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Mechanical Properties of Platinum Jewellery Casting Alloys

There is scant data available in the literature evaluating fitness for purpose of platinum alloys used in the creation of jewellery designs (1–8). Only recently has literature on basic properties of platinum jewellery alloys been published (9, 10). In an industry steeped in tradition and ruled by millennia of hands-on experience, this fact is not surprising. Rather, a substantial body of tribal knowledge exists concerning what does and does not work and for many years this was largely sufficient. Enter the digital revolution where cast versus hand-fabricated products now dominate and tribal knowledge alone is no longer enough. This is true because the two methods of production result in very different material properties and this difference can affect the end consumer’s experience when it comes to wear resistance. Take, for example, the common platinum-iridium alloy Pt90-Ir10. This alloy was used to create much early 20th century platinum jewellery and a good amount of this jewellery is still in circulation today. And though purely anecdotal, there is substantial evidence that such platinum estate jewellery has stood up quite well to the test of time, remaining strong and resilient despite decades of daily wear. But is this still the case when legacy alloys used in hand fabrication are used to make jewellery in a purely cast form? In past eras when the vast majority of platinum jewellery was hand fabricated, the metal was bent, formed, twisted, compacted and hammered into the desired shape. All of these hand-working methods introduce work hardening, a mechanism by which the hardness and strength of the metal is increased through deformation of the crystal lattice. Consequently, most hand-fabricated platinum jewellery tends to be inherently strong. Contemporary jewellery designs, on the other hand, are almost entirely produced through casting and not likely to experience the benefits of work hardening. Therefore, platinum alloys that were once viewed as robust are now found to be lacking in their cast forms. Given that today the labour savings achieved through casting near net-shape jewellery is nothing less than an economic imperative, it is necessary to take a closer look at platinum alloy choices to determine suitable strength levels for cast product. Mechanical Properties of Platinum Jewellery Casting Alloys