Lithium does not simply burn. It moves through a sequence of distinct physical and chemical stages, and each one is written in colour. Hold a sliver of lithium metal in a flame and the first thing to disappear is the silver lustre. The surface tarnishes almost instantly into a dark crust of lithium nitride and lithium oxide. Lithium is the only alkali metal that reacts with atmospheric nitrogen at room temperature, so the air itself attacks it before any fire is involved. The progression unfolds in stages: - Melting at 180.5 °C, where the metal collapses into a bright liquid bead - Ignition, where the bead sustains a vivid crimson flame - Full combustion, where the flame shifts to an intense white as solid Li2O particles incandesce - Burnout, leaving a pale oxide residue behind The crimson is atomic, not thermal. Heat promotes lithium’s single 2s valence electron into the 2p orbital. When it relaxes, it emits a photon at 670.8 nm, deep in the red. That single dominant line is why l...