Platinum is a naturally occurring white metal. White gold is created as an alloy of the naturally occurring gold with white metals like silver and palladium to get a white hue. In addition, white gold pieces are often covered with a thin plating of rhodium, a platinum group metal, for strengthening and a whiter appearance. Platinum and white gold resemble each other aesthetically, but differ in composition, density, hardness and other properties.
edit In Chemistry
Platinum is a chemical element with the atomic symbol Pt and an atomic number of 78. White gold is an alloy of gold and has the same symbol as gold Au.
Platinum is a natural white metal, while white gold is given its color artificially by alloying gold with silver or palladium and by adding rhodium plating to it. Nickel used to be a very popular metal used to create white gold, but is no longer used as much since there were studies  showing its adverse effects.
Platinum has the most luminescent white hue of all metals used for jewelry.
White gold has the same properties as yellow gold. So if 18-karat yellow gold is made with 75% gold and 25% other metals like cooper and zinc, 18- white gold is made of 75% gold mixed with 25% of whiter metals, like silver and palladium. It is highly reflective and is not subject to tarnish.
Platinum is also highly reflective and is 60% denser than gold. Platinum is purer than white gold. Measured in parts per thousand, platinum jewelry is typically 850-999 parts pure platinum (85%-99.9%), with the remainder made up of other metals. White gold isn't as pure or durable. Platinum is denser, heavier and stronger than white gold. Platinum is heavier (specific gravity: 21.4) than gold (specific gravity: 19.3). Platinum is 60% more dense than Gold.
White gold is has very high reflectivity and therefore shines much brighter and whiter when new. Platinum also has a shine, but it does not last very long. The rhodium in both white gold and platinum eventually wears off giving a dull grey look, but the shine can be replaced by re-plating the rhodium.
While both metals are extremely durable and can last for years, platinum is heavier and slightly more durable than white gold, and loses very little weight in daily wear or polishing. Both platinum and white gold have to be periodically re-plated to maintain the shine, although platinum can go longer without being replaced or re-plated.
Platinum is rare. Ten tons of platinum ore is required to process a single ounce of pure platinum. White gold isn't rare since its base (yellow gold) isn't very rare. Platinum is said to be 35 times rarer than gold. This is also one reason which makes white gold cheaper than platinum. Platinum is almost 3 times the rate of white gold.
All precious metals can scratch, and platinum is no exception. However, the scratch on platinum is merely a displacement of the metal and none of its volume is lost. Over time platinum develops a natural patina, which many people find just as attractive as a polished finish. Platinum does not micro-scratch the same as Gold, but actually “furrows” instead. On the other hand, when Gold is micro-scratched, the Gold metal is actually removed. Sometimes these micro scratches can leave white gold looking a bit yellowish
edit Allergic reactions
In order to obtain pure platinum, the ore is crushed, made into a slurry, and then mixed with a detergent containing 'collector' molecules. Air is then blown through the mixture, enabling the grains of metal minerals to be separated from the rest of the mixture. This process is called "flotation" or "mineral beneficialness". The next step is smelting. White gold is made by alloying yellow gold with metals like nickel, palladium etc in different proportions.
Platinum is used in jewellery, laboratory equipment, electrical contacts, dentistry, and automobile emissions control devices. White gold alloys can be used for different purposes; while a gold-nickel alloy is hard, strong and therefore good for rings and pins, white gold-palladium alloys are soft, pliable and good for white gold gemstone settings.
Platinum is a better quality metal than gold. White gold, since made from gold, has a chance of wearing off it's white hue and hence isn't of the best quality in this context. The highest quality white gold is usually at least 17 karat, and made up of gold and palladium, sometimes with trace levels of platinum for weight and durability.
Prices for white gold and platinum are constantly changing. While prices for both metals have come to be fairly comparable, platinum is still more expensive than white gold on account of the following:
- Platinum alloys are usually purer than white gold
- Platinum is denser, so more metal is needed to make a ring the same size as white gold
- Platinum is more difficult to work with and most often requires really fine craftsmen, increasing the labor costs