炉火纯青 Trad. 爐火純青
lú huǒ chún qīng
lit. the stove fire has turned bright green (indigo) (allusion to Daoist alchemy) (idiom)
fig. (of an art, a technique etc) brought to the point of perfection
The phrase "炉火纯青" (lú huǒ chún qīng) translates to "the furnace fire is pure blue" in English. It is an idiomatic expression that means to reach a high level of skill or mastery in a particular craft or discipline. The imagery of a pure blue flame suggests a state of perfection and expertise, indicating that someone has achieved a refined and exceptional level of proficiency.