I want to say the answer is "no," since pure platinum doesn't like to react with pretty much anything other than fluorine or chlorine, but I'm still curious. Stranger things have happened in the world of chemistry.
Can't say I've seen any toning on platinum, either on the 19th century circulating Russian coins or on modern bullion coins.
Here's what I found when I Googled "Platinum common compounds": It is highly resistant to chemical attack. It has stable electrical properties. It does not oxidize in air at any temperature. It will corrode when exposed to cyanides, halogens, sulfur, or caustic alkalis.
I have seen old Pt crucibles which have been used for years to fuse (heat compounds at hundreds of degrees) materials and they appear to tone. I have three old ones I would like to get rid of, where would be the best place?
The folks who sell new platinum crucibles will buy back damaged ones. I don't know whether they pay better than a large bullion dealer or eBay buyers. (Although I've gotten "dead soft" platinum foil, used in dentistry, well below spot price on eBay, so that may not be your best bet if you're selling.)
Maybe. I think by "exposed" they mean "at four-digit temperatures". Platinum crucible manufacturers give a long list of things that you shouldn't melt in a platinum crucible, or place in contact with the crucible when it's very hot. At room temperature, though, the only thing that's going to attack it is aqua regia. No way is a simple salt (a halide or cyanide), alkali or sulfur compound going to attack it at anything less than the temperature of a hot fire.