Abstract It is found that in the process of Spark Toughening the conditions of treatment, i.e. the electrical parameters as well as the time of treatment, play a very important role in determining the wear resistance of the treated surface. In general, higher RC circuit capacities than those normally found in commercial machines give improved results. Under conditions of arcing, or with excessive times of sparking, the deposited layer is damaged and in the case of cutting tools the cutting performance deteriorates. Tool life of treated tools depends largely on the hardness and thickness of the strengthened layer, while the hardness itself is closely related to the concentration of hard anode materials in the surface layers.