Platinum is typically mixed with another alloy. So there's platinum-iridium, which tends to be easier to cast and work with. Platinum-iridium is a whiter metal, but it's also softer so it doesn't tend to be as durable. The other popular form of platinum is platinum-ruthenium, or platinum Ru. Platinum Ru is a much harder material, but it's a little harder to polish and finish. It also has a bit of a gray tint to it. This is why you see a little bit of variation between different types of platinum.