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Platinum

Platinum is a ductile malleable silvery-white metallic element, very resistant to heat and chemicals. It occurs free and in association with other platinum metals, especially in osmiridium: used in jewellery, laboratory apparatus, electrical contacts, dentistry, electroplating, and as a catalyst.
Symbol: Pt; atomic no.: 78; atomic weight: 195.09; valency: 1-4; relative density: 21.45; melting pt.: 1772°C; boiling pt.: 3827°C (approx.).

Pure platinum works beautifully, it can be readily welded and soldered and takes a lustrous polish, but unless it is finished in a heavily cold worked state, it is too soft for hardwearing jewellery.
Small amounts of certain alloying elements can give platinum the properties that make it ideal for jewellery. Copper, cobalt, gold, iridium, palladium and ruthenium alloy easily with platinum.
In the UK, nearly all Platinum is 950 standard with just 5% alloy.
  Opinions differ on the difficulty of polishing platinum, although once well polished it maintains its finish virtually tarnish free for ever. As with any metal, the polished surface of some platinum alloys may scratch with every-day wear. Johnson Matthey 0.9995 PlatinumMatte finish platinum tends to burnish and highly polished platinum tends to matte a little. With reasonable protection from knocks and abrasion, highly polished platinum can be brilliant and kept that way. A large proportion of platinum-palladium alloy is plated thinly with rhodium, which scarcely alters the colour but does impart some extra wear resistance.

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