Cast iron (grey or ductile) has a unique natural process of corrosion resistance called Patination. Patination is due to the chemical composition of the material and the reaction to atmospheric exposure of the environment. The patina effect is a thin layer of iron oxide (rusty look) is a non-invasive ‘coating’ that prevents deep rusting and slows down further corrosion.
This patina is a typical and predictable trait in cast iron covers and grates which can change depending on the installed location and the amount of traffic the product is exposed to. Many metals have their own version of Patination… bronze and copper can change to shades of green and yellow.
Cast and ductile iron are chosen materials for grates and access covers predominantly due to their corrosion resistance, strength and durability.