How to melt gold in a workshop

At a glanceMelting gold in a jewelry workshop is a core craftsmanship skill required to turn scrap, sprues, and bench filings back into workable ingots for rolling or wire drawing. This operation demands precise temperature management, proper equipment, and strict adherence to workplace safety regulations established by SUVA in Switzerland. Here is the complete step-by-step foundry guide.

1. Essential Foundry Equipment Checklist

To safely melt batches from 20 to 500 grams of gold in a jeweler's workshop:

• The crucible: High-density graphite or clay-graphite crucible with a pouring spout. Graphite creates a naturally reducing carbon monoxide atmosphere during heating.
• Heat source: Jeweler's torch (oxy-propane) with a multi-orifice rosebud heating tip, or a digital electric melting furnace (rated up to 1,150 °C).
• Crucible tongs: Forged tongs tailored to clamp the crucible securely and prevent tipping during the pour.
• Ingot mold (Lingotière): Heavy-duty cast iron or machined steel reversible mold for pouring flat sheet ingots or square wire rods.
• Fluxing agents: Anhydrous borax powder (sodium tetraborate) and boric acid for oxidation protection and slag fluidization.
• Stirring rod: High-purity graphite rod or quartz rod to homogenize molten alloys.

2. Step-by-Step Operating Protocol

Step A: Preparing and Glazing the Crucible

Heat a new crucible to a dull red glow and dust the interior with borax powder. The borax melts into a glossy protective glaze that coats the graphite, preventing molten gold from penetrating the pores.

Step B: Preheating the Ingot Mold (Vital Safety Step!)

Always preheat the cast iron ingot mold to 150–200 °C. Pouring molten gold (over 1,000 °C) into a cold, damp mold will cause instant steam explosions that violently eject molten metal across the room. Lightly lubricate the mold cavity with beeswax or mineral oil.

Step C: Heating and Melting

1. Place larger scrap pieces at the bottom of the crucible, topped with finer clippings.

2. Ignite the torch with a soft, slightly reducing flame (neutral blue cone).

3. Circle the flame evenly around the crucible to heat the mass uniformly.

4. As the gold slumps and begins to liquefy, add a pinch of borax.

5. Once fully liquid, the surface forms a shimmering mirror pool. Stir gently with a preheated graphite rod for 15 seconds.

Step D: The Pour

Bring the crucible and torch together to the mold. Keep the flame centered on the crucible spout during the entire pour to prevent skin freezing. Pour in a single, smooth, decisive motion.

Step E: Quenching and Pickling

Allow the ingot to solidify for 30 seconds, quench in water, and submerge in a warm pickling bath (10% sodium bisulfate / sparex) for 5 to 10 minutes to dissolve glassy borax residue and copper oxides.

3. SUVA Safety Standards in Swiss Workshops

• Eye protection: Safety glasses with infrared/UV filters (shade DIN 4 or 5) to prevent thermal eye damage.
• Thermal protection: Long split-leather welder's gloves and leather apron.
• Fume extraction: Never melt in a closed space without dedicated point-source local exhaust ventilation. Fumes of zinc, cadmium, and lead from antique jewelry are highly neurotoxic.

Frequently Asked Questions (FAQ): Workshop Melting

Can jewelry with set gemstones be melted directly?

No. All stones must be unmounted prior to melting. Even diamonds can burn and cloud in a torch flame above 800 °C.

Why does my ingot have cracks along the edges during rolling?

Edge cracking during rolling typically indicates pouring into an insufficiently preheated mold, or contamination with tin/lead from soft solders.