Why is the Statue of Liberty that color of green?

PATINA. Why is the Statue of Liberty that color of green? Recently came back from New York. Saw the Statue of Liberty, which brought to mind the topic of corrosion. 

Copper corrodes by reaction with carbon dioxide to form copper (II) carbonate