Make bellows

Sew a leather-and-wood air pump, because metal-melting fire must breathe harder than lungs can blow.

takes patience⏳ two daystradition — not yet hand-tested

An open charcoal fire reaches maybe 800–900°C. Melting metal out of rock needs 1100°C and more. The only difference is air: the harder a fire breathes, the hotter it burns. You could blow through a tube, and people once did — but lungs tire in minutes, and a smelt takes hours. A bellows is a leather bag between two boards. Squeeze it and it blows; lift it and a flap valve lets it refill. It never gets dizzy.

You need

• Two flat boards, teardrop shaped, about 50 cm long and 30 cm wide at the fat end — the top and bottom of the pump. Split and smooth them from any sound wood.
• Soft tanned leather, one hide's worth — the flexible sides. Stiff rawhide cracks; it must be real leather.
• Pitch or glue — every seam must be airtight. A leaky bellows feeds the seam, not the fire.
• Small nails, wooden pegs, or strong sewing (awl and sinew or cord) — to fasten leather to wood.
• A nozzle tube with a thumb-thick hole: two sticks grooved down the middle and glued face to face, or a straight tube of dried clay.
• A palm-sized scrap of soft thin leather — the one-way valve.

Steps

1. Cut both boards to the same teardrop shape, with the points where the nozzle will go.
2. Make the valve in the bottom board: bore or burn a hole about 3–4 cm wide near the fat end. On the inside face, tack the soft leather scrap over the hole along one edge only — it must swing free like a pet door. Lift the board: air comes in. Press: the flap slaps shut.
3. Fix the nozzle between the two pointed ends, aiming forward, and pack every gap around it with pitch.
4. Hinge the pointed ends together with a strap of leather so the boards open and close like a clam.
5. Cut a long strip of leather wide enough to wrap the open gap all around the edges, letting the fat end open a good 20–30 cm.
6. Fasten the leather to both board edges: fold the edge over for strength, then nail, peg, or sew it down tight, working around from the nozzle. Paint every seam with warm pitch inside and out.
7. Add a handle to the top board — a stick or a leather loop — and a way to hold the bottom still (kneel on it, peg it down, or add a second handle).
8. Test it. Pump toward dust or a feather; you should feel a steady punch of air at the nozzle. Then hunt leaks: pump slowly with your wet lip or a licked finger near each seam. Any cool hiss gets more pitch.
9. If you can, make a second bellows. Two, pumped in turn, give the furnace one unbroken breath — that is what smelting really wants.

Watch out

• Leaks are the number one failure. A bellows that hisses feels busy but starves the furnace. Seal, test, seal again — a tight small bellows beats a leaky big one.
• The valve flap must be soft and free. Too stiff and it won't lift to let air in; tacked on more than one edge and it can't move at all. Thin soft leather, one edge, that's the whole trick.
• Fire eats nozzles. Never push the wooden tip into the coals. At the furnace, the bellows blows into the outer end of a clay tube (called a tuyere — a fireproof clay pipe through the furnace wall). Keep the wooden nozzle a finger-length back from any glow.
• Sparks blow back. Air out means the fire spits. Kneel to the side of the blast line, never in it, and keep the leather sides away from stray coals.
• Untanned or dried-out hide splits within an hour of work. Use properly tanned leather, and grease it now and then to keep it supple.

How it works

Pressing the boards shrinks the bag, and the trapped air has only one exit: the nozzle. Lifting the boards grows the bag, the pressure inside drops, and outside air pushes the flap open to refill it — the flap is a door that only opens inward. More air means more oxygen reaching the charcoal each second, and burning faster is exactly what burning hotter means.