Because of the softness of pure (24k) gold, it is usually alloyed with base metals for use in jewellery, altering its hardness and ductility, melting point, colour and other properties. Alloys with lower caratage, typically 22k, 18k, 14k or 10k, contain higher percentages of copper, or other base metals or silver or palladium in the alloy. Copper is the most commonly used base metal, yielding a redder color.
Silver jewellery is traditionally made from sterling silver, an alloy of 92.5% silver with 7.5% copper. Sterling silver is harder than pure silver and is usually stamped 925.
Platinum's resistance to wear and tarnish is well suited for making fine jewellery. Platinum in jewellery is usually as a 90–95% alloy. Watchmakers appreciate the unique properties of platinum, as it neither tarnishes nor wears out (relative to gold). Because only a few hundred tonnes are produced annually, it is a scarce material, and is highly valuable and is a major precious metal commodity.
Because of its durability, titanium has become more popular for designer jewellery (particularly, titanium rings). Its inertness makes it a good choice for those with allergies or those who will be wearing the jewellery in environments such as swimming pools.
Titanium is also alloyed with gold to produce an alloy that can be marketed as 24-carat gold, as the 1% of alloyed Ti is insufficient to require a lesser mark. The resulting alloy is roughly the hardness of 14-carat gold and thus is more durable than a pure 24-carat gold item would be.
Titanium's durability, light weight, dent- and corrosion resistance makes it useful in the production of watch cases.