Metalworking
Why This Matters
Metal is the material that separates the Stone Age from everything that follows. A stone axe can fell a tree, but a steel axe does it in a quarter of the time. A wooden plow scratches the surface, but an iron plow turns deep soil. Metal tools make metal tools, creating a compounding cycle of capability. Nails, knives, axe heads, saw blades, hooks, hinges, wire, cooking pots, needles — the list of things you cannot make without metal is essentially the list of everything a civilization needs. This article teaches you to work metal from scrap or from raw ore using a charcoal forge you build yourself.
What You Need
To build a forge:
- Firebrick, clay bricks, or a thick-walled stone enclosure (at least 30 cm tall)
- A steel pipe (3-5 cm diameter, 30-50 cm long) for the tuyere (air inlet)
- Bellows or a blower (see Bellows section below)
- Charcoal — at least 10 kg for a working session (see Charcoal Production)
- A flat, heavy steel surface for an anvil (railroad track section, large hammer head, thick steel plate)
- A hammer (1-1.5 kg for general work, 2-3 kg for heavy forging)
- Tongs (or pliers as a temporary substitute) to hold hot metal
- A container of water for quenching (a steel bucket, trough, or deep pot)
- A container of oil (vegetable oil, motor oil, or animal fat) for quenching
- Safety: leather gloves, eye protection, long-sleeved natural-fiber clothing (synthetic fabrics melt into skin)
For smelting from ore:
- All the above plus:
- Bog iron ore, magnetite sand, or hematite (iron-bearing rock)
- A taller furnace (bloomery) built from clay and stone
- Significantly more charcoal (50-100 kg per smelt)
- A heavy hammer or large rock for consolidating the bloom
- Patience — your first smelt may fail
Building a Charcoal Forge
A forge is simply a contained fire with forced air. The bellows push air through the charcoal, raising the temperature from about 700 degrees C (unforced charcoal) to 1300+ degrees C (forced). This temperature difference is what makes metalworking possible.
The Firepot
Step 1 — Build a U-shaped or circular enclosure from firebrick, clay bricks, or stacked stones. Interior dimensions: roughly 40 cm wide, 40 cm deep, 30 cm tall. The floor should be flat and heat-resistant (a thick clay slab or fire brick).
Step 2 — At the bottom of one wall, insert your tuyere — a steel pipe angled slightly downward into the fire area. The pipe should enter about 5-8 cm into the interior, positioned so the air blast hits the center of the firepot. The tuyere angle should be about 20-30 degrees below horizontal so that ash and slag do not flow back into the pipe.
Step 3 — On the exterior end of the tuyere pipe, connect your bellows or blower. The connection does not need to be airtight — close-fitting is sufficient.
Step 4 — Fill the firepot with charcoal to a depth of about 15-20 cm. Light the charcoal from the top. Once it is burning well (5-10 minutes), start pumping the bellows gently. You should see the charcoal glow brighter orange, then yellow, then white at the center. White-hot charcoal is approximately 1200-1400 degrees C — hot enough to forge iron and steel.
Building Bellows
If you have no mechanical blower (a hair dryer, fan, or leaf blower), you need bellows. The simplest effective design is the double-lung bellows:
Step 1 — Build two rectangular frames from wood, each about 40 cm wide and 60 cm long. These are the “lungs.”
Step 2 — Cover each frame with a flexible, airtight material: leather is ideal, but tightly woven fabric sealed with pine pitch or animal fat also works.
Step 3 — Hinge both frames at the back (the end away from the forge). The front of each frame narrows to a nozzle that connects to the tuyere pipe.
Step 4 — Add a one-way flap valve to the air intake hole on the top of each lung (a piece of leather that covers the hole and lifts when you pull the lung open, then seals when you push it closed).
Step 5 — Operate by alternately pumping each lung. When one is pushing air into the forge, the other is drawing in fresh air. This provides a continuous blast.
A simpler alternative: a single-action bellows made from a large bag (leather or heavy canvas) with a wooden nozzle. Squeeze the bag to push air into the tuyere, open and fill, squeeze again. Less efficient but much easier to build.
The simplest possible option: a length of pipe or hollow bamboo that you blow through directly into the tuyere. Exhausting for the operator but works for small jobs.
