Before the use of stainless steel for knife blades (ca. 1920), knives specially made for cutting fruit had blades made of (or plated with) silver, which will not react with the acid in the fruit juice, as a steel blade does, and cause the fruit to discolor.  These knives often have fancy handles made of decorated silver and/or mother of pearl however, those features alone do not a fruit knife make.  True fruit knives have silver or silver-plated blades.  Some (usually American ones) have an additional folding “seed pick” beside the blade. Fruit knives can be entirely made of ivory or bone – even the spring.  (Note: Small (2 1/2″ +/-) metal handled knives, with a bail for attaching them to a watch chain, are not fruit knives.  They are commonly referred to as “gentlemen’s knives.”)  Fruit knives should not be confused with melon sampler knives.