Alloy
Also: Metal alloy, Alloying metal
An alloy is a mixture of a main metal and one or more additive metals (alloying metals), created deliberately to give it altered physical or chemical properties.
An alloy is created when at least two metallic elements are fused together. In the precious metals field the base metal - gold, silver, platinum or palladium - is always the main component; the additive metals determine colour, hardness, workability and corrosion resistance. The fineness indicates what proportion of the total weight is pure precious metal - expressed in thousandths (per mille) or carats.
Why is precious metal alloyed?
Pure gold (999.9 ‰) is very soft and hardly suitable for jewellery. Alloying allows one to:
- Increase hardness and abrasion resistance (important for rings and bracelets)
- Control colour deliberately - copper produces red gold, palladium or nickel produces white gold
- Adjust the melting point (relevant for foundry processing)
- Reduce cost - a lower precious metal content reduces the material value
Typical gold alloys at a glance
| Designation | Fineness | Carats | Typical additive metals |
|---|---|---|---|
| Fine gold | 999 ‰ | 24 ct | - |
| 916 gold | 916 ‰ | 22 ct | Copper |
| 750 gold | 750 ‰ | 18 ct | Cu, Ag, Pd, Ni |
| 585 gold | 585 ‰ | 14 ct | Cu, Ag, Zn |
| 375 gold | 375 ‰ | 9 ct | Cu, Ag, Zn |
| 333 gold | 333 ‰ | 8 ct | Cu, Ag, Zn |
Note that 9 carat (375) is the most common jewellery standard in the United Kingdom, alongside 18 carat (750).
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 widely used finenesses:
- 835 silver - traditional continental cutlery silver
- 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 is derived from the fine weight:
Fine weight = gross weight x (fineness ÷ 1000)
Melt value = fine weight x 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 gives the characteristic high gloss. This layer wears off and must be renewed occasionally.
Identifying and testing alloys
The fineness stamp (hallmark) on jewellery gives information about the composition. In the UK, hallmarking by an assay office is legally required for precious metal articles above certain weight thresholds. 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 fixes 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.