We exclusively use 95% platinum ruthenium because it offers the best combination of color, hardness, and workability. It also may be stamped "PLAT" according to FTC guidelines.
One of the great benefits to pure platinum is that it's "hypo allergenic." Well, technically, it's non-reactive, therefore, alloy choice becomes critical in keeping platinum jewelry "non-reactive" or "hypo allergenic." There are several alloys out there that make platinum jewelry reactive - in otherwords, people develop skin irritations. The most notable "reactive" alloy is platinum/cobalt. This alloy was developed with the intent of making platnium easier to cast (but with little concern of the loss of benefit to the end customer). It also adds magnetic properties to platinum...not fun when trying to separate steel from bench-sweeps!
Another reactive alloy would be platinum/copper: the biochemistry of certain people causes them to "leech" copper out of jewelry alloys. Although platinum copper is not as common, it's out there. For more information from the Platinum Guild, click here and here.
2) Polishing compound present on fingers when handling wax: Remember why you send your polishing dust to the refiners? Well, all that gold gets transported into the wax by the oils in the polish! Just like a sponge;especially with injected wax. Therefore, no amount of surface cleaning will help (seriously), and your casting result can expected to be full of surface defects. Would you rather spend a whole day or an hour cleaning your castings?
3) Orange-clean/ orange/citrus smelling solvent. This produces a chemical reaction with the investment and will result in horrible surfaces. Instead, use isopropyl alcohol. Do not clean your waxes in the ultrasonic unless it's dedicated for that purpose (and not jewlery repair).