Bloomery

A bloomery is the earliest type of furnace used to smelt iron from its ore, producing iron by direct reduction at temperatures high enough to separate metal from slag but too low to fully melt the iron itself, leaving behind a spongy mass called a bloom that mixes iron with trapped slag. Smiths worked the still-hot bloom by repeated hammering to squeeze out as much slag as possible and consolidate the remaining iron into a usable, workable mass, a laborious process very different from the continuous liquid-iron output of a later blast furnace. Bloomeries appeared independently in various parts of the ancient world, including the Near East, sub-Saharan Africa, South and East Asia and Europe, and remained the dominant iron-smelting technology for well over a thousand years before the blast furnace, which fully melts the iron and can be operated continuously, began to supersede it in medieval Europe.