Smelt iron in a bloomery

Feed ore and charcoal into the furnace for hours of pumping to win a glowing spongy lump of real iron.

a craft to master⏳ a season of triestradition — not yet hand-tested

This is the summit of the whole book. Every knife, nail, axe, and hinge starts with this one hot afternoon: rock and charcoal go in the top, and if you keep the air coming, a lump of real iron comes out the bottom. The lump is called a bloom — a spongy, glowing mass of iron mixed with waste.

Be ready to fail. Almost everyone's first smelt makes only slag (melted rock waste) and lessons. Ancient smiths failed too. Plan for a season of tries, change one thing at a time, and write down what you did each run.

You need

• A bloomery furnace, built and fully dried — a clay chimney about 1 metre tall with an air pipe (the tuyere, say "TWEE-yair") low on one side.
• Roasted, crushed ore, 10–20 kg. Roasting means baking the raw ore in an open wood fire for an hour — it drives out water and makes it crumbly. Then smash it to pea-size bits, about 1 cm.
• Charcoal, 30–60 kg, broken to walnut-size lumps. Yes, that much. Charcoal is the fuel AND the chemical that frees the iron.
• Bellows and at least two people. You will pump air steadily for 4–6 hours. Take turns.
• Long tools: a green-wood poker, a metal or green-wood rake, and stout wooden tongs for grabbing the bloom.
• A heavy wooden mallet or stone hammer and a big flat stone for squeezing the hot bloom together.
• Buckets of water and clear ground — for burns and stray fire, never for pouring into the furnace.

Steps

1. Preheat. Fill the furnace with dry wood, light it, and let it burn down for 1–2 hours. This dries the clay and warms the walls.
2. Switch to charcoal. Fill to the top with charcoal only and start pumping. Steady, calm strokes — a rhythm you can hold, not a sprint.
3. Start charging. When the charcoal at the top sinks by about a hand's depth, add a layer: roughly 1 kg of charcoal, then 1 kg of ore, spread evenly. Keep this 1-to-1 ratio by weight, and keep topping up each time the top sinks a hand's depth.
4. Keep the blast steady for 3–5 hours. The zone in front of the air pipe should glow bright yellow-white — around 1,200 °C. If the glow looks merely orange, pump harder or check the pipe for blockage.
5. Tap the slag. Melted rock waste pools at the bottom, and if it rises to the air pipe it drowns the blast and kills the smelt. When the furnace gurgles or the air seems to choke, poke a hole low through the clay plugging the front arch — the door you built into the base — and let the liquid slag run out onto dry bare ground like black-orange syrup. Stand to the side, never in front of it, and wear nothing that a splash can stick to. When the run slows, close the hole again with a wad of soft clay. Tap as often as the furnace asks; a plug is cheap and a drowned tuyere ends the day.
6. Finish and pull the bloom. After the last ore is in, keep pumping until it burns down, then break open the furnace front. Reach in with tongs and drag out the bloom — a glowing sponge, maybe fist-size to head-size.
7. Consolidate at once. While it is still yellow-hot, hammer it on the flat stone. Squeeze out slag, weld the sponge into a solid lump. Reheat in the coals and hammer again, several rounds. This lump is your iron.

Watch out

• Carbon monoxide. The furnace breathes out an invisible, odourless poison gas. Work outdoors only, stand upwind, and never lean over the top breathing the fumes.
• Steam explosions. Water touching molten slag flashes to steam violently. Keep water for people and grass fires, never the furnace.
• Burns and fire. The bloom is around 1,200 °C — it sets wooden tongs smouldering. Clear dry grass for 3 metres around before you start.
• All slag, no bloom? Usual causes: ore too poor (test richer rock), air too weak (bigger bellows, tighter pipe), or ore charged too fast (lean toward more charcoal).
• Bloom crumbles when hammered? It cooled too much. Hammer only at bright yellow heat; reheat often.

How it works

Charcoal burning with limited air makes carbon monoxide gas. That gas pulls the oxygen out of the ore — ore is just iron rusted into rock — leaving iron metal behind. The furnace never gets hot enough to melt iron (that needs 1,538 °C); instead the freed iron specks stick together into a sponge, while the rock melts into slag and drains away.