or muriatic acid. Name used for hydrogen chloride, placed on the market as an acid or muriatic acid. In pictorial treatments, it is most noted in the preparation techniques for mural supports, where it is used to 'burn' eventual traces of saltpetre and mold on the first layer of the intonaco before the application of the arriciato (with the prudence to successively neutralize its action with several washes). It is also used in the fabrication of many colours.