A method and apparatus for graining a surface having a substantial area traveling at a substantial rate of speed. The method includes directing the surface past an array of electrical arcs traveling about a plurality of loop electrodes arranged to provide overlapping arc loop paths as the surface travels past the array of arc loops. The arc loops are established between the loop electrodes and the traveling surface, and thus contact the surface to grain the same. When each arc is struck between its loop electrodes and traveling surface, it is magnetically impelled about the loop of its electrode by a magnetic field established perpendicular of the direction of arc current flow. An annular sheath of gas is provided on each side of the electrode loop and the arc struck between the electrode loop and the traveling surface.