Basics of Firing a Salt Kiln

Firing any fossil fuel kiln can be broken down in a few different ways.  We will organize it as startup, ramping/atmosphere control and firing off- roughly beginning, middle and end.

Starting a kiln: lighting burners-

Before lighting any kiln make sure all the burner valves are off.  We have a separate main valve gate so this is especially important when we first open the main.  The burners (natural gas in our case) are nothing more than carburators.  They mix air with gas. Our burners are homemade "alfred" type, using basic pipe fittings.   I will post images soon.  You can find the design in books on kiln construction. They have a small chamber containing an orifice for the gas and a primary air port, or gate,  to let air in to mix with the fuel. We also have used manufactured venturi type burners which operate in the same way.  They are easy to find and operate.

To light the burner, use a small propane bunsen torch as a pilot. (Use the appropriate safety gear.  I will assume this through out these posts.  There is plenty of information about safety in books and magazines.)  Make sure the primary air is closed tightly.  Light the torch and place its flame in front of burner you are going to light. Slowly open the burner gas valve until a small amount of gas is released.  We call this cracking the burner.  When the burner ignites the flame should be lazy and yellow.  Leave the flame this way for around ten minutes or so. This will warm the burner, making it safer to introduce air to the flame.

After ten minutes, usually less in the summer, the burner can be adjusted. Give it more air to get a hotter, cleaner flame.  This is done by slowly opening the primary air port.  Give the burner enough air to turn the flame blue.  You may see some yellow at the tip.  This is fine.  You want an "oxidizing" flame.  This is a clean burning flame that has sufficient air to burn all or most of the gas.  Do not give the flame too much air.  This will result in the flame being cooled by it own air supply.  It can also result in "coughing" or back burn where the flame recedes into the burner chamber.  You will hear it.  The burner will also get very hot so be careful. Shut the burner down for a minute and start over.  Repeat this process until all the burners are on. The timing for lighting burners depends on the pots in the kiln.  If you are firing greenware the kiln should be fired slowly.  We fire bisque, so lighting all the burners (4) can be done in a shorter time.

Please note that I refer to sensory cues. You will not learn to fire a kiln (or troubleshoot) by being given numbers, or inches, or the like. I will give some quantitative reads at times for sure.  But all kilns (and burners) are different so a good general knowledge the process is key.

Once all the burners are going with a nice lazy blue flame, you can relax for a bit, have a bite or a cup of coffee before ramping the kiln.

Our firing schedule is roughly this-

8:00 or 9:00 am- start the first burner.
By 9:00 or 10:00 am- all burners on.  Start ramping.
Ramp kiln to ∆ 010 - ∆ 08 (1650˚f -1750˚f, roughly). Start reduction*
Ramp and reduce until ∆ 8.  Start salting.
Soak and salt until ∆ 9 is down, which is ∆ 10 pointing at nine o'clock.
Shut off all burners, and crash cool to a bright orange kiln chamber.

Usually this takes 10 to 12 hours, sometimes a bit longer.  We try to salt after dusk so the vapor is not as noticeable.  If passers by call the UFD, they have to come.  We always call them before salting to give them a heads up.

* There are two schools of thought on reduction.  Some potters do a "body" reduction at this temperature (for a given amount of time) and then ramp in a "neutral" atmosphere until doing a "glaze" reduction at ∆ 8,or 9.  We favor ramping in a reduction atmosphere. There are pros and cons about this in terms of being green and "wasting fuel." We try to strike a middle position.  The kiln results are the priority. A bad firing is neither green or efficient.

Next: Ramp and Reduction