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.
Gold flake is readily available, but its high price limits its use. Aluminum and copper are generally not used as conductive pigments. Both of these metals are highly reactive and their flakes are generally completely covered with oxidation and therefore not electrically conductive. A new generation of coated metal flakes is now becoming the pigments of choice in many applications. The aim of these coated flakes is again to achieve a desired balance between cost effectiveness and performance.