Doublet / Gold Doublet
Also: Doublet, Gold-Filled, Rolled Gold, Doublé
Gold doublet is a base-metal core (usually brass or copper) mechanically bonded to a thick layer of gold by hot rolling — in contrast to electrolytic gold plating.
Gold doublet (also doublé, English Gold Filled or Rolled Gold) denotes a composite material in which a comparatively thick layer of gold is permanently bonded, by mechanical hot rolling or pressing, to a base carrier material — usually brass, copper or nickel silver. The result is visually almost indistinguishable from solid gold but contains only a fraction of the gold value.
Manufacture and structure
In the doublet process, a gold sheet (usually a 333 to 750 alloy) is rolled together with the base metal at high temperature until both layers form an inseparable metallic bond. The gold layer makes up at least 1/20 of the total weight (the American Gold Filled standard) and, at 20–100 micrometres, is considerably thicker than an electrolytic gold plating (0.1–5 µm). This layer thickness gives gold doublet considerably better wear resistance.
Distinction: doublet, plating, doublé
| Feature | Gold doublet | Electrolytic gold plating | Solid gold |
|---|---|---|---|
| Bond | Mechanical (rolling) | Electrolytic | Monolithic |
| Layer thickness | 20–100 µm | 0.1–5 µm | Solid material |
| Gold share of weight | approx. 5% | < 0.1% | 100% |
| Durability | High (years to decades) | Low to medium | Permanent |
| Total fineness | Below 333 ‰ | Below 333 ‰ | Depending on alloy |
Important: Because the fineness of the whole piece is generally below 333 per mille, gold doublet is not considered a precious metal in the legal sense and may not be stamped with a hallmark for genuine gold.
Marking and legal position
Gold doublet must be clearly marked as such — typical markings are GF (Gold Filled), RG (Rolled Gold), Doublé or a designation such as 20/1000 GF 14K. A misleading designation as "gold" or a genuine gold hallmark is prohibited. In the USA, the FTC Jewelry Guides govern the minimum requirements for Gold Filled jewellery.
You can estimate the actual material value with the Melt Value Calculator — although with doublet pieces only the weight of the gold layer is relevant, not the total weight. Whether a piece is really doublet or solid gold is revealed by authenticity testing or a professional streak/acid test at the jeweller.
Formulas for the gold content
Gold weight = Total weight × (Layer share / 1000) × (Fineness-carat / 24)
Example: 10 g bracelet, 1/20 GF, 14K → 10 × 0.05 × 0.583 ≈ 0.29 g fine gold
In brief
Gold doublet offers the visual sheen of gold at a fraction of the price but has no significant material value as a precious metal. For buying and melting, the actual fine gold content is decisive — this can be determined with the Purchase Price Calculator once the layer parameters are known.