The most common pigments used are branched carbon, nickel flake, and silver flake. Branched carbon is the form of carbon powder that is the most conductive. It offers the poorest performance among pigments available, but it also offers the lowest price. Carbon paints are better used for grounding rather than as shielding coatings. Nickel is a much better performer than carbon, and it is still reasonably priced.
Nickel is good at standing up to the elements and resisting oxidation as well.
In addition, nickel gives protection against the magnetic portion of EMI, whereas the other common pigments only protect against the electrical portion. Silver conducts approximately five times better than does nickel, gives superior oxidation resistance and, excels at frequencies over 1.8 Gigs, where nickel becomes less effective. Silver, however, costs approximately 25 times as much as nickel, and is therefore usually limited to military applications. Nickel and silver are commonly blended together in shielding compounds to achieve a desired balance in effectiveness and cost. Gold flake is obviously the premium conductive pigment.