Smelt Copper Prills (Small Batch)

Summary

This article describes a practical first smelt: producing small metallic copper droplets (“prills”) from ore. You then recover and consolidate these prills into a workable metal piece.

Prerequisites

• Charcoal fuel: Make Charcoal Fuel (Pit Method)
• Furnace: Build a Small Clay Furnace (With Tuyere)
• Ore selection: Find and Test Copper Ore (Field Method)

Materials

• Tested copper ore (crushed)
• Charcoal (lump + fine)
• Small amount of silica-rich sand or ash (optional flux)
• Clay furnace with working tuyere
• Hammerstone and flat stone for breaking slag and recovering prills

Steps

1) Prepare ore

1. Crush ore to coarse sand / small grit.
2. Remove obvious waste rock and dirt.
3. Optional: roast ore in an open charcoal fire until dry and brittle.

Roasting often improves reduction behavior and makes ore easier to crush.

2) Heat furnace to operating temperature

1. Fill lower furnace with charcoal.
2. Start fire and build a bright hot zone near tuyere level.
3. Run airflow until charcoal bed is fully established.

3) Charge ore and charcoal in layers

1. Add a thin ore layer.
2. Cover with charcoal.
3. Repeat small layers, keeping top mostly charcoal.

Do not smother the furnace with too much ore at once.

4) Maintain hot reducing conditions

1. Keep strong heat and steady airflow.
2. Refill charcoal as it drops.
3. Continue 1 to 3 hours depending on furnace size and charge amount.

You want sustained bright heat, not intermittent flare-ups.

5) Recover prills

1. Let furnace cool to safe handling temperature.
2. Remove slaggy masses from the reaction zone.
3. Break slag on a flat stone.
4. Pick out metallic copper prills/droplets.

Repeat batches to accumulate enough copper for a tool blank.

Verification

• Prills are metallic copper color (often reddish to orange-brown after cleaning).
• Prills flatten under hammering instead of shattering.
• Collected prills can be consolidated by reheating and hammering.

Safety

• Smelting fumes can be hazardous. Work outdoors, upwind, and avoid inhaling smoke/dust.
• Never add wet ore/charcoal into very hot furnace zones; steam and spall can eject hot material.
• Heat-retaining slag stays dangerous for a long time.

Troubleshooting

• No metal recovered: ore may be low grade, furnace too cool, or atmosphere too oxidizing.
• Prills are very tiny and scarce: crush ore finer, run longer, use stronger airflow.
• Too much glassy slag: reduce flux/additives, adjust ore-to-charcoal ratio, avoid overfeeding gangue-rich ore.

Variants

• Multiple re-smelts: re-smelt slag and low-grade residues to recover additional copper.
• Bowl furnace method: lower throughput but simpler construction.