Abstract: Metal surfaces are refined, by the process of the invention, to high levels of smoothness in relatively short periods of time. A liquid substance is utilized to produce a conversion coating on the surface of the parts being treated, which are agitated, while being continuously wetted by the substance, in a mass finishing unit. Abrasive action causes the relatively soft coating to be removed from the high points of the surface, while leaving substantially intact the coating on the lower surface areas, with the coating being continuously repaired over metal exposed during operation. Fillage of the finishing unit container ensures efficient agitation and continuous oxygenation of the liquid substance, thereby maintaining a desirable rate of reaction and a high rate of surface leveling.