Understanding Heat Colors
When you heat steel, its color tells you its temperature. This is your thermometer:
| Color | Temperature | What You Can Do |
|---|---|---|
| Black heat (no visible color) | Below 400 degrees C | Nothing useful — metal is not workable |
| Dark red (barely visible in shade) | 400-500 degrees C | Tempering only |
| Cherry red | 700-800 degrees C | Forging begins — metal moves under the hammer |
| Bright cherry red | 800-900 degrees C | Good forging heat for most work |
| Orange | 900-1000 degrees C | Ideal forging heat — metal moves easily |
| Yellow | 1000-1100 degrees C | Maximum forging heat — be careful, metal is close to burning |
| White | 1200+ degrees C | Welding heat — two pieces of iron will fuse. Also the “burning” point where iron crumbles |
Critical rule: Always work in shade or dim light so you can see the colors accurately. In direct sunlight, you cannot distinguish cherry red from orange, and you will overheat your steel.
Working with Scavenged Metal (Recommended Starting Point)
In a post-collapse scenario, scavenged metal is far easier to work than smelting from ore. Every ruined building, car, and appliance is a source of high-quality steel.
Best Sources of Scavenged Metal
| Source | Type of Metal | Best Used For |
|---|---|---|
| Leaf springs (vehicles) | High-carbon steel (1075-1095) | Knives, axes, chisels — excellent edge-holding |
| Coil springs | High-carbon steel | Knives, punches, springs |
| Railroad spikes | Medium-carbon steel (1020-1040) | Hooks, nails, small tools — soft, easy to work |
| Rebar | Mild steel (low carbon) | Tongs, pokers, handles — bends easily, will not hold an edge |
| Ball bearings | High-carbon chrome steel | Excellent for cutting tools if you can forge them |
| Files and rasps | High-carbon tool steel | Superb knife and chisel material |
| Lawnmower blades | Medium-carbon steel | Machetes, large knives |
| Car axles | Medium-carbon alloy steel | Anvil tools, hammer heads |
How to Identify Carbon Content
You need to know the carbon content to decide how to heat-treat the metal:
Spark test: Hold the metal against a spinning grindstone (or draw a file across it quickly in the dark). Watch the sparks:
- Mild steel (low carbon): Long, straight orange sparks with few or no branches
- Medium carbon: Shorter sparks with some forked branches
- High carbon: Short, bushy sparks with many branches and tiny white bursts at the tips
- Cast iron: Dull red sparks, very short — cannot be forged (it shatters)
Bend test: Clamp in a vise and bend. Mild steel bends easily. Medium carbon bends with effort. High carbon cracks or snaps. Cast iron shatters.
Method 1: Forging with a Charcoal Forge
The Four Basic Operations
Every forging task is a combination of four fundamental operations. Master these and you can make anything.
Drawing Out (Making Metal Longer and Thinner)
Step 1 — Heat the workpiece to bright cherry red to orange (800-1000 degrees C).
Step 2 — Place on the anvil and strike with overlapping hammer blows, moving along the length of the piece. Each blow should land slightly ahead of the last.
Step 3 — Rotate the piece 90 degrees and hammer the adjacent face. This prevents the metal from spreading sideways when you want it to stretch lengthwise.
Step 4 — Reheat whenever the color drops below cherry red. Hammering cold metal wastes your energy and creates internal stress cracks.
Used for: making points (nails, spikes), tapering knife blades, stretching bar stock.
Upsetting (Making Metal Shorter and Thicker)
Step 1 — Heat only the area you want to thicken to orange heat (900-1000 degrees C). If you heat the whole bar, the whole bar will upset and you lose control of the shape.
Step 2 — Hold the bar vertically and hammer straight down on the top end, driving the hot section into itself.
Step 3 — If the bar starts to bend or buckle sideways, flatten it on the anvil face and try again. Buckling means the hot zone is too long — heat a shorter section.
Used for: making nail heads, bolt heads, thickening a section before punching a hole.
Bending
Step 1 — Heat the area where you want the bend to bright cherry red.
