Metal Preparation

Part of Wire Drawing

Preparing metal stock before drawing: cleaning, annealing, and pointing for optimal results.

Why This Matters

Wire drawing fails or succeeds based on what happens before the wire ever touches a die. A perfectly made draw plate will produce cracked, rough, broken wire if the metal stock is poorly prepared. Conversely, well-prepared stock can produce usable wire even through mediocre dies.

Metal preparation encompasses three critical processes: cleaning the surface of oxides and contaminants, annealing to establish the correct softness and grain structure, and shaping the rod to the right starting dimensions. Skipping any of these steps creates problems that compound through every subsequent drawing pass.

For a rebuilding civilization working with hand-forged iron or native copper, preparation is especially important because the starting material is inherently less uniform than modern industrial stock. Bloomery iron contains slag. Native copper may have inclusions. Recycled metals carry surface contamination. All of these must be addressed before drawing begins.

Cleaning and Descaling

Every metal that has been heated — whether during smelting, forging, or annealing — develops a layer of oxide on its surface. This oxide layer (scale) is harder than the parent metal and will destroy dies if drawn through them.

Types of Surface Contamination

Contaminant	Source	Removal Method
Iron oxide scale (black)	Forging, annealing	Mechanical + acid
Copper oxide (red/black)	Annealing copper	Acid pickle
Forge scale (thick, flaky)	Heavy forging	Mechanical first, then acid
Carbon/soot	Fire, charcoal contact	Scrubbing with sand and water
Oil/grease	Handling, prior lubrication	Hot water wash, lye solution
Rust (red iron oxide)	Moisture exposure during storage	Wire brush, acid soak
Slag inclusions (surface)	Bloomery iron	Grinding, chiseling, heavy forging

Mechanical Cleaning

The first step is always mechanical removal of loose scale and debris.

1. Flexing — bend the rod or wire back and forth in a smooth arc. The brittle oxide scale cracks and flakes away from the ductile metal underneath. Do this over a collection area — iron scale is useful as a pigment and flux ingredient.
2. Scrubbing — pull the rod through a clamp of leather or heavy fabric packed with fine sand. This abrades remaining scale without damaging the metal.
3. Wire brushing — if you already have some wire, bundle short stiff pieces into a brush and scrub the stock. Circular motions work better than linear ones.
4. Tumbling — for small pieces, place in a container with sand and water, then shake or roll vigorously. The abrasive action of the sand removes scale uniformly.

Do Not Skip Mechanical Cleaning

Acid pickling alone will not remove thick forge scale. The acid attacks exposed metal faster than it dissolves the oxide, leading to pitting under the scale while the scale itself remains. Always break the scale mechanically first, then pickle to clean the residue.

Chemical Cleaning (Pickling)

Acid soaking dissolves remaining oxide after mechanical cleaning has removed the bulk.

Vinegar (acetic acid, ~5%)

• Soak time: 4-12 hours for light scale, up to 24 hours for heavier deposits
• Advantages: widely available, gentle, low risk of over-pickling
• Disadvantages: slow

Sour beer or wine (lactic/acetic acid mix)

• Soak time: 2-8 hours
• Advantages: stronger than vinegar, readily available in brewing communities
• Disadvantages: variable strength

Citrus juice (citric acid)

• Soak time: 1-4 hours
• Advantages: faster than vinegar
• Disadvantages: seasonal availability, may leave sticky residue

Fermented urine (uric acid + ammonia)

• Soak time: 2-6 hours
• Historically used extensively for iron wire in medieval Europe
• Advantages: free, effective, always available
• Disadvantages: unpleasant to work with

Post-Pickle Procedure

1. Rinse immediately in clean water — residual acid continues attacking the metal and causes pitting.
2. Neutralize — brief dip in wood ash water (mild alkali) stops any remaining acid reaction.
3. Dry thoroughly — iron flash-rusts within minutes if left wet. Wipe down and place near a fire to dry. Copper is more forgiving but should still be dried.
4. Coat with lubricant immediately after drying to prevent re-oxidation before drawing.

Annealing for Drawing

Annealing — controlled heating and slow cooling — establishes the soft, ductile grain structure needed for wire drawing. The goal is to reverse any work hardening from forging or prior drawing passes and create a uniform, fine-grained microstructure.

Annealing Temperatures

Metal	Annealing Temperature	Visual Indicator	Cooling
Copper	400-600°C	Dull red in dark room	Quench in water (OK for copper)
Wrought iron	700-750°C	Cherry red	Slow cool in ash/sand
Brass	450-600°C	Dull red	Quench in water
Bronze	400-550°C	Below visible glow	Slow cool or quench

Iron Cooling

Never quench iron in water after annealing — this hardens it (the opposite of what you want). Always slow-cool iron in ash, sand, or still air. Copper is the exception: quenching copper actually keeps it soft.

Annealing Procedure

1. Coil loosely — wire or rod should be in open coils with space between loops for even heat distribution. Tight bundles will have hard centers and soft outsides.
2. Heat uniformly — place in a charcoal fire, brick-lined furnace, or covered pit fire. The entire mass must reach annealing temperature. Use visual color indicators — in a dim workspace, you can see the glow color accurately.
3. Hold at temperature — maintain for 10-15 minutes per kilogram of metal. Insufficient hold time means incomplete recrystallization — the wire will still be partially hard.
4. Cool appropriately — see temperature table above.
5. Inspect — properly annealed wire bends easily without cracking. Iron should bend 90 degrees and back without fracture. Copper should bend 180 degrees flat.

