Bright Dip. A chemical bath which removes surface impurities on metal and produces a lustrous reflective surface; it is widely used in cleaning metal objects. Bright dip is a process often employed in cleaning blanks for both coins and medals, particularly for proof surface blanks, and also for annealing, electroplating and other finishing operations in the medallic field. Most all bright dip solutions contain nitric acid with one or more other acids: sulfuric, phosphoric, hydrochloric or chromic. Immersion time is from five seconds to five minutes. All bright dip solutions will clean and brighten the metal surface; those solutions that accomplish smoothing as well are called chemical polishing.

Any item which is bright dipped is seldom left in an untreated state (said to have an activated surface), as such the surface is unstable. Bright dipped blanks, for example, should be struck before their surface tones naturally (within, say, three months). An untreated bright-dipped surface will begin to tone or darken after this time by natural means – said to be aged. An aged surface often appears uneven and unattractive. The surface can, at any time, be treated with an artificial toner or any other finishing process.

At the United States Mint in the 19th century a separate room was set aside, called the "whitening room" in which silver blanks were bright dipped. The metal cleaning process continues today, but does not require a special room. See also finish and finishing, reflectiveness.

Reference:

F1 {1962} Graham, pp 183-187.