As the title says. You can fire pottery or melt copper ores using the pit kiln, but if you break the kiln by holding down the "break" button you can extinguish the fire and slowly make progress on breaking the fuel stack for the pit kiln. You can also briefly see if the pottery has fired between when the fire is extinguished and when it is relit automatically, meaning you know when to break the pit kiln and you can reclaim the fuel from it while still having fired or melted contents. This seems to happen around the 40 second remaining mark.