How To Fire A Fibre-lined Gas Kiln

I’ve posted in the past about how I fire my gas kiln.  There are actually alot of posts – just “search” on my website for “gas kilns” and all the previous posts will be listed or just Click Here.

I’ve fired my kilns a lot lately and have had a few questions, so thought I’d do an update on how to fire a fibre-lined gas kiln.

I’d always dreamed of having my own gas kiln.  In the states, it’s pretty improbable- very expensive – got to have a site, etc.  So when I landed in a great space in Australia and the opportunity to do clay full-time, I started looking for a used gas kiln.

Fortunately, old fibre-lined gas kilns are fairly available in Australia.  I ended up buying 2 – one for $2000 (the lady was going into assisted living and literally “gave” me her studio – wheel, tools, chemicals, clay and the kiln) and the second one for $150.00.  I was extremely lucky.

Both kilns are great!  A little worse for wear, but still highly usable.  The older black one is named Thelma, and the shinier, newer one is named Louise.  They are two hot bitches that like to go fast!

Fortunately for me, they’ve allowed me to figure out their idiosyncracies and let me fire them well.

When I got these kilns, I sought advice, talked to people, looked on the internet and hoped for a step-by-step instruction manual on how to fire a gas kiln.  None existed and everyone said, “Each kiln fires differently.  There are no exact instructions.”

Well that is just hunky dorky…… Here’s a post on my first firing:  Click Here.

So, I set about firing it, trying, learning, continued to ask lots of questions and fired it some more.  When I say “it”, I’m referring to Thelma as I didn’t even fire Louise for at least a year.

As a result of my experience, I thought it might be helpful to some that are trying to learn to fire a gas kiln if I passed along some information about the process.

Here are some insights (in no particular order):

Propane Tanks-I keep two large propane tanks ready for firing.  As one is depleted, I have it filled, but try to start out on the “almost empty” tank to drain it down as much as possible.  Funny, I can almost get to 1000c on the dregs of an almost “empty” tank.  If you have two tanks, then if a tank freezes (ices) up, then you can easily switch tanks and keep firing.

Meter at the tank-I generally start firing at 35kpa on the meter.  For reduction on Thelma, I have to up that to 100kpa to get her into heavy reduction (more on reduction later).

Burners – my kilns each have two burners.  I light one burner in the beginning of the firing with a propane lighter.  I keep the door to the kiln open until I’ve lit the kiln, then I close it.  I light the second burner at 600c.  In order to “see” the burners on Thelma, it is necessary to place a mirror under the kiln -thus allowing full view of burners without having to lay on the floor (uncomfortable!).

Pyrometers – I use a digital pyrometer in each kiln to ensure that I can track the temperature.

Cones – I place a cone pack of 3/4 relevant cones in front of each bung hole and one on the lowest shelf to make sure I’m firing evenly.  I make a bunch of cone packs, using cones 8,9, 10, way ahead of time to make sure they don’t explode in the firing.

Bungs – my kilns came with fire brick cones, but they have broken over time.  So now I use use a rolled up piece of fibre – works great!  I put bungs in at 600c.

Reduction – It’s easy.  For copper reds, start redux at 750c and keep it in redux til the end of the firing.  To put your kiln in redux, you may need to up the gas output at the tank to 70-100kpa (I do).  Then I screw down the burner leaving only about 1/4 inch opening on each burner.  I also put fire bricks on each flu closing it to 1/2. Watch closely and if you see any black smoke, open up the burners or the flu til the smoke stops.  Black smoke is bad – indicates that carbon coring can occur – very bad for your pots!  Check to make sure that your kiln is in redux by pulling out the lower bung and seeing if a flame is coming out of the bung – you want a 3-4 inch flame.  You probably won’t see flames out of the top of the kiln (out of the flu) until you’ve passed 1000c.  Reduction can slow the kiln down, you have to babysit it sometimes.  If it stalls, I try everything and still keep it in redux – open the flu a bit, open the burners a bit, change the gas at the tank, check if the tank is frozen (if it is, you can hose it down with water to unfreeze it).

Oxidation – It’s really easy.  Fire the kiln until it reaches the desired temperature and the cones have dropped.  My problem is keeping the kiln out of reduction.  To do this, I have to slow down the tanks, the gas coming in and the burners.  But hopefully, this won’t be a problem for you.  Here is what a glaze that should be fired in oxidation looks like if it reduces – interesting, but no terribly pretty.

Closing up your kiln – When your kiln reaches temperature (this will vary for each kiln.  One of mine reaches cone 10 at 1240. The other one goes to 1260 to reach cone 10), turn the gas off at the tanks.  Then close off the burners with fiber or the doors for each burner port.  Put a brick over the flu outlet to completely cover it.

That’s it!  Go home and go to bed.

Be patient!  Don’t open the kiln too early.  I may “crack” the door at 200c, but you’re risking cracks if you unload too early.

Hope this has proved helpful in some way.  Let me know if you have any questions!

Good firing to you all!

Marian