Smithing

Look at the steel in shade, out of direct sun — work under a roof or hang a cloth. Judge the colour of the metal itself, not the fire around it. With practice, colours are consistent to about ±50 °C.

A forge fire is not a bonfire. It is a small, deep, compact heart of burning fuel with air driven into its base, and the steel goes into the heart, not on top.

• Work in the reducing zone. Just above the air inlet (the tuyère), oxygen is abundant and the fire burns steel, building thick scale. A little higher, in the middle of the heap, the oxygen has been used up and the fire is rich in carbon monoxide — that zone heats steel without eating it. Bury the work there, with fuel above it.
• Heat slowly and evenly. A thick bar heated fast is orange outside and black inside, and forging it tears the core.
• Fuel: charcoal is clean and contains no sulphur, which makes steel brittle; it burns fast and needs constant feeding. Coal lasts longer but must be burned to coke first, and sulphurous coal spoils welds. See the charcoal guide.
• Clinker — the glassy lump that forms above the tuyère when coal or impure charcoal burns — chokes the air. Lift it out when the fire stops getting hot.
• Keep the fire small. A large fire wastes fuel and heats the smith more than the steel.

Iron with less than about 0.3% carbon is soft and will not harden however it is quenched. Iron with 0.6–1.2% carbon hardens into a tool. They look identical. Scrap is where early smiths get their steel, and knowing which scrap is which decides whether a tool holds an edge.

Every forged object is a sequence of a few basic moves.

• Drawing out — lengthening and thinning. Hammer on the far edge or the horn of the anvil, which acts as a blunt wedge, then flatten the ripples on the face. Turn the bar a quarter turn after every few blows to keep it square.
• Upsetting — shortening and thickening. Heat only the end you want thicker, stand the bar on end on the anvil, and strike down. Quench the part that should not bulge.
• Bending — over the anvil horn or edge, or in a bending fork in the hardy hole. Heat only the bend.
• Punching — a hot punch driven halfway through from one side, the bar flipped, and finished from the other over the pritchel hole. Cool the punch often, or it softens and mushrooms.
• Cutting — over a hardy (a chisel wedge in the anvil's square hole) or with a hot chisel. Never strike through onto the anvil face.
• Twisting — heat evenly along the length to be twisted, clamp one end, turn the other with a wrench.

Forge welding joins two pieces:

1. Shape the ends to be joined into short tapers — scarfs — so the joint closes from the centre outward and pushes out scale.
2. Bring them to orange heat and sprinkle flux — borax — on the joint faces. Flux melts, dissolves the scale and seals the surfaces from air.
3. Return to welding heat: bright yellow to white, the surface looking wet and running.
4. Bring them together fast on the anvil, and strike light, quick blows first from the centre outward, then heavier.
5. Reheat and hammer again to consolidate. A weld that shows a dark line has not taken.

Carbon steel can be made hard, tough, or soft, and the difference is entirely heat and cooling rate.

Normalise first. Forging leaves coarse, uneven grain. Heat the finished piece to just past non-magnetic and let it cool in still air. Do this three times. It relieves stress and refines the grain, and a tool normalised first is far less likely to crack in the quench.

Harden.

1. Heat evenly to one shade past non-magnetic — bright cherry red.
2. Quench in oil warmed to about 50 °C — warm to the touch. Plain vegetable oil works. Use at least 4 litres for a knife-sized piece.
3. Plunge straight down, point first, and move it up and down, not side to side, which warps blades.
4. Water and brine quench faster and harden more — and crack most carbon steels. Use them only on simple high-carbon steel you have tested.
5. Test with a file. On hardened steel the file skates without biting.

Temper immediately — within the hour. Hardened, untempered steel is as brittle as glass and can crack sitting on the bench. Polish a patch bright with sandpaper or a stone, then heat gently and evenly — on a hot iron bar, or in an oven — and watch the oxide colours run. Stop when the edge reaches the colour for the job, and quench to hold it.

• Every piece is hot until proven otherwise. Steel at 400 °C looks exactly like steel at room temperature and burns to the bone. Pick up by the end that was never in the fire. Put hot work down in one fixed place, pointing away from the walkway. Check a doubtful piece by sprinkling water on it, never by touch.
• Eyes. Scale flies off at every blow and sparks come off the grinder. Wear eye protection; a scale fragment in the eye is common, and a hot one scars the cornea.
• Galvanized metal gives off zinc oxide fumes when heated — metal fume fever: fever, chills and aches within hours. Never heat galvanized steel. Strip the zinc first by soaking it in vinegar or dilute acid outdoors until the grey coating is gone and bare steel shows.
• Quench oil fires. Hot steel can ignite quench oil. Keep a metal lid beside the tank to smother it; quench deep and fast so the part is below the surface; never throw water on an oil fire.
• Carbon monoxide from a forge under a low roof or indoors. A smithy needs a hood or a high open roof. See the carbon monoxide section of the fire guide.
• Hammer and chisel faces mushroom with use and shed razor-sharp chips. Grind the mushroom off before it spalls.
• Hearing. An anvil's ring causes permanent hearing loss over years. A magnet or a chain on the anvil deadens it; so does ear protection.