Gold alloys by color: yellow, white, rose, green
Chemical composition and properties of each gold color used in jewelry.
At a glanceIn Swiss horology and fine jewelry, pure 24-karat gold (999‰) is prized for its rich sun-yellow luster, but its excessive softness makes it unsuitable for water-resistant watch cases or rings subjected to daily wear. By alloying gold with silver, copper, palladium, or platinum, metallurgists enhance hardness, elasticity, and generate distinct color nuances. This guide explores the metallurgy of 18-karat (750‰) gold colors.
The Ternary Au-Ag-Cu Phase Diagram
Under the Swiss Precious Metals Control Act (LCMP), 18-karat gold must contain exactly 75.0% pure gold by weight. The remaining 25.0% (the master alloy) determines both color and mechanical properties:
- Silver: Bleaches gold toward pale yellow and greenish-yellow, preserving ductility.
- Copper: Imparts a warm reddish tone and increases hardness through lattice distortion.
- Palladium: Powerfully decolors gold to a noble white without triggering allergic skin reactions.
Standardized Formulations for 1,000 g of 18k Gold (NIHS 03-01 Standard)
The following table details recipes to formulate 1,000 grams of 18k gold according to Swiss watch industry standards:
| Standard Designation | Color Shade | Fine Gold 999 (g) | Fine Silver (g) | Electrolytic Copper (g) | Fine Palladium (g) | Annealed Hardness (HV) | Work-Hardened (HV) |
|---|---|---|---|---|---|---|---|
| Yellow Gold 2N | Light Swiss yellow | 750 g | 160 g | 90 g | 0 g | 120 HV | 200 HV |
| Yellow Gold 3N | Classic rich yellow | 750 g | 125 g | 125 g | 0 g | 130 HV | 210 HV |
| Rose Gold 4N | Delicate balanced rose | 750 g | 90 g | 160 g | 0 g | 150 HV | 230 HV |
| Red Gold 5N (Watchmaking) | Deep intense red | 750 g | 45 g | 205 g | 0 g | 160 HV | 250 HV |
| White Gold (13% Pd) | Natural silvery white | 750 g | 50 g | 70 g | 130 g | 150 HV | 240 HV |
| Green Gold (Electrum) | Soft pale greenish | 750 g | 250 g | 0 g | 0 g | 100 HV | 180 HV |
Why Swiss Luxury Demands Palladium White Gold
Historically, commercial white gold was bleached using nickel (inexpensive and hard). In Switzerland and the EU, the REACH Regulation / Nickel Directive (EN 1811) strictly bans jewelry with high nickel release rates due to contact allergies (dermatitis).
Swiss haute horlogerie and bijouterie now exclusively formulate Palladium White Gold:
- 100% hypoallergenic and biocompatible.
- Permanent color: Unlike nickel white gold that yellows noticeably when surface rhodium plating wears off, palladium white gold is gray-white throughout its molecular body and never turns yellowish.
Heat Treatment and Age Hardening of 5N Red Gold
Copper-rich 5N red gold exhibits an interesting metallurgical property: age-hardening via order-disorder transformations. Heating to 400 °C for 30 minutes followed by slow cooling prompts precipitation of the ordered AuCu phase, driving hardness over 280 HV—rivaling premium stainless steel watch cases.
Frequently Asked Questions (FAQ): Gold Alloys
Do real black or blue golds exist?
Black gold is a surface electroplating (ruthenium) or PVD carbon coating, not a solid bulk alloy. Blue gold is a brittle intermetallic compound ($AuIn_2$ with indium), useful only for ceramic-like inlays.
Does rose gold have the same scrap value as yellow gold?
Yes, exactly the same value per gram of fine gold. Both contain exactly 750‰ pure gold.
Buy Investment Gold in Switzerland (VAT-Exempt)
Buy and store physical gold in secure Zurich or Geneva vaults at direct live LBMA spot rates.
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