Etching is a chemical process in an alcaline solution. This method is used for removing small impurities on the surface, such as for instance oil, dirt, and the ever-present oxide layer. Etching is typically used as a pre-treatment before anodising, but depending on the time the profiles are in the etching bath, different surface finish can be achieved.
Chemical polishing is a process which attacks irregularities in the material giving an even surface. This treatment gives the surface a mirror finish.