Some definitive info on platinum, from the Ganoksin Project

[winyan]

Good article from Ganoksin.com: Platinum - Durability vs. Scratching.

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... Pt/Ru has the most tensile strength, whereas Pt/Co has the highest scratch resistance.

There is a major difference between durability and scratch resistance. Platinum is very durable. When scratched, the scratch actually displaces the metal, leaving ridges on the edges of the scratch. This is where durability comes in. Whereas other precious metals, if scratched, lose metal, and thus wear down, Platinum does so at a much slower rate. This is why finishes on other pre­cious jewelry wear off, prongs wear down and the rings actually become thinner and may even wear through with time. Because many gold products, white or other wise, are plated, and plating is creating a hard skin, they seem to have more scratch resistance than Platinum. But soon the plating 'wears off and the material scratches in daily wear.

With Platinum, this is a different story. Many pieces from the turn of the century have engravings that look like new, beads that hold stones appear to be just made and the overall signs of wear seem insig­nificant on Platinum jewelry. A Platinum wedding band will last a life time.

As Platinum scratches, it will develop a patina-like appearance that will last. This is the reason why many designers prefer satin finishes, brushed and sand-blast finishes over the bright polished look.
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win