NNP

Residual Toning.  A toning occurring after a lapse of several years. Most oxidized and relieved bronze and silver medals – even though they are lacquered – may tone or slightly darken under the lacquer years after their manufacture. This is a result of the oxidizing or darkening chemical in the finishing process (as ammonium sulphide) slowly reacting in time. Relieving removes most of the darkening chemical from the object's surface, particularly the high spots and the fields, but traces of the chemical even remains on these areas, and some remains in the crevices.

Gradually and slowly over time this darkening chemical will still continue its work. Most residual toning, however, is uniform and not unattractive. Should the relieving not have been performed properly the residual toning may emphasize this. wipe marks are a form of residual toning (since they only appear after a lapse of time), they are irregular shades and are considered unsightly. Of course, they can, as with any unsightly finish, be easily removed by refinishing.

excerpted with permission from

An Encyclopedia of Coin and Medal Technology

For Artists, Makers, Collectors and Curators

COMPILED AND WRITTEN BY D. WAYNE JOHNSON