Firing the PrattMWP salt kiln

Salting and cooling-

At ∆8 we begin to salt the kiln.  We continue until we have reached ∆9 or 10.  Some potters adjust the damper during salting. We keep the damper setting still.  We can discuss other options later.

We use a salt mixture of 2 parts salt, 1 part sawdust, 1 part fine ash. There are many recipes.  We play with this recipe from time to time. We do not use sodium bicarbonate or similar materials.  On occasion we throw in some borax, but I like the addition of ash better.  It is light and more likely to carry through the kiln with the vapor than other material.  The sawdust adds reduction material and ash.

The mix is scooped into a length of angle iron that will fit through the salting port, the opening of which is the size of a soap (a straight brick cut in half length wise).  Slide the angle iron into the kiln and turn.  You will develop a rhythm or schedule for the saltings- two troughs each side, every 8 minutes, for instance.  Continue until you have a good glaze buildup and/or reach ∆9/10.

After a salting or two, pull a test ring to gauge the glaze buildup.  We use a rod (rebar) to hook the ring from inside the kiln.  Drop the ring into a bucket of water.  When cool dry it off and check the glaze.
As the kiln ages and "seasons," it will require less salt to get the glaze buildup.  I have read some different notions about this, but I find it to be so.

After we have reached the temperature and glaze desired, we shut the kiln down.  Turn off all burners.  What you do now will have an impact on the glazes.  We "crash cool," or open all ports and damper to get the kiln to cool down quickly.  The idea is to get the glazes to "freeze," resulting in a higher gloss.  You can play with this to see what effects you can get.  If you do crash cool, drop to 2150˚F or so. Do not go below 1950˚!  The chamber should look bright orange at its coolest.  This will take a shorter time than you think.  After cooling, seal the kiln tightly, closing all ports and damper.  Then, patience. Open the kiln when you can comfortably place your hand in the upper part of the chamber.  Wait a good 24 to 36 hours to do this!  There is a common rule of thumb for heating and cooling.  Take as much time to cool as you took to fire.  We fire rather fast so we keep to the 24-36 hour rule.  More exactly, after 24 hours, we open the damper and spy ports and wait another 10 -12 hours.  The results are worth the wait!!!

Next post about salt firing- some alternate approaches using salt.