The etchant for martensitic chromium steels is mainly used in metallography. Its formulation includes aqua bidest, fuming hydrochloric acid, copper dichloride dihydrate, ammonium heptamolybdate tetrahydrate and ammonium monovanadate. It acts on the surface of martensitic chromium steels, a subgroup of stainless steels, exposing their microstructural features. Fuming hydrochloric acid (HCl) serves as the etchant, while copper dichloride dihydrate (CuCl2.2H2O), ammonium heptamolybdate tetrahydrate ((NH4)6Mo7O24.4H2O) and ammonium monovanadate (NH4VO3) act as active components that modify and make specific the etching processes. These chemical reactions produce visualization of microstructures and phases in the treated steels. These allow detailed analysis of material properties and performance, as well as defects or changes in the material. The effect of this solution is specialized in revealing structures within martensitic chromium steels.