Method of producing magnetic films

A method of electroplating as cathode an elongated substrate 12 such as a plastic dielectric web 14 having a thin conductive film coating 13 which may be formed by chemical plating comprises passing the substrate through the bath and applying a plating current between it and an anode at a point such that due to the resistivity of the substrate the current density at the surface of the substrate decrease from a value exceeding the limiting current density for the material (IL) being deposited, i.e. the current density at which all the plating ions brought to the cathode are discharged or reduced to a lower valence state, to a value less than this as the substrate passes through the bath, the curve 20 representing the plating current. As described, the method is applied to depositing magnetic Ni-Co alloy or Co films from acid baths containing sodium hypophosphite and ammonium chloride on to a dielectric resin web coated with an electroless Ni film containing 2-12% phosphorus.