Because zinc is a metal, it is non-porous and will not stain in the traditional sense of the word. Zinc will oxidize and patina which is a chemical change that produces a different color in the metal. It oxidizes rapidly and will move toward a blue gray color. Almost anything that comes in contact with it will oxidize it to some degree. It can be maintained with or without a patina. A full patina does take some time to develop ( typically, a year or more).