In the European Union especially, there is a demand for cheaper alternatives to white golds than the palladium whites which are 'nickel-free'. Many new alloys are coming to market, most of which rely on manganese additions as the main whitener. Some are palladium-free and others are low palladium alloys. Chromium and iron are also be used as whiteners. They tend to be hard and more difficult to process. Many of these alloys are not a good white colour, requiring rhodium plating, and many suffer cracking problems and tarnishing.
We recently tried to anneal a batch of white gold from Italy. It was so unmalliable we had to contact the manufacturer, and whilst the solution was simple, a high street working jeweller would find the new metals difficult, if not impossible to process.
Platinum, chromium, cobalt, zinc, tin and silver are all used as whiteners. Silver has excellent working properties but is poor as a whitener. Copper is also added to improve the ductility of most white alloys.
Rhodium Plating
It is important to remember that even the best white gold alloy is actually grey, as is platinum. The white finish you are accustomed to is a rhodium plating, and whatever you are told, white golds are only available in caratages up to 21 carat. It is not possible to have a 22 ct white gold!
Resistance to Tarnish
18 carat and 22 carat gold alloys are almost completely resistant to chemical attack and 9ct alloys are much less resistant. Nine carat alloys can dull or even blacken from exposure to chemicals in the atmosphere, and might discolour in contact with household chemicals. 9ct chain is usually finished with a deeper yellow 18ct or 22ct coating by manufacturers, which is why the bright finish on a new 9ct chain gradually tones down to match other jewellery that you wear on a daily basis.
The original bright finish can usually be restored quite inexpensively by a working jeweller for little cost should your chain become chemically or mechanically damaged over the years.
10:07 AM | 
Posted by
bayan |
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