Platinum is a chemical element and a noble metal used for watch cases. It resists corrosion, even when hot. Watch brands use it most often as Pt950, an alloy of 95% platinum. Watchmakers choose it for its physical qualities, its resistance to corrosion and the prestige it carries.
What do Pt950 and Pt900 mean?
The number gives the share of platinum in the alloy. Pt950 is 95% platinum and is the standard grade in watchmaking. It is also the platinum alloy that watch brands use most often. Pt900, at about 90% platinum, also turns up. Jewellery is often sold purer still, at a fineness of .999 or .9995. So a platinum watch case and a platinum ring may not contain the same share of the metal.
Why does a platinum watch feel so heavy?
Platinum is very dense. Among metals, only iridium and osmium are denser. A platinum case therefore feels heavier on the wrist than a gold case of the same size. The metal is also hard. The ruthenium-alloyed Pt950 used in watches measures roughly 4.5 on the Mohs scale, so it is harder than 18k gold. Platinum also resists corrosion, even when hot, which is why it is classed as a noble metal.
Why are platinum watches so expensive?
The metal alone does not explain it. By weight, raw platinum costs less than gold, and that stays true after allowing for purity and density. A platinum case holds more metal by weight than a gold case of the same size, because platinum is denser. Even so, the raw material costs less. The metal is only part of the reason for the higher price of platinum watches.
Where it comes from
Platinum is a chemical element. Its name comes from the Spanish platina, a diminutive of plata, the Spanish word for silver. Cartier was among the earliest houses to work the metal into jewellery. In the 1920s the house produced ‘Louis Cartier’ Tank watches with platinum cases. Today, watch brands use it mostly as Pt950.
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