Why is platinum often alloyed with iridium?

Platinum is often alloyed with iridium because pure platinum is relatively soft, making it susceptible to scratching and marring. Adding iridium—typically in concentrations ranging from 1 to 30 percent—creates an alloy that is significantly harder, stiffer, and more resistant to chemical attack than pure platinum, while still remaining readily workable.1234

These enhanced physical and chemical properties make platinum-iridium alloys ideal for a variety of specialized applications, including:

• Jewelry: Providing durability for intricate designs.34
• Medical and Scientific Tools: Used for surgical pins, pivots, and laboratory equipment.341
• Electrical Components: Highly resistant to high-temperature electric sparks, making the alloy suitable for electrical contacts and sparking points.341
• Standards of Measurement: Due to its stability and resistance, a 90 percent platinum and 10 percent iridium alloy was historically used to construct international standards for the metre and the kilogram.341