A study was carried out in a Hull cell in order to optimize the deposition conditions of cobalt ride (black cobalt) in an electrolytic bath, which uses cobalt nitrate for direct obtention of black cobalt. Thermal stability of the material was surveyed on several samples of black cobalt prepared on stainless-steel with a thickness of approximately of 2.5 mu m. It was found that the optical properties change, in respect to the initial values, with time of treatment until an equilibrium is reached. This equilibrium depends on the substrate and the temperature of the treatment used.