The coatings do not affect the magnetic strength or performance of the magnet. The preferred coating is dictated by preference or by the magnets intended application. Nickel is the most common choice for plating neodymium magnets, and is actually a triple plating of nickel-copper-nickel. It has a shiny silver finish and has good resistance to corrosion. Black nickel has a shiny, black/charcoal appearance and is slightly more corrosion resistant than regular nickel. It is also a triple plating of nickel-copper-black nickel. Zinc has a dull gray/bluish finish, that is more susceptible to corrosion than nickel. Zinc can leave a black residue on hands and other items. Epoxy is basically a plastic coating that is virtually 100% corrosion resistant as long as the coating is intact. From our experience, it is the least durable of the common coatings. Gold plating is applied over the top of nickel plating, so gold plated magnets have the same characteristics as nickel plated ones, but with a gold finish.