From a practical perspective, platinum is much softer than white
gold, so trade one problem for another, rhodium wears off, platinum
can look scratched up and dull fairly quickly,
Which alloys? treated in what fashion? I work with one platinum
alloy that is well over 300 HV when heat treated that is getting into
the hardness range of tool steel (and quite a bit harder than any of
the "white" golds). Some of the 950 Palladium alloys are in the same
hardness ballpark as the "white" golds and are truly white. There are
some "white" golds that are softer than 18 k yellow. It is not just
the metal it is how it is treated both before you get it and what you
do to it that will affect how hard or soft it is. More workable
"white" gold alloys often are quite yellow, there is almost always a
trade off between physical and mechanical properties when talking
about "white" golds performance.
I have had some customers show me their engagement ring (bought
somewhere else) and ask why it is discolored and then react very
negatively when told it is a plating process that made that
yellowish metal look white and some don't seem to care.
There are many factors to this question about to plate or not to
plate and what alloys to use for what work, but the bottom line is
no matter how you do it plating wears off. So if you plate you need
to disclose that fact to the customer or deal with the surprise and
possibly bad feelings when they realize their ring is not white.
James Binnion Metal Arts