Today I get to open my kiln. I fired it Monday – an anxious firing – and now the pyrometer reads about 450 F on the top and 650 F on the bottom. I opened the damper and the top port so it will have a little more air in, but will still cool slowly. About 3:00 I will knock loose the restraining bars that hold the door in place and crack open the top of the kiln so heat will flow upwards out of the top. AT 8:00 PM I will open the door and see what I’ve got. For potters, opening a kiln like this is better than Christmas. It doesn’t matter that I don’t want to keep the stuff – it’s an exoneration of the whole irrational process and the completion of two months of work.
I don’t make a lot of work compared to some functional potters, and fire my 24 cubic foot kiln only 6 times a year. There’s a huge amount of work invested in each load – many small pieces – and there are firing variables that make each load distinctive. There are pots that have color or flash that I simply can never duplicate. If I fired the kiln once a week I might be better able to produce specific effect. I do keep careful records, and try to use them to make adjustments and conserve fuel.
I said it was an anxious firing – that’s because I forgot to order propane and wasn’t sure that I would have enough. No space here to go into the physics of propane firing, but when vapor is being drawn into the burners too rapidly it can supercool the whole liquid puddle of propane in the tank and cause “freeze up.” I’ve experienced this once, and it’s terrible. Your kiln is almost at temperature and it stalls, nothing works…. that time, the tank was covered with more than an inch of dense, hoary frost. I had to get a delivery the next day, and start over- gas and time squandered……
The first shelf goes in carefully. The hardbricks beneath must be cleaned and fresh wadding applied so the shelves can be leveled. Space between the pots lets the flame and vapor bless every pot equally, nothing nastier than a dry side on a good pot.
Even the kiln posts must be wadded to make precise leveling possible. After many recipes for kiln wadding, I have settled on 1 part alumina hydrate and 1 part Helmar kaolin by volume. I make a batch during each firing so I will have nice, plastic wads to use a few months later. It gets better to handle each week that it ages. I have added wheat flour – nice for workability but it must be frozen if there is excess because it spoils. I have also added sawdust, which has good properties of you are using larger wads. Because I make really small wads, I prefer to just use the Helmar-Alum.Hydrate wadding. It takes 2 hours to shape all the wadding for a firing…. many friends have helped with this over the years. FYI, Helmar kaolin is a high-alumina kaolin mined in Idaho. Great stuff for salt-firers, I also use it in my flashing slip, Helmar and EPK, equal parts by volume, skim milk thin. My wads pop off clean with almost no sanding – one less thing to do before pricing and packing the pots.
Tallest pieces go into the top of the kiln. I have some solid silicon carbide soaps that make a stable base for high shelves. Every load is different – I was a little concerned about having a shelf up this high but this firing would prove to have good top-bottom heat distribution in spite of it.
I have great Buzzer burners and Buzzer nozzles at this point in my salt-firing career. No safety equipment for us purists – I just live in the kiln shed for 16 hours. I love the quiet early part of the firing, calm blue flame….. I am usually cleaning my tools, my studio, having a rare cup of coffee. Later, when the kiln roars, its’ power can be frightening. Once, during a terrible storm, I had 24″ flames shooting out of the burner ports during wind gusts. I blew up the first kiln I ever built – the memory of that explosion lives in every cell of my body.
But how else can make my pots?