Auxiliary Anode

Electroplating involves anodes which comprise the positive pole of the circuit and supply the metal to be deposited.

The plating thickness at any spot on the parts is proportional to the current ("Faraday's Law" ) at that location; but electricity "takes the path of least resistance", so uneven plating thickness is a commonplace, and there may be some areas on the parts which get little or no current (inside diameters, deep recesses), and therefore little or no plating.

Although using them is the exception rather than the rule, auxiliary anodes can address this problem. In concept they are just insoluble wires or rods, connected to the anodic pole of the circuit, and positioned quite close to the parts, in the vicinity of where the plating would otherwise be too thin.