Despite its popularity on the jewellery market for many years, the nature of white gold remains secret for many people, some of them wearing it every day. Some people think white gold is an alternative metal from the same family while other are under the impression that it is just another name for platinum. And them to make the things worst comes the rhodium plating.
In order to achieve certain properties of the precious metals necessary for jewellery making, jewellers are not using them in their pure form, but mixing them with other metals. This process is called alloying and the resulting mixture is called alloy. One of the properties which changes when alloying gold is its colour. In pure form gold is always yellow. In fact gold and copper are the only metals in nature which have colour in their pure form. Depending on the amount and type of other metal added to the alloy we have different colour and different purity. The purity standard for gold alloys in South Africa is 9 karat with 37.5% of fine gold in the alloy and 18 karat which has 75%. This is the reason why 18k gold is almost twice the price of the 9k one. It has twice the amount of pure gold in the mixture.
The alloying metals, which are the metals added to the pure gold in certain gold alloy, are responsible for its final colour and mechanical properties. In order to get a gold alloy of white colour is necessary to use whitening metals in order to overcome the natural yellowness of the gold. It is usually a combination of few white metals, each of which brings partly its qualities to the resulting alloy. The most common metals used for alloying white gold are silver and palladium.
While the aim is to achieve the whitest possible colour, some of the yellowness of the pure gold in the mixture always bleeds through. This brings about the necessity of rhodium plating. Some people like the natural colour of the white gold, however most of them prefer it brilliantly white, especially when it comes to diamond jewellery. All white gold alloys used for engagement rings in South Africa are rhodium plated by default.