This common flame is known as Spiritual Fire, which generally uses a cultivator's internal Spirit Power as fuel. The more Spirit Power there is, the longer the fire burns; the purer the Spirit Power, the higher the temperature of the Spiritual Fire when it burns.
Theoretically, the higher the Cultivation Level, the stronger the flame that appears, but in reality, cultivators with higher cultivation levels rarely use this method for alchemy or Artifact Refining.
Instead, they choose the second method, which is to use furnace cauldrons to refine items.
Although a furnace cauldron may look like a simple stove, a true furnace cauldron actually has its own universe inside.
A true furnace cauldron has many formations inscribed within it and also has the capability to collect and store Spiritual Fire, such as the most common Core of Earth Fire and Celestial Fire.
