True. Atomic weights. But Pt is somewhat close to silver, Ag. Here are some common metal atomic weights.
Fe 55.845
Cu: 63.546
Ag: 107.87
Pt: 195.08
Au: 196.97
Pb: 207.2.
A quick way to test a metal is to weight it and then put it in water container to see how much displacement you get (volume). This will work for relatively large differences in density. Now, if you went through customs with a unpretentious Pt bracelet, I doubt anyone is going to notice. Likewise, if you make car parts like a steering wheel or part of a frame out of Pt, not many will think of this unless someone has tipped off the agent.
The other thing you can do is gold alloys with copper. Most gold coins are mixed with a little copper to make it stronger and stiffer. You can increase the copper content and the gold will take on a browner hue and look more like copper or brass. I have some “Swiss Miss” coins and if you put them in with pennies, you really can’t see much of a difference based on color.
Very interesting, especially about the Swiss coins.