Different Coatings
Neodymium magnets are usually coated to protect them from rusting. This is because they are made from a sintered powder containing Neodymium, Iron, Boron and small quantities of other rare earth elements. The coatings can change the appearance of the magnet drastically, but it doesn’t change the magnets properties in any other way.
This photo shows a Nickel-Copper-Nickel plated 29mm x 10mm magnet in the top right corner. This is the most common coating and it gives a bright, shiny ‘silver’ appearance. However, it is not suitable for damp conditions because the nickel is porous and it only takes a tiny scratch to breach the Copper layer which then leads to the potential for the iron in the magnets to start rusting.
The Zinc plating is a very hard wearing finish. It’s not porous so it can be used in damp conditions, but we would still recommend coating magnets with a metal paint (such as Hammerite) or an enamel paint or a lacquer, just for peace of mind.
The bottom magnet has a passivated coating, in this instance, Phosphate. This is simply to prevent the magnet rusting. It often looks quite dirty, but this is entirely normal and it does not affect the magnet in any way.