What is a coin with Shipwreck Effect?
Generally, this impairment consists of microscopic coralline structures embedded in their surfaces or etching of the surfaces due to being immersed in saltwater. This latter is often referred to as saltwater etching.
The term shipwreck effect was originally coined by numismatist John Albanese to describe many of the silver Seated Liberty half dollars recovered from the S.S. Republic shipwreck. It was included on coins encapsulated by Numismatic Guaranty Corporation (NGC).
More recently, shipwreck effect has been used to describe coins recovered from the S.S. New York shipwreck.
NGC has since divided their shipwreck effect designation into subdivisions, in essence, giving the coins a grade.