What is the number stamping for platinum?
The oldest and most common jewelry alloy for platinum is 90% platinum, 10% iridium. You’ll see various stamps, the most common maybe is 10% Ir Plat or something like that. Occasionally it’s all spelled out, too. A newer alloy is 950 platinum, where the other 50 is usually cobalt. Usually that is stamped 950 Plat. or 950 Platinum. Those are the two most common, anyway.
