- Melting temperature: °C 960.5
Pure silver or fine silver is too soft to be made into a piece of jewellery. The silver is alloyed with other metal—usually copper—in order to improve its hardness and durability. Sterling silver is the most popular alloy, comprising 92.5% pure silver and 7.5% copper. Sterling silver will be hallmarked with a ‘925’ mark, which stands for 92.5% pure silver.
Sterling silver is a relatively affordable material, but the price of a silver item will depend on the labour involved, the design, and the skills of the craftsperson.
The only inconvenience is that silver oxidises (tarnishes) when exposed to oxygen in the air, subsequently causing the surface to turn black; Therefore, IT has to be cleaned on a regular basis.
- Melting temperature: °C 1,063.0
Like silver, gold is soft and so, in order to vary its colour and hardness, gold is alloyed to other metals. Native gold is yellow, but alloyed to silver, platinum or zinc will turn its colour white. Copper is added in order to obtain a red or pink gold, and iron for a tinge of blue.
The purity of the gold is indicated in terms of its carat, which defines the proportion of pure gold present in the metal. Pure gold is 24 carat; therefore, the purity of the gold is expressed in 24ths, meaning 18ct gold is an alloy of 18 parts pure gold and 6 parts other metals. The purity of gold used in jewellery are 9ct, 14ct, 18ct, 22ct and 24ct, the latter of which is rarely used in jewellery as it is too soft. The hallmark will represent the fineness of the metal in parts per thousand: 9ct gold will be marked ‘375’, 14ct ‘585’, 18ct ‘750’, 22ct ‘916’ and 24ct ‘999’.
The price of gold will depend mainly on the purity of the metal as well as the labour and design of the piece.
White gold contains native yellow gold alloyed with other metals to obtain a white metal with a slight yellow colour. Almost all white gold is plated to enhance the whiteness. Over time, the rhodium plating may wear off, and so white gold rhodium re-plating is needed in order to maintain the whiteness of the metal.
- Melting temperature: °C 1,773.5
Platinum is the rarest of the three precious metals—30 times rarer than gold. Platinum is also most durable, more resistant to corrosion, and does not tarnish (unlike silver). It is slightly more dense than pure gold, and approximately twice as dense as silver. Like silver and gold, platinum is alloyed with other metals, and is usually 95% platinum with 5% other metal. Pure platinum is hallmarked ‘999’, and the 95% platinum is hallmarked ‘950’.
Platinum is the most expensive metal out of the three.
Platinum is also recognised as the strongest of jewellery metals, and does not require as much care as gold and silver.