Traditional nickel plating of shell casings has been used for decades to avoid the green corrosion known as verdigris from occurring when classic revolver calibers were stored in leather utility pouches or ammo loops traditionally used by law enforcement. Nickel plating allowed cartridges to be stored over a much longer period of time without degradation of the brass.
However, traditional single layer systems such as nickel have limitations in their capabilities. Nickel deposits provide corrosion resistance by forming a barrier between the base material and the destructive effects of atmospheric moisture and corrosives such as human sweat. However, nickel must be deposited in a very thin layer to avoid fitment and functionality issues with ammunition components. Thin nickel deposits have intrinsic porosity which allows penetration of corrosives to reach the basis material. Black-TPD® addresses this performance limitation by applying a secondary layer over the nickel which reduces the overall deposit porosity resulting in greatly improved corrosion resistance over a nickel system alone.