Alloy Comparison
In its pure form, platinum has a hardness of 40 HV. This is very soft and makes pure platinum unsuitable for jewelry. (An exception is some specialty micro-alloyed high-purity platinum used mostly in Japan and Europe, which has a hardness of about 160 HV.)

As a result, platinum is typically alloyed with one or more other metals to make it harder, and thus useful for jewelry. There are many metals that can be used for this purpose, including copper, tungsten, gallium, indium, or one or more platinum group metals (PGMs), such asrhodium, ruthenium, osmium, iridium, and palladium.

Each alloying metal imparts different properties to the platinum alloy, and which is selected depends on the

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desired result. There are alloys designed for casting, fabrication, machining, and heat treatment (which increases the alloy's hardness).

In this article, we will focus on the alloys most commonly used for jewelry production in the United States: platinum 950/cobalt 50, platinum 950/ruthenium 50, platinum 900/iridium 100, and platinum 950/iridium 50. There is also heat-treat-able platinum, which is 95 percent platinum, with the remainder being mostly proprietary or patented.

As indicated in the following chart, platinum/cobalt, platinum/ruthenium, and the heat-treatable alloys are hardest, and therefore offer the highest scratch resistance.

It is also clear that 95/5 platinum/iridium is softer and not as strong