Steel doesn't come with a temperature readout. It comes with a glow, and the smiths who last a lifetime learn to read it the way a cook reads a steak.

The scale

Faint red at 500°C, cherry red at 815, orange at 980, and white somewhere past 1100 where the steel is quietly burning. Between cherry and bright red is where ninety percent of the work happens.

Why it matters

Forge too cold and you're just beating a stubborn bar. Forge too hot and you burn the carbon out of the edge — the steel turns to a sparkler, and no quench will save it. The color is the whole game.