Bellows — two wooden boards connected by leather, with valves. Squeeze — air goes to forge. Release — air draws back. Rhythm: squeeze-release. Coal goes from red (700°C) to white (1,200°C).
Types
Hand — classic. Stand and pump. Foot — hands free. Foot pumps, hands forge. Rotary (crank fan) — most efficient, but not all communities allow it (mechanism = worldly?).
Why 1,200°C
Horseshoe: 800°C. Knife: 900°C. Forge welding: 1,100-1,200°C. At that temperature, two pieces of steel become one. No welding machine. Just fire and hammer.