or Caustic Soda. Chemical compound obtained through the electrolysis of a water solution of sodium chloride in special cells. It is utilized, among other things, for the fabrication of soaps, lye and paper. Thanks to rapid cleaning results, it was amply used between the 18th and 19th Centuries on paintings, with devastating results due to both strongly aggressive behavior and to its capacity to continue a solvent action, especially in the presence of humidity.