Additive / Alloying Metal
Also: Additive metal, Base addition, Alloying agent
An alloying metal is a base or precious metal added to a precious metal in a defined quantity to deliberately alter hardness, colour, melting behaviour or other properties.
An alloying metal (also additive metal or alloying agent) is the portion of a precious metal alloy that does not consist of the precious metal itself. Without alloying metals many applications would scarcely be possible: pure gold (999.9 ‰) is so soft that it can be scratched with a fingernail - only the addition of other metals gives jewellery or a coin the necessary working hardness. The fineness always indicates how much precious metal - and thus how little alloying metal - is contained in an alloy.
Which metals are used?
| Alloying metal | Typical use | Effect |
|---|---|---|
| Copper | Red gold, sterling silver, 585 gold | Hardness ↑, red colouring |
| Silver | Yellow gold, white gold base alloys | Lighter colour, ductility |
| Palladium | White gold (hypoallergenic) | White colouring, tarnishing ↓ |
| Nickel | Older white gold | White colouring (allergy potential) |
| Zinc | Solder alloys, yellow gold | Melting point ↓, hardening |
| Iridium / Ruthenium | Platinum alloys | Hardness ↑ in platinum |
Influence on the material value
The melt value of a piece of jewellery is based solely on the fine weight of the precious metal, not on the weight of the alloying metals. In a 585 gold ring with a gross weight of 10 g, only 5.85 g of fine gold is value-relevant - the remaining 4.15 g of alloying metal (often copper and silver) barely enters the valuation. You can determine the exact material value with the melt value calculator.
Fine weight = gross weight x (fineness ÷ 1000)
Example 585 gold, 10 g: 10 x 0.585 = 5.85 g fine gold
Colour effect through alloying metals
The colour of a gold alloy depends directly on the mixing ratio of the alloying metals:
- Red gold / rose gold: high copper content (e.g. 750 ‰ gold + ~200 ‰ copper + ~50 ‰ silver)
- White gold: palladium (hypoallergenic) or historically nickel replaces copper entirely
- Green gold (electrum): high silver content, little or no copper
Tarnishing and allergy risk
Copper and nickel as alloying metals can trigger contact allergies in sensitive wearers. Nickel is strictly regulated in the UK and the EU for jewellery, body piercing jewellery and skin-contact articles - the original Nickel Directive 94/27/EC was replaced by REACH Regulation (EC) No 1907/2006, Annex XVII entry 27, and further tightened (retained in UK law under UK REACH). Palladium is regarded as a more tolerable alternative. Silver develops a dark tarnish layer through sulphur compounds in the air - the alloying metal copper accelerates this process.
In brief
The alloying metal determines the colour, hardness, allergy risk and tarnishing behaviour of a precious metal alloy, but has no significant influence on the precious metal value - what matters is solely the fineness of the precious metal.