Rhodium is shiny and very colorless. Like Chrome plating. Platinum is somewhat difficult to bring to an equally high polish, but it certainly can be done. The nature of platinum is a more silvery gray-colorlessness. Most platinum does not really need to be rhodium plated, but rhodium does cover over some gold solder and assembly issues. Its a rather cosmetic treatment, not any sort of permanent mask. It does make a piece look very fresh in the showcase.
You know Dave and Steve, I read a posting in another forum where all the bench workers were in agreeance that you MUST NOT rhodium plat platinum, one said you should leave the job (but not that nicely), if you do! Absolute bollocks! Glad the people here have good sense.
To me - Platinum is where rhodium is good.
It is in the same metal group, which is important, but more then that, it adds a quality:
Under the diamonds, the plating won''t come off and the extra whiteness and luster enhances the diamonds and invariably improves the brillianmce of the settings. It wont cover scratches - it accentuates them. Pok marks will not even take the plating so they become painfully obvious after plating, so you can''t allow any polishing defects. In that way, it forces the manufacturer to use tougher quality controls.
As far as covering gold solder, well I personally never use gold solder. I have an oxy-propane tourch set-up, hot enough to deal with platinum solder, or I can fuse, others laser weld. It is a very bad practice.
It does come off (not as fast when done right as Steve said) but on platinum it isn''t very noticeable, especially on ruthenium alloys. It isn''t all that important to re-plate, where it is hard to spot. The lasting benefits are allready there under the diamond.
Rhodium plating w''g alloys you to alter and hide their colour on a non-permanent basis. Nothing about this makes me feel good, though I don''t mind using it to enhance a diamond and in good coloured white gold like palladium+ alloys.