Gold alloys
18k Yellow Gold
18 karats, 750‰
Classic warm yellow, the industry standard for fine jewellery worldwide; richer and deeper than 14k
Composition
75% gold, typically 12.5% silver, 12.5% copper; the classic three-component yellow alloy
Physical properties
| Density | 15.50 g/cm³ | Weight per unit volume. Platinum is ~40% heavier than 18k gold at equal size |
|---|---|---|
| Melting range | 880–1010 °C | Working temperature for alloys. Pure metals have a sharp melting point |
| Vickers hardness | 125 HV | Higher HV = greater scratch resistance in service |
| Mohs hardness | 3 | Approximate equivalent for comparative reference |
| Tensile strength | 490 MPa | Resistance to breaking under tension, relevant for prongs and fine settings |
| Purity | 75.00% | Fine metal content by mass |
| Tarnish resistance | Excellent | Surface oxidation / sulphidation under typical wear conditions |
| Workability | Excellent | Ease of forming, soldering, and fabricating under standard jewellery workshop conditions |
| Hypoallergenic | Hypoallergenic | Likelihood of triggering skin reactions under normal wear |
Common uses
Fine jewellery of all types, engagement and wedding rings, high-end watches, gemstone settings, heirlooms
Hallmarking & identification
Stamped 750 in most countries; 18K or 18ct in Anglo-American markets. European standard for premium jewellery.
Care & maintenance
Very stable; clean with warm soapy water and a soft brush. Avoid chlorine and bleach. Store in a fabric-lined box.
Market & pricing
75% of gold spot plus alloy and fabrication premium. Dominant fine jewellery standard in Europe, Asia, and the Middle East.