The conductivity of the coating will increase as the percentage of pigment is increased. Eventually the increase in conductivity tapers off and it is no longer economical to add more pigment. Pigments in shielding compounds are generally a form of conductive metal flake. The metal chosen will determine how conductive the coating is and how well it will stand up to oxidation and corrosion. Flakes are generally used rather than powders.
Flakes give higher conductivity, because of their great surface area.
Similarly, a big flake will give you better conductivity than a small flake. 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.