Pickling apples

On this Wikipedia the language links are at the top of the page across from the article title. Metal surfaces can contain impurities that may affect usage of the product or further pickling apples like plating with metal or painting. Various chemical solutions are usually used to clean these impurities. Many hot working processes and other processes that occur at high temperatures leave a discoloring oxide layer or scale on the surface.

In order to remove the scale the workpiece is dipped into a vat of pickle liquor. Prior to cold rolling operation, hot rolled steel is normally passed through a pickling line so as to eradicate the scale from the surface. The primary acid used in steelmaking is hydrochloric acid, although sulfuric acid was previously more common. Hydrochloric acid is more expensive than sulfuric acid, but it pickles much faster while minimizing base metal loss.

In jewelry making, pickling is used to remove the copper oxide layer that results from heating copper and sterling silver during soldering and annealing. A diluted sulfuric acid pickling bath is traditionally used, but may be replaced with citric acid. For this reason, a thin film of oil or similar waterproof coating is applied to create a barrier to moisture in the air. This oil film must later be removed for many fabrication, plating or painting processes.