A technical refining reference from Aurora Gold & Silver covering common jewelry alloy systems, melt behavior, oxidation mass, vaporization risk, and practical melt-loss expectations for karat gold scrap.
In commercial jewelry alloys, the most common non-gold metals are silver, copper, nickel, and zinc. These metals account for the majority of standard karat gold alloys. Cadmium may appear in older jewelry and legacy solders, while palladium and platinum are used in higher-grade white gold alloys.
| Alloy Type | Typical Composition | Refining Relevance |
|---|---|---|
| Yellow Gold | Gold, silver, copper, sometimes zinc | Moderate oxidation from copper; lower zinc risk than white gold |
| Rose / Red Gold | Gold and copper, with silver as balance | Higher copper means more oxide scale and slag contribution |
| Nickel White Gold | Gold, nickel, zinc, copper | High zinc content makes this a major vapor-loss category |
| Palladium White Gold | Gold and palladium, often with silver | Higher melting behavior; palladium oxidation/discoloration requires care |
| Green Gold / Electrum | Gold and silver | Usually lower oxide risk unless contaminated with old solder or cadmium |
| Metal | Melting Point | Boiling Point | Behavior During Karat Gold Melting |
|---|---|---|---|
| Gold | 1,064°C | 2,856°C | Does not oxidize in air, but its volatility increases in the presence of metallic impurities. |
| Silver | 962°C | 2,162°C | Does not form a stable oxide at melt temperature; dissolves oxygen and may spit on solidification. |
| Copper | 1,084°C | 2,562°C | Oxidizes readily and is the dominant oxide source in karat gold scale. |
| Zinc | 419.5°C | 907°C | Actively volatilizes at karat gold melt temperatures and forms zinc oxide fume. |
| Nickel | 1,455°C | 2,913°C | Oxidizes to nickel oxide but does not vaporize meaningfully at karat melt temperatures. |
| Palladium | 1,555°C | 2,973°C | Can oxidize/discolor above roughly 400°C; controlled or inert heating is preferred. |
| Platinum | 1,768°C | 3,825°C | Effectively inert to oxidation at jewelry-relevant temperatures. |
| Cadmium | 321°C | 767°C | Volatilizes early and produces acutely toxic cadmium oxide fume. |
Yes. Oxides weigh more than the starting metal because oxygen from the atmosphere becomes chemically bound to the metal. For example, copper gains mass when it forms copper oxide because oxygen is added to the reaction product.
| Scenario | What Happens | Refining Impact |
|---|---|---|
| Oxide stays in slag or melt | Copper oxide, nickel oxide, or palladium oxide reports into the flux layer and is left behind in the crucible | Potentially recoverable through reduction or chemical processing |
| Oxide volatilizes | Zinc or cadmium leaves as oxide fume | True mass loss through the hood or exhaust system |
| Gas dissolves without stable oxidation | Silver dissolves oxygen and releases it on cooling | Causes porosity or spitting, but not a true refiner loss |
These are the dominant real-world vapor-loss metals in karat scrap.
Zinc and cadmium are the major practical concerns because their boiling points fall below or near common karat gold melting temperatures. Zinc is especially important in white gold alloys and solder-bearing scrap.
For clean, segregated karat gold scrap melted with proper flux, minimum effective temperature, and clean pouring practice, a competent refiner should generally expect 0.5% to 2.0% total lot weight loss.
| Lot Size | Expected Loss | Absolute Loss | Operational Notes |
|---|---|---|---|
| 50 grams | 1% to 3% | 0.5 g to 1.5 g | Surface effects dominate; crucible wetting, flux retention, and pour technique matter more. |
| 100 grams | 0.75% to 2% | 0.75 g to 2 g | Efficient torch melt size; suitable for representative assay bar. |
| 250 grams | 0.5% to 1.5% | 1.25 g to 3.75 g | Strong size range for torch or small induction melts. |
| 500 grams to 1 kilogram | 0.3% to 1.2% | 1.5 g to 12 g | Induction melting preferred; composition dominates loss. |
| 2 kilograms and above | 0.2% to 1% | Variable | Commercial refiner scale; controlled atmosphere can reduce loss further. |
Zinc is the most important ordinary alloying metal for melt-loss prediction. A 10K or 14K white gold lot with 6% to 8% zinc can lose substantially more weight than a low-zinc yellow gold lot.
Karat gold melts are not typically skimmed; instead, the melt is protected under flux, poured cleanly, and oxide-rich flux is left behind.
On a typical mixed karat gold scrap lot, Aurora Gold & Silver expects approximately 1% to 2% melt loss under normal shop conditions. Clean yellow gold may perform better, while white gold, zinc-bearing scrap, old solder, and legacy cadmium-bearing material may produce wider losses.
Melt loss is not random. It is driven by alloy composition, oxidation, vaporization, flux practice, temperature control, and operator discipline. Over time, measuring every melt creates a practical yield database that improves pricing, accountability, and refining accuracy.