Acid dips can be used to clean different types of metal. Different acids work better with different metal compounds. Some of these acids stop oxidation and clean away rust. Other acids are better suited for removing metal discolouring such as tarnish on silver. You need to research the types of acids best for the metal you are working with, as certain acids will destroy certain metals. You want to be sure to pick the right acid for your project.
Chemical or acid submersion seems simple when you talk about dipping a silver charm. But cars that have been entirely coated with rust can be dipped in hydrochloric acid to remove all of the rust. This type of acid dip requires a very large vat, a lifting device and a steel chain and holder that can also handle the acid. Phosphoric acid can also be used as well. Both acids are warmed for the dipping process and the metal must only stay submerged for a short time as otherwise it can become brittle if exposed to the hydrogen in the acid for too long. Steel is the best type of metal for this particular acid dip.
Auto bodies can also be dipped in order to remove all paint. A benefit of doing this as opposed to sand blasting is that every single area of the body gets treated. When sandblasting, the gun can miss some areas, especially those that are not readily visible. Usually you will do a quick sand blast prior to dipping to weaken the paint. After the body finishes in the acid dip, a protective coating can be put on the metal so you do not have to repaint it immediately. This coating prevents any flash rusting and gives you additional time; this can be useful if you are restoring a car and need time to get parts.
Acid dip for copper cleaning consists mostly of salt and vinegar. The acid in the vinegar eats through the cupric oxide, copper sulphate, and copper chloride that tarnish copper. Caustic soda is another acid base that can be used. You can dip the copper in a small vat with a wire grate to lower the copper into the substance. Make sure to work with any of these substances in well-ventilated areas.
Dips are most often used with silver that has developed a thick, black tarnish. Dipping the silver should be a quick process because the metal can become damaged if you leave it in the acid for a long period of time. Jewellery stores sell a less caustic version of the silver dip, making it harder to ruin your pieces. You should not use dips on any silver used for eating that contains a hollow area. It is easy for the acid to get trapped in the hollow portion and it can poison food. In non-food bearing silver, you should still be wary of hollow areas as the acid will slowly weaken any coating and cause the silver to become porous and weak.