I think any metal that is electro conductive could be plated.I do not think it is wise to keep using the old term of "pot metal" as there are some different alloys that now exist. Interesting thing about the Witness is that I have been able to use G96 Gun Blue cream to blacken the metal. This usually only works on ferrous metals.It also blackens with their anodising solution for aluminium which is quite interesting.
Baz