The so-called "Baths" are the process by which a piece receives the coating of a metal or varnish, this deposition is made delicately so as not to change any texture or detail. Baths can have various utilities, serving to change the color of a piece or avoid the oxidation of it. To happen the bath, the part is placed in a solution that contains the metal to be deposited already dissolved, and with application of electric current the metal is deposited to the surface of the part. There are also pre baths where alkali copper and acid copper baths can be applied before finishing the part. The basic copper bath has high adhesion, serving from substrate to acidic copper. The acid copper bath produces a highly bright layer, is mainly used by its microscopic leveling power and brightness. To receive the bath, all parts that are receiving it need to be with the final polishing, baths cannot remove scratches, or surface textures. Source: bit.ly/2LWi9zw