Many original ships used copper nautical lights due to their resistance to corrosion and longevity. Many vintage lights as well as some of our reproduction lights use a high quality copper metal in their construction. Copper will withstand the harsh salt water environment and will eventually turn a nice shade of patina green when left unpolished.
It has been said "copper alloys are metal alloys that have copper as their principal component. They have high resistance against corrosion. The best known traditional types are bronze, where tin is a significant addition, and brass, using zinc instead".