NNP

Seawater Surface.  The effect of ocean water on sunken metal over a period of time. Each metal or alloy reacts differently; for example bronze develops a very dark incrustation, silver turns black, gold does not change color but develops a porous surface. As sunken ships are recovered for their treasure these artifacts are almost always treated to enhance their appearance. It is in this state they are frequently sold to collectors, but the surface bears evidence of their long buried existence.  Compare fountain coin.

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