Like most metals, cast iron undergoes a natural oxidation process, resulting in an outer protective coating known as rust. This process is called ‘patina’.

Patina is a naturally occurring process and should not be confused with corrosive rust. Patina is good for iron as it provides a protective layer, as it is a thin layer of oxides on the surface that acts to slow down further corrosion. Therefore patina on cast iron grates does not harm the structural integrity. This ‘rust’ layer shields the cast iron from further oxidation. Think of rust as a corroded armour that protects against additional corrosion. This property allows iron to remain strong & intact for several decades. Unlike steel, cast iron is durable and will not flake. The patination of cast iron grates is predictable & the duration of each stage depends on local moisture conditions, foot traffic, foreign substances etc.

Once the oxidation process begins, cast iron will turn a bright orange then fade to a chocolate brown, similar to the colour of manhole covers.

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