NNP

Pickle, Pickling.  Use of a mild acid solution to clean, remove tarnish or corrosion from a metallic surface. Most pickle solutions are made of dilute quantities of sulfuric or nitric acid. If particularly stubborn tarnish exists (as certain oxides) then potassium dichromate is added to the acid solution. A pickle bath (or barrel tumbling, see WHITENING) is often used on blanks to clean them prior to coining or striking. In casting, a pickle bath removes scale as well as other surface impurities.

Some pickling action etches the surface; a process known as descaling. Pickling is widely used in REPOUSSÉ work to remove pitch from the completed work. As with some chemical cleaners, pickling leaves the treated piece with an ACTIVATED SURFACE which will tone or retarnish as it ages unless some further action is done to prevent this.

excerpted with permission from

An Encyclopedia of Coin and Medal Technology

For Artists, Makers, Collectors and Curators

COMPILED AND WRITTEN BY D. WAYNE JOHNSON

Roger W. Burdette, Editor