Smelting is a method for extracting a pure metal from an ore (an ore is a rock made up of metals and other minerals). In smelting, a chemical transformation may be used to purify the metal by changing the oxidation state of metals in the ore (we’ll get into more detail on what an oxidation state is later in the book). The smelting of iron dates back to ca. 1000 B.C.E. (or maybe even earlier), and it typically involves first heating the raw material in a furnace called a bloomery. This produces a soft iron material that can be shaped. A hammer is often used to remove other impurities from the soft metal before allowing it to harden to form a relatively pure form of iron.