Platinum melting: technical challenges

Platinum melts at 1,768°C — which is 700°C more than gold and 800°C more than silver. This melting point requires entirely dedicated workshop equipment, much more expensive than for gold.

Equipment required: High-frequency induction furnace (recommended), or ~3000°C oxy-hydrogen torch (acceptable). Zirconia or magnesite crucible (graphite crucibles react with platinum at high temperature and contaminate it). Titanium or high-temperature stainless steel tongs.

Flux: Platinum is melted under vacuum or inert atmosphere (argon) to avoid absorption of oxygen and nitrogen. 'Galvanized' platinum by gases becomes porous on solidification — micro-bubbles make the piece brittle.

Jewelry Alloys: Pure platinum (999) is too soft for jewelry. It is alloyed with 5% iridium (hardener, Pt950Ir), 5% ruthenium (even harder, Pt950Ru) or 5% cobalt (Pt950Co, slightly magnetizable). Cobalt was abandoned in wedding bands due to rare skin reactions.

Melting Loss: Very low for platinum (<0.5%) under induction furnace conditions under argon. The main loss is due to casting splatter. Use an ingot mold pre-heated to 200°C to avoid thermal shock and superficial porosity.