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Gold jewellery is made of several different alloys as pure gold is too soft. The amount of gold is measured in karat, from 9 karat up to 22 karat. By varying the alloys different colored versions can be made, from the common rose gold to the green tinted green gold. Even white gold can be made by alloying with nickel and palladium. Alloying with copper gives red tones while silver moves it towards green.
Silver jewellery is often made from sterling silver which is 92.5% silver and 7.5% copper.
Platinum jewellery is made of several different alloys but all are high in platinum content. Some common alloys are :
- PT900/100Ir with 10 % iridium
- Pt950/50Ir with 5% iridium
- Pt950/50Co with 5% cobalt
- Pt950/50Ru with 5% ruthenium
- Pt950/50Ir with 5% palladium
(Main article : Stone removal)
A lot of jewellery contains precious stones and can be a good source of revenue if the stones could be removed without damage. A problem with stones set in karat gold is that the alloy is often based on silver and gold in amounts to make it resistant to aqua regia when the surface is covered up by silver chloride.
This can be overcome by several methods but most of them are labor intensive, like repeatedly switching between dissolving gold and dissolving silver chloride.
Some jewels can also be highly sensitive to the acids used in refining and would be damaged by the temperatures used in melting the metals. Then the only alternative left is to remove stones one by one with mechanical means, grinding and filing off the mounting points.
- GRF : How to estimate the amount of gold in electronics and jewelry
- Wikipedia : Jewellery
- Wikipedia : Colored gold
- Wikipedia : Sterling silver