Zinc is used to galvanize steel and protect it from rust. Galvanization usually involves coating iron or steel with a layer of zinc, commonly by immersing the object in molten zinc.
The zinc coating provides two forms of protection. It creates a barrier that limits contact between the steel and oxygen or moisture. It also offers sacrificial protection: zinc is more chemically active than iron, so exposed zinc tends to corrode first and can help protect small damaged areas of steel.
Hot-dip galvanizing became an important industrial process during the nineteenth century. Galvanized products include roofing sheets, fencing, guardrails, fasteners, pipes, and structural components. The coating can develop a dull, mottled appearance called a spangle, caused by zinc crystallization as it cools.
Galvanized steel is not rust-proof forever. Severe environments can eventually consume the zinc layer, and cut edges or large damaged areas may require additional protection. Zinc itself forms corrosion products that can slow further attack under many conditions.