then placed into the reduction chamber directly from the kiln, and Bobs your uncle.

And I'm super happy with how it came out, except that the body cracked.  As most of my porcelain pieces handled thusly do (and why shouldnt they; thermal shock, etc).

Sometimes I use a nice raku/sculptural body that is groggy enough to survive this sort of behavior but I have two significant complaints; 1) I love porcelain more and 2) the groggy clays tend to gather carbon on all the exposed, unglazed surfaces, especially the parts that directly touch the combustable medium.  Its an interesting enough look and sometimes even desirable but if you look at Greg Daly's work, its porcelain and clearly he obtains an appropriate level of reduction within his kiln to create the luster effect without actually inducing reduction through burning organics, eg paper, leaves, sawdust so on (aka what Beato used to do in her electric).  I've seen footage of him placing pieces in his kiln and later removing them that back up this assumption; they go into a firing chamber unfired and come out with lustered surfaces.

That, in essence, is my desired end game.

 

[Mark C.]

Could you fime the wares on the cool down-or reduce like I do every fire?

Maybe cover the grog body with porcealin slip for that look

[mousey]

Certainly viable suggestions, and thank you for them of course, but I think I'd like to understand conclusively why this isnt working as is..  so many possible variables.  Celadons come out great btw so perhaps reduction isnt the issue core issue?  I'd love to find out that this is simply a matter of technique and finesse and perhaps I'm blowing out the glazes and making the metals volatilize before the actual melt.. this is a possibility I suppose..

[liambesaw]

Have you tried mixing your own porcelain to make it more shock resistant?  I'm thinking of spodumene here, perhaps you could tinker with that aspect instead of the firing aspect?

[Bill Kielb]

I guess I would say I am not entirely convinced  the predominate effect is reduction?

[glazenerd]

Mousey:

search clay makers and find a porcelain body with pyrophyllte. Grog is a widely misunderstood additive. 

[mousey]

Just now, Bill Kielb said:

I guess I would,say I am not entirely convinced  the predominate effect is reduction?

Absolutely fair point but how is this any different than copper raku reduction effects, ultimately?  Daly's work with nitrate/copper lusters seems fairly well described but its certainly possible Im misunderstanding the physics/chemistry at the end of the day.

The porcelain mix suggestions are intriguing but way outside my comfort zone... that said I'll look for a vendor, definitely.

[Bill Kielb]

Interesting my understanding of reduction contains a mild background in chemistry so I really focus on copper, iron and tin mostly and to a lesser extent cobalt, nickel ......  my view of reduction is that of reducing the oxides which entails char, not necessarily  soot or carbon trapping.

............ might be reduction though. let me look at some Raku recipes and see how  and what they surface reduce. I am guessing copper but just a guess.

cool thing to work out, none  the less!

[Rae Reich]

Could you stuff the burner ports after/when you shut off the kiln? With kaowool? Introduce a bit of combustibles then?

[Bill Kielb]

Not very hermetic and what a mess!

[mousey]

I thought about somehow reaching down under the kiln and sealing them somehow with strips of thermal blanket but even with the gas shut off, I feel like there is zero chance I dont  bump into something and disfigure myself.  

[Bill Kielb]

Just a  few questions come to mind

Do you think that you are not achieving sufficient reduction with your current setup  and if yes and you do not have an oxygen probe during reduction do you have a positive jet from the lowest port plug? 

When you go  into reduction how do you achieve it with your kiln / burner setup?

What is your reduction schedule in general?

[mousey]

- It's tricky because I can do celadons fine so I know I'm reaching a measure of reduction.. but its nothing like the vacuum created when a reduction chamber's burning media sucks up all the oxygen.. and the disparity between the two is my primary culprit so far.  I've been measuring the jet from the upper most plug, not lowest, however.  I'll verify from lowest as well next firing (I have no oxygen probe).

- Notes from last firing, which was just testing out some new iron/copper/cobalt blends in an untested base ^6 glaze:

6:45pm start.  propane at about 15% throughput, flu open 90%, peeps in.

7:45pm 1033f

8:50pm 1140f propane bumped to 30% throughput.  flu/peeps untouched.  fast jump to 1500f.

10:30pm 2060f shut flu to 20% open, very strong reduction evident from top peep / flu.  Peep has a solid 5" jet when open.

11:26pm 2220f

12:40am 2260f shutdown.  ^6 witness cone is almost a puddle.

Again this is just me dicking around with a new glaze but it demonstrates how fast this thing goes from room temp to supernova, and it's certainly generating  enough reduction for celadons (attached).

I just got some ff3269 so I should be able to make some glazes that mature much more quickly.. I'll whip up another few tests using coppers as well as nitrates and put half in a reduction container and leave half in the kiln for reduction.  That should at least remove a few variables.   Updates to come.

[Bill Kielb]

I usually look for a jet from the lowest port just to make sure I have sufficient reduction at all levels. So the lowest peep is our safety check that the kiln is in effect reducing everywhere and we are not inadvertently oxidizing with secondary air.

The other thing I noticed is your schedule and our experience has been that our greatest reduction needs to take place between 1500 degrees and 1700 degrees. If we begin later, let’s say 1600 degrees, we find dead spots and low levels of reduction even though our oxygen probe says we are at about 0.8 or heavy reduction. 

For our typical schedule it is important to begin no higher than 1500 degrees else as things melt it becomes harder to reduce the oxides.

I also realize now that you have atmospheric burners and you are reducing your primary air by covering your flue which hopefully slows the primary air induction enough to get a sufficient rich mixture. This is typical for atmospheric burners but folks that tune these will by experience  generally pick a gas pressure, then flue covering, then fine tune their primary air shutter to a desired reduction level all while maintaining a desired firing speed. This way they actually have great control of the time they reduce which for our kilns needs to be about 1-1/2 hours  in heavy reduction between 1500 and 1700 degrees.

Going  super fast not always the greatest thing. Going the best speed and reduction level based on your own trials will probably allow you to dial different results in.

Just some food for thought though. I would be curious to see some celosia  red test tiles placed throughout just to gauge your current levels.

Just some more ideas actually, still thinking but there are also fire down reduction schedules to specifically get surface reduction.

I have a basic reduction video below that we ask our new reduction artists watch. Pretty basic but might be worth the view. It helps them formulate the basics and from there they build their own custom schedules. Prior to this their results  were super random, now they dial stuff in firing after firing.

 

 

[mousey]

So much to digest there, THANK YOU.  Honestly this kiln has no chill, getting a smooth sane ramp to 1500 is extremely difficult.  At least for me at this point in my evolution.  Also that digital control panel is mouth watering, and I'm 3 minutes into the video and already my core understanding of reduction is being redefined.

Also note that when I do the electric -> reduction chamber route, I take the pieces out at 1750'ish, max.  Higher than that and the nitrates seem to burn off.    I'll absolutely get some more experiments put together this weekend and ping back with results.  

[Bill Kielb]

Nice!

Sounds  like fun unraveling and learning!