When to Anneal

Stage	Anneal?	Why
Before first draw (from forged rod)	Yes — always	Rod is work-hardened from forging
Between drawing passes (copper)	Every 4-5 passes	Copper work-hardens slowly
Between drawing passes (iron)	Every 2-3 passes	Iron work-hardens quickly
After final draw	Depends on application	Soft wire: anneal. Spring wire: do not anneal.

Rod Sizing and Shaping

The starting rod must be the right size and shape for efficient drawing. Too large wastes passes; too small limits your maximum wire length; too irregular causes uneven stress and cracking.

Determining Starting Rod Size

The starting rod should be no more than 3-4 die sizes larger than your target wire gauge. Each die size represents roughly 15-20% area reduction. Larger starting rods require more passes, more annealing, more fuel, and more time.

Target Wire	Recommended Starting Rod	Passes
4 mm	6-8 mm	4-6
2.5 mm	5-6 mm	6-8
1.5 mm	4-5 mm	8-12
1.0 mm	3-4 mm	10-14

Forging to Rod

For hand-forged rod stock, the critical requirements are:

1. Uniform cross-section — the rod should be the same thickness along its entire length. Thick spots create excess stress in the die; thin spots break.
2. Smooth surface — forge marks, hammer dimples, and surface folds all become crack-starting points during drawing. Finish-forge on a smooth, flat anvil face.
3. Straight — a badly bent rod enters the die at an angle, creating uneven stress. Straighten by rolling under a flat board on the anvil or pulling through a straightening block (a block of wood with a hole slightly larger than the rod).
4. Consistent metallurgy — the rod should have uniform carbon content and slag distribution throughout. This comes from thorough folding and welding during bloom processing.

Round vs. Square Rod

Shape	Advantages	Disadvantages
Round	Enters die evenly, less stress concentration	Harder to forge accurately
Square	Easier to forge, good grip for tongs	First 2-3 passes round the corners unevenly
Octagonal	Compromise — easier to forge than round, rounder than square	Requires swage or grooved anvil

For most practical purposes, square rod works fine for the first few passes. By the third or fourth die, the wire is effectively round regardless of starting shape.

Straightening

Bent or curved rod stock must be straightened before drawing. An off-center wire entering the die experiences uneven compression — one side is reduced more than the other — leading to curved exit wire and eventual cracking.

Straightening Methods

1. Rolling — place the rod on a flat surface and roll a heavy flat object (board, iron bar) back and forth across it. Effective for gentle curves in smaller stock.
2. Drawing through a straightening block — drill a hole slightly larger than the rod in a hardwood block. Pull the rod through several times, rotating between pulls. The block forces the rod straight.
3. Hammer straightening — place the rod on an anvil with the bend facing up. Tap lightly at the apex of the bend. Work carefully — over-hammering introduces new bends and work-hardens the rod.
4. Tension straightening — anchor one end and pull the other end firmly. This only works for mild curves and soft metals.

Inspection Before Drawing

Before committing a prepared rod to the draw plate, conduct a final inspection.

Checklist

• Surface is clean — no visible scale, rust, or contamination
• Surface is smooth — no forge marks, seams, or cracks detectable by touch
• Rod is straight — rolls smoothly on a flat surface without wobbling
• Rod is uniformly sized — check diameter at multiple points with calipers or a gauge plate
• Rod is properly annealed — bends easily without cracking
• Rod is dry — no residual moisture from pickling
• Rod is lubricated — thin, even coating of tallow, wax, or soap
• Pointed end is properly tapered — smooth taper, correct length, no cracks at the shoulder

The Five-Minute Rule

Five minutes spent inspecting and preparing a rod saves an hour of dealing with broken wire, damaged dies, and wasted material. Never rush preparation to start drawing sooner.

Preparing Recycled and Salvaged Metal

In a rebuilding scenario, much of your wire stock may come from salvaged materials rather than freshly smelted metal.

Common Salvage Sources

Source	Metal	Preparation Needed
Electrical wiring	Copper	Strip insulation, clean, anneal
Nails and screws	Mild steel	Straighten, remove coatings, anneal
Fence wire	Galvanized iron	Remove zinc coating (heat to burn off), anneal
Automotive springs	High-carbon steel	Anneal thoroughly — very hard as-found
Plumbing pipe	Copper or brass	Flatten, cut to strips, forge to rod
Rebar	Mild steel	Cut to length, forge to rod, anneal

Key Considerations for Salvaged Metal

• Unknown composition — salvaged metal may be an alloy you cannot identify. Test by drawing a short sample before committing to a full batch.
• Coatings — galvanized (zinc-coated), chrome-plated, or painted metals must be fully stripped before drawing. Zinc in particular is toxic when heated and will contaminate dies.
• Work history — salvaged wire that was previously drawn may be fully work-hardened. Always anneal salvaged stock regardless of apparent softness.
• Mixed metals — never draw mixed metals through the same die without cleaning between batches. Copper residue on an iron die (or vice versa) causes adhesion and galling.