Etching liquid is a type of ACID used in the process of etching, which is a form of art that involves carving into a surface to create a design. The most common type of etching liquid is ACID, which is typically composed of hydrochloric or sulfuric ACID. It is used to etch metal, glass, and other materials. The ACID eats away at the surface, creating a design or pattern. Etching liquid is also used in the production of printed circuit boards and other electronic components.