Information on White Metals used in Jewellery.

Palladium is a rare and lustrous silvery-white metal that was discovered in 1803 by William Hyde Wollaston, who named it palladium after the asteroid Pallas. Palladium and Platinum are part of a group of elements referred to as the platinum group metals (PGMs). Platinum group metals share similar chemical properties, but palladium has the lowest melting point and is the least dense of these precious metals. Palladium itself has been used as a precious metal in jewellery since 1939, as an alternative to platinum or white gold. This is due to its naturally white properties, giving it no need for rhodium plating. It is slightly whiter, much lighter and about 12% harder than platinum.
Palladium is one of the three most popular metals used to alloy with gold, making white gold (silver can also be used.) Palladium-gold is a more expensive alloy than nickel-gold, but it's naturally hypoallergenic and holds its white colour better.
When platinum was declared a strategic government resource during World War II, many jewellery bands were made out of palladium. As recently as September 2001, palladium was more expensive than platinum and rarely used in jewellery also due to the technical obstacle of casting. However the casting problem has been resolved and its use in jewellery has increased because of a large spike in the price of platinum and a drop in the price of palladium.
The popularity of Palladium jewellery is expected to grow in 2010 as the world's biggest producers embark on a joint marketing effort to promote Palladium jewellery worldwide.

Platinum is more durable than other metals, and is heat and acid resistant. Platinum does not wear away and holds precious stones securely. Platinum's wear- and tarnish-resistance characteristics are well suited for making fine jewellery.
Platinum is more precious than gold. The price of platinum changes along with its availability, but its price is normally more than twice the price of gold. It has a naturally white lustre that helps to reflect the true brilliance of diamonds. It keeps its pure white colour for a lifetime and is hypoallergenic. If all the platinum ever mined was poured into an Olympic swimming pool, it would be scarcely enough to cover your ankles.

White gold is an alloy of gold and at least one white metal, usually nickel or palladium. Like yellow gold, the purity of white gold is given in carats (karats).

White gold's properties vary depending on the metals and proportions used. As a result, white gold alloys can be used for different purposes; while a nickel alloy is hard and strong, and therefore good for rings and pins. Gold-palladium alloys are soft, pliable and good for white gold gemstone settings.
The highest quality white gold is usually at least 18 carat, and made up of gold and palladium, sometimes with other metals like copper, silver and platinum for weight and durability, although this often requires specialized goldsmiths.
While some higher-quality white gold alloys retain their shine and lustre, most will be coated with a very thin layer of rhodium. This gives the naturally more-dull white gold a shine comparable to platinum or silver; however the rhodium may wear off over time.