The compact metal when exposed to the air tarnishes only very slowly.
The colour is usually pale bronze-yellow, often rather lighter than that of pyrites; on freshly fractured surfaces of pure marcasite the colour is tin-white, but this rapidly tarnishes on exposure to air.
A freshly prepared surface of the metal closely resembles zinc in appearance, but on exposure to the air it rapidly tarnishes, becoming yellowish and ultimately grey or white in colour owing to the formation of a surface layer of calcium hydrate.
This can stop the watch from looking its best as dirt discolors leather and tarnishes metal.
