the hardness of a metal by pushing a pyramidal diamond into the surface of the metal with a predetermined load and then measuring the penetration. The deeper the impression, the softer the metal. This parameter does not measure strength, which is measured in pounds per square inch (psi), or in the metric equivalent. (Newtons per square meter). Durability is determined primarily by strength, and scratch resistance is determined by hardness.

Here is a comparison of these properties for platinum alloys:

As you can see, the Pt/Ru alloy has the highest tensile strength, whereas the Pt/Co alloy has the highest hardness and,hence, 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. Many white gold products are rhodium-plated, which creates a hard skin, they seem to have more scratch resistance than platinum, but the plating wears off and the material scratches in daily wear.

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