Knead your clay thoroughly before placing it on a potter's wheel. Kneading removes air pockets in the clay. If air pockets are present during the firing process, the trapped air will expand and cause your pots to break. Large air pockets can even cause pots to explode in the kiln, which can damage other pieces of pottery.
Completely form, shape and trim your pots before the clay dries. During this phase, the clay should be leather hard--soft enough to cut and trim, yet hard enough to support its own weight. Allow the pots to dry completely before firing, because water vapor can cause the clay to crack or break as it heats.
Fill the bottom shelf of the kiln with pieces of similar height. Place support posts near the four corners of the kiln and place another shelf on the supports. If you are firing in a large kiln, you may also need to place support posts in the center. Continue this process, filling the kiln as fully as possible.
The initial firing is called a "bisque" firing. Place pyrometric bisque cones where they can be seen without completely opening the kiln's lid or door. These cones come in sets of three, and will melt in succession as the pottery reaches the bisque stage.
Heat the kiln to approximately 1600 degrees Fahrenheit. If you have an electric kiln with control switches, fire on the low setting for an hour, then turn the switch to "medium" for an hour before firing at full temperature. Check the cones every few hours to ensure that the bisque firing is properly progressing. A bisque firing will take approximately 16 to 18 hours.
Allow the pots to cool for several hours before removing them from the kiln. Use a damp cloth to remove any dust that would prevent glazes from properly adhering. Glaze or stain the pots as desired. Most commercial glazes come with a cone rating, which indicates the needed length and temperature of the second firing.
Brush a thin layer of kiln wash on the shelves to keep glazed pots from sticking to them. Load the glazed pots into the kiln in the same manner as you used for the bisque firing. Make sure that the pots do not touch. If some pots require a higher firing temperature, place these pots on the bottom shelves. Place the appropriately rated cones where they can be easily seen.
Glaze firing temperatures vary according to the glazes and stains used, but the standard temperature is about 2,300 degrees Fahrenheit. Fire for 16 to 18 hours. Let the pots cool for 48 to 72 hours before removing them from the kiln.