Platinum is an element on the periodic table, a metal in its own right, while white gold is an alloy of pure yellow gold and other metals. Here is a bit of history:
In the late 19th century bench jewellery was revolutionised by the invention of the
pressurised oxygen tank, or liquid oxygen, which for the first time became
commercially available at affordable prices. This led to the development of the
oxyacetylene mixing torch, invented in France by Edmond Fouché and Charles
Picard, and for the first time made possible a flame that could reach the
temperatures required for solid platinum (Pt) jewellery manufacturing.
Platinum quickly emerged as the new darling in the world of fine jewellery, with its
brilliant white colour it complimented white diamonds, which thanks to De Beers
were having a moment at the same time too, and its fantastic tensile strength
made extremely delicate designs possible for the first time in history.
With the end of the Edwardian era and the start of WWI, platinum all but disappeared in
jewellery, due to its usefulness as a catalyst in explosive devices but
experienced a brief period of resurging glory (the Art Deco period) between the
great wars, mostly thanks to the discovery of the Merensky Reef, a platinum
deposit which stretches from northern Gauteng into Mpumalanga and Limpopo.
During WWII the US government declared platinum a metal of strategic importance, and almost
completely banned its use in anything outside of military applications. This
led to the development of a new gold alloy we know today as white gold.
White gold is a mixture of pure yellow gold and other metals such as silver, copper and
zinc, which are common in other gold alloys, but with the addition of palladium
or nickel to bleach out the yellow colour. Because its base is still yellow
metal, it isn’t quite white and is usually plated with another, whiter metal to
create the crisp white finish consumers expect. This used to be done with
rhodium (Rh), but after that metal’s price skyrocketed in recent years, it has
been replaced by other metals.
Nickel alloys have almost completely fallen out of use because most people are
allergic to them. It perseveres in mass production white gold jewellery though,
so be sure to ask before you make a purchase. My preferred alloy contains 10%
palladium. Although the palladium content makes it quite a bit more expensive
than the nickel alloys, it has good tensile strength, is unlikely to cause
allergic reactions, and has a white enough finish for it to still appear white
even without the plating.
Because it contains gold (Au), white gold alloy fineness (purity) is expressed the same
way as yellow gold, in karatage (9K, 14K, 18K) or parts in 1000 (375, 585, 750). In South Africa platinum jewellery is usually 95% pure Pt, with a 5%
copper or ruthenium alloy.
You can read more about the composition of white gold here.
