The inorganic soils, which include rust and tarnish, solid particle dirt, scale, smut, and cleaning residues, are usually removed by alkaline degreasing or an acid pickle. Rust and tarnish, being insoluble be alkaline degreasing or an acidic or alkaline chelating solutions, with or without electric current. Water insoluble solid particle often adhere to oil present on the surface and are therefore removed simultaneously with the oil. Smuts which result from pickling are very troublesome and should be avoided. Inorganic cleaning residues may be films of oxides, phosphates, silicates, and the like remaining on the metal surface after alkaline cleaning and not removed by the rinse and mild acid dips that follows. Care in rinsing is the best way to eliminate trouble from this source.
Not all plating operations require the same degree of cleanliness of the basis metal. It is possible to plate from an alkaline cyanide plating solution articles that are dirty compared to those that may be processed in acid plating baths such as nickel. Therefore, a much shorter cleaning cycle may be employed for alkaline cyanide plating. It is poor practice, however, to contaminate a plating solution by using it as a combination cleaning and plating bath.