Neodymium belongs to the rare earth metals and is a special material: in combination with iron and boron (Nd2Fe14B), it can be used to produce the strongest permanent magnets currently available in the world.
Most NdFeB magnets are nowadays produced in China. The reason for this is that 97% of one of the starting materials, neodymium, is mined and extracted in China.
The mangle has a nickel-copper-nickel coating. This gives them an attractive silver surface.
Available here as pack of 8 with many different depths.