Q: I recently purchased an old JenKen kiln to fire my hand built pottery.... This 40+ year old kiln has 2 knobs, each with a low, medium and high setting. How
do I know how long I leave the kiln on each of the 3 settings for a high fire
greenware to bisque firing, and then a glaze firing? I'm just not sure of the
timing and do not want to over or under fire my pieces. I'm so excited to do this
yet so nervous, and the nervous side is winning....
A: Hey, don't think you're alone in this! I think all of us have at least some anxiety when firing a "new" kiln for the first time, no matter how long you've been doing it!
For a bisque firing, load the kiln sitter ( see How to Use a Kiln Sitter) with a cone or rod for the cone you want to fire to, e.g. a ^04 cone or rod for an earthenware bisque.
If by chance your kiln doesn't have a kiln sitter, load a cone pack and place it where you'll be able to see it from a peek hole when you stack the kiln.
Again, we're talking a bisque load --- once the load is stacked, close the kiln. Put the bottom-most switch to low. Leave at that setting for one to two hours (depending on humidity -- more moisture in the air, give more time).
Turn the top switch to low, and heat for four hours with both switches on low.
Turn the switches to medium and heat two hours.
Turn the switches to high, and fire until temp is reached. The kiln sitter should automatically shut the kiln down, but if yours doesn't have a sitter, you'll need to keep an eye on the cone pack, especially once the kiln is incandescent inside.
Glaze firings are a bit simpler. The one problem you may encounter is reaching temp if you are firing above earthenware ranges. Many older used kilns can have trouble reaching ^5-^6. They just don't have enough insulation to be really efficient.
If your kiln does have trouble reaching temp, you may need to replace your kiln elements. You might also consider adding more insulation by wrapping a refractory blanket (e.g. Kaowool) around the outside of the kiln, being sure not to cover the switch boxes, kiln sitter, and peep holes.
For a glaze firing, after loading the kiln turn both switches to low for two hours.
Turn the switches to medium for two hours.
Turn the switches to high until the kiln reaches temp.