Etching fluids are substances that are used to etch or engrave a surface. They typically contain ACIDS, which are corrosive liquids that can be used to etch metal, glass, and other materials. ACIDS are the most common type of etching fluid, and they are usually composed of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid. These ACIDS react with the material being etched, creating a permanent mark on the surface. Etching fluids are also used in the production of printed circuit boards, as well as for decorative purposes.