Step 2 — Position the hot section at the edge of the anvil and hammer the overhanging portion downward. For a sharp 90-degree bend, hammer right at the anvil edge. For a gentle curve, start hammering farther from the edge.
Step 3 — For bending around a form (like making a hook or ring), use a horn on the anvil or a round bar clamped in a vise.
Used for: hooks, handles, hinges, rings, chain links.
Punching (Making Holes)
Step 1 — Heat the workpiece to orange heat where you want the hole.
Step 2 — Place on the anvil and drive a punch (a tapered steel rod) partway through — about halfway.
Step 3 — Flip the workpiece over. You will see a dark spot where the punch pushed the metal thin. Drive the punch from this side to meet the first hole.
Step 4 — Place over the pritchel hole (a round hole in the anvil) or over the open edge and drive the slug out.
Used for: nail holes in hinges, eye holes in axe heads and hammer heads, rivet holes.
Making Essential Tools
A Simple Knife (From a Leaf Spring or File)
Step 1 — Cut a section of leaf spring about 25-30 cm long using a hot cut (heat the cut line to yellow and strike a chisel through it on the anvil edge) or a hacksaw.
Step 2 — Heat to orange and draw out one end to form the blade. Flatten and taper to roughly 3-4 mm thick at the spine, tapering to about 1 mm at the edge line. Do NOT sharpen yet — leave the edge about 1 mm thick (the “edge bevel” is ground after heat treatment).
Step 3 — Form the tang (handle portion) by drawing out the other end to about 8-10 mm diameter, 10-12 cm long. This will be driven into a wooden handle.
Step 4 — Heat treat (see Heat Treatment section below).
Step 5 — Grind or file the edge bevel to a sharp edge. Push a wooden handle (hardwood, with a hole drilled or burned through) onto the tang and peen the end over to lock it in place.
Nails
Step 1 — Cut a length of mild steel rod (6-8 mm diameter rebar or wire). Heat 3 cm of one end to orange.
Step 2 — Draw the hot end to a tapered point over about 2 cm.
Step 3 — Reheat. At the point where you want the nail head, place the rod in the nail header (a thick plate with a hole slightly larger than the rod) or over the pritchel hole so the point sticks down and 5-6 mm of the shaft sticks up.
Step 4 — Hammer the protruding end to mushroom it into a head. 3-4 blows.
Step 5 — Quench in water. A skilled smith can make a nail in under 60 seconds.
An Axe Head
Step 1 — Start with a piece of medium or high-carbon steel about 15 cm long, 5 cm wide, and 2 cm thick (a section of leaf spring works well).
Step 2 — Heat the center section and punch a rectangular eye hole approximately 3 cm x 2 cm for the handle. Drift (enlarge) the hole by driving a tapered steel bar through it, rotating the workpiece.
Step 3 — Draw out one end to form the blade — taper it to about 8-10 cm wide and 3-4 mm at the edge (leave the edge thick for now). This is the bit.
Step 4 — Shape the poll (back end) into a flat, squared-off striking surface.
Step 5 — Heat treat the bit only (see Heat Treatment). The poll should remain softer so it does not chip.
Step 6 — Grind or file the edge. Fit a hardwood handle through the eye and secure with a wooden or metal wedge driven in from the top.
Heat Treatment: Hardening and Tempering
Heat treatment is what transforms soft, malleable iron into a hard steel tool that holds a sharp edge. It only works on steel with sufficient carbon content (roughly 0.4% carbon or higher).
Hardening
Step 1 — Heat the tool to “critical temperature” — the point where the steel becomes non-magnetic. Test by touching a magnet to the steel between heats. When it stops attracting the magnet, you are at approximately 760-780 degrees C. The steel will be bright cherry red.
Step 2 — Quench immediately. For most carbon steels:
- Water quench: Fastest cooling, hardest result, but highest risk of cracking. Plunge the blade edge-first into the water, moving it in a figure-eight motion. Good for low-to-medium carbon steel (1040-1060).
- Oil quench: Slower cooling, less hard, less risk of cracking. Better for high-carbon steel (1075-1095). Use vegetable oil, motor oil, or rendered animal fat heated to about 50-60 degrees C. WARNING: oil may catch fire — have a metal lid ready to smother flames.
Step 3 — The steel is now at maximum hardness — and maximum brittleness. A fully hardened knife blade will shatter if dropped. You MUST temper it.
Tempering
Tempering sacrifices some hardness to gain toughness. You reheat the hardened steel to a specific temperature and let it cool.
Step 1 — Clean/polish the surface of the hardened steel so you can see color changes. Use a file, sandpaper, or abrasive stone to expose bright metal.
Step 2 — Gently heat the tool — NOT in the forge fire directly. Place it on a flat piece of steel that sits over coals, or heat the tang/spine and let the heat creep toward the edge. You need precise, even heat.
Step 3 — Watch for oxide colors to appear on the polished surface:
| Color | Temperature | Hardness | Best For |
|---|---|---|---|
| Pale straw | 220 degrees C | Very hard | Razor blades, scalpels, engraving tools |
| Dark straw | 240 degrees C | Hard | Knives, chisels, plane blades |
| Brown | 260 degrees C | Medium-hard | Axes, scissors, punches |
| Purple | 280 degrees C | Medium | Springs, saw blades |
| Blue | 300 degrees C | Tough, flexible | Springs, screwdrivers |
Step 4 — When the desired color reaches the working edge, quench immediately in water to stop the process.
For a knife: let the straw color reach the edge, then quench. The spine will be at purple or blue — tougher and more flexible — while the edge is hard enough to hold sharpness.
Method 2: Scrap Metal Recycling
In a post-collapse environment, you may not have access to bar stock or identifiable steel sources. Here is how to work with random scrap.
Step 1 — Gather metal. Sort it by spark test (see above) into piles of low-carbon, medium-carbon, and high-carbon.
Step 2 — For large pieces too thick to forge as-is: heat to yellow and hot-cut into workable sizes using a chisel and hammer on the anvil edge.
Step 3 — For thin pieces or sheet metal: stack multiple pieces, heat to white welding heat (1200+ degrees C — the surface will appear almost sparkling), and forge-weld them together. Sprinkle borax (if available) or clean silica sand as a flux between the layers before welding — this dissolves the oxide scale and allows the layers to fuse. Strike firmly and quickly when at welding heat.
Step 4 — Forge-welded bundles of scrap can be drawn out, folded, and re-welded to produce more uniform steel. Each fold doubles the layers and evens out the carbon distribution.
Method 3: Basic Smelting from Ore (Bog Iron Bloomery)
Smelting iron from ore is the most difficult process in this article. Expect your first attempt to fail. This section covers the bloomery process — the oldest method of iron smelting, used for thousands of years before the blast furnace.
Finding Ore
Bog iron is the easiest iron ore to find and smelt. It forms in swamps, bogs, and along stream banks where iron-rich groundwater meets the surface. Look for:
- Reddish-orange or rusty deposits in stream beds
- Heavy, rust-colored rocks in boggy areas
- Reddish staining on rocks near springs
Magnetite sand — black sand that sticks to a magnet. Found in stream beds, beaches, and river banks. Run a magnet through sand to collect it.
Hematite — heavy, dark red to silver-gray rock that leaves a red streak when rubbed on a white surface.
Building a Bloomery Furnace
Step 1 — Build a cylindrical shaft about 30 cm interior diameter and 100-120 cm tall from clay mixed with sand (about 60% clay, 40% sand). Walls should be at least 8-10 cm thick. Let the clay dry for at least a week, then fire it slowly before first use to prevent cracking.
Step 2 — At the base, leave an opening (arch) about 15 cm wide and 15 cm tall. This is your tapping arch where you will remove the bloom. Opposite this, insert a tuyere pipe about 10-15 cm above the base, angled slightly downward.
Step 3 — Connect your bellows to the tuyere. You need a steady, strong blast for 6-10 hours. Multiple operators taking shifts are nearly essential.
The Smelt
Step 4 — Fill the furnace with charcoal and light it from the top. Let it burn down to pre-heat the furnace for about 30 minutes while running the bellows.
Step 5 — Begin adding alternating charges of crushed ore and charcoal through the top of the furnace. A typical charge ratio is 1 part ore to 1 part charcoal by volume. Each charge: about 1-2 kg of ore and 2-3 kg of charcoal.
Step 6 — Add a new charge every 15-20 minutes as the level in the furnace drops. Maintain a continuous bellows blast throughout. The temperature at the tuyere level needs to reach 1200-1350 degrees C.
Step 7 — Continue for 6-10 hours. Inside the furnace, the carbon monoxide from the burning charcoal chemically reduces the iron oxide ore to metallic iron. The iron particles weld together into a spongy mass called a “bloom,” which collects at the bottom of the furnace.
Step 8 — After the final charge has burned down, remove the tapping arch block. Use long tongs or a hooked iron rod to extract the bloom. It will be a rough, irregular mass of iron mixed with slag (glass-like waste). It will be white-hot.
Step 9 — Immediately place the bloom on a flat stone or anvil and hammer it vigorously. This is called “consolidating” — you are squeezing out the liquid slag trapped inside the spongy iron. Reheat in the forge and hammer repeatedly until the surface becomes smooth and metallic.
Step 10 — The resulting wrought iron is very low in carbon — soft and tough, but it will not hold a sharp edge. To make steel, you need to add carbon through a process called “case hardening” or “cementation”: pack the iron in charcoal dust inside a sealed clay vessel and heat in the forge at bright cherry red for several hours. Carbon from the charcoal diffuses into the surface of the iron.
Expected Results
A successful bloomery smelt from 10-15 kg of bog iron ore and 30-50 kg of charcoal produces roughly 2-5 kg of usable wrought iron. The process is extremely fuel-intensive. This is why Charcoal Production must come first.
Common Mistakes
| Mistake | Why It’s Dangerous | What to Do Instead |
|---|---|---|
| Hammering cold metal | Creates invisible internal cracks that cause the tool to snap under stress | Always work above cherry red heat; reheat frequently |
| Heating past yellow to white (except for welding) | Iron “burns” — carbon is destroyed, and the metal crumbles like sugar | Watch heat colors carefully; pull from the fire at orange |
| Quenching high-carbon steel in water | Thermal shock causes cracks, especially in thick sections | Use oil quench for high-carbon steel (1075+) |
| Skipping tempering after hardening | Maximum-hardness steel is glass-brittle — it shatters on impact | Always temper immediately after hardening |
| Wearing synthetic clothing | Nylon and polyester melt into skin from radiant heat or sparks | Wear natural fibers: cotton, wool, leather |
| Forge welding without flux | Oxide scale between layers prevents bonding | Use borax or clean silica sand as flux |
| Insufficient bellows blast during smelting | Temperature never reaches reduction zone (1200+ degrees C), ore does not reduce | Maintain constant, strong air blast; use multiple operators in shifts |
| Getting the anvil wet | Steam explosions when hot metal is placed on wet anvil surface | Keep the anvil dry; quench in a separate container |
What’s Next
Metalworking unlocks most of the advanced tiers:
- Basic Electrical Circuits — metal wire, connectors, and tools for electrical work
- Simple Machines — metal axles, gears, bearings, and fasteners
- Woodworking — metal chisels, planes, saws, and drill bits
- Glassmaking — metal tools for handling molten glass, metal frames for glass furnaces
Quick Reference Card
Metalworking — At a Glance
Forge essentials: Firepot + charcoal + bellows + anvil + hammer + tongs
Heat colors (work in shade to see them): Cherry red (750 degrees C) = forging starts. Orange (950 degrees C) = ideal. Yellow (1100 degrees C) = maximum. White (1200+ degrees C) = welding only.
Four operations: Draw out (longer), upset (thicker), bend (angle), punch (holes).
Heat treatment:
- Heat to non-magnetic (cherry red, ~770 degrees C)
- Quench in oil (high carbon) or water (low carbon)
- Temper: reheat to straw (220-240 degrees C) for cutting tools
Spark test for carbon: Long straight sparks = low carbon. Bushy branching sparks = high carbon.
Best scrap sources: Leaf springs, coil springs, files = high carbon (tools/blades). Railroad spikes, rebar = low carbon (hooks, handles).
Bloomery smelting: 10-15 kg ore + 30-50 kg charcoal = 2-5 kg wrought iron. Expect your first attempt to fail. That is normal.