Gather stoneware to be fired in a pit. High-fire stoneware clays yield the best results.
Dig a pit or set up an oil drum for firing. If it is an open pit, you will need to use a fire ring around the outside of the pit for safety.
Purchase or gather appropriate combustibles or chemicals to fuel the fire in the pit. The coloring effects that show up on your stoneware will vary according to the types of combustibles you add to the fire when firing it.
Ignite the combustibles to start a fire in the fire pit. Temperature, the placement of stoneware within the pit, the combustibles, and timing affect the firing results.
Place the stoneware in the firing pit. Use safety gloves and a mask. Position the stoneware in the pit with combustibles around it to create the colors and other effects you desire. Reposition the stoneware within the pit to change the factors that affect the final result. Be careful not to damage the stoneware while repositioning it during the firing process.
Monitor and maintain an even, steady high-heat temperature within the fire pit during the firing process. Add more combustibles as needed. Allow a flow of oxygen if you're using a covered oil drum. Be careful not to create a sudden increase in heat or flame or to let the temperature get too cool inside of the pit. The structure of the end stoneware item and its usability and strength depend greatly on how the firing process goes and requires an even, steady distribution of high heat.
Remove the pit-fired stoneware from the fire pit using safety gloves. Cool the stoneware down. Proceed with any additional finishing steps that you may want to add to the pit-fired stoneware.