What are the different screw coatings?

Some screws, usually those designed for outdoor use, have special coatings which can help protect against rust or corrosion.

Zinc yellow passivated screws

These types of screws have been subjected to an electroplating treatment and coated with a yellow dye.

Manufacturers claim that this process gives the screw a more aesthetically-pleasing appearance, as well as offering extra protection against corrosion.

Black japanned screws 

Screws with a black japanned finish have been coated with a thick black lacquer like an enamel paint.

Manufacturers of these screws claim that the coating gives a decorate finish and helps to prevent rusting.