Alloy
Also: Metal Alloy, Alloying Metal
An alloy is a mixture of a base metal and one or more additive metals (alloying metals) that has deliberately altered physical or chemical properties.
An alloy is created when at least two metallic elements are melted together. In the precious metals field, the base metal – gold, silver, platinum or palladium – is always the main constituent; the additive metals determine colour, hardness, workability and corrosion resistance. The fineness indicates what proportion of the total weight is accounted for by the pure precious metal – expressed in thousandths (per mille) or carats.
Why is precious metal alloyed?
Pure gold (999.9 ‰) is very soft and barely suitable for jewellery. Alloying makes it possible to:
- Increase hardness and abrasion resistance (important for rings and bracelets)
- Deliberately control colour – copper produces red gold, palladium or nickel produces white gold
- Adjust the melting point (relevant for processing in the foundry)
- Reduce cost – a lower precious metal content reduces the material value
Typical gold alloys at a glance
| Designation | Fineness | Carat | Typical additive metals |
|---|---|---|---|
| Fine gold | 999 ‰ | 24 kt | – |
| 916 gold | 916 ‰ | 22 kt | Copper |
| 750 gold | 750 ‰ | 18 kt | Cu, Ag, Pd, Ni |
| 585 gold | 585 ‰ | 14 kt | Cu, Ag, Zn |
| 375 gold | 375 ‰ | 9 kt | Cu, Ag, Zn |
| 333 gold | 333 ‰ | 8 kt | Cu, Ag, Zn |
Silver alloys
Silver too is almost always alloyed. The best-known example is sterling silver with 925 ‰ silver and 75 ‰ copper – a standard that has applied to coins and cutlery since the Middle Ages. Other common finenesses:
- 835 silver – classic cutlery silver in continental Europe
- 800 silver – common in older coin and table silver
- 958 silver (Britannia) – high-purity silver, especially for British coins
Calculating the material value
The melt value of an alloy results from the fine weight:
Fine weight = gross weight × (fineness ÷ 1000)
Melt value = fine weight × current spot price per gram
With the melt value calculator this value can be quickly determined for gold, silver and other metals. The gold calculator automatically takes the entered fineness into account.
White gold – a special group
White gold is a gold alloy that acquires a silvery colour through the addition of palladium or nickel. Because the yellow tone often still shows through, white gold pieces are frequently rhodium-plated – coated with a thin layer of rhodium that provides the characteristic high gloss. This layer wears off and must occasionally be renewed.
Recognising and testing alloys
The fineness hallmark (punch mark) on jewellery provides information about the composition. In Malta and the EU, the statement in thousandths is customary (e.g. "585" for 14-carat gold). X-ray fluorescence analysis (XRF) enables a non-destructive, precise determination of the alloy composition – important when buying scrap gold.
In brief
Alloys are what make precious metals practical: they control colour, hardness and workability, while the fineness definitively sets the true precious metal content – and thus the intrinsic value. When buying or selling jewellery and bars, it always pays to check the hallmark and per mille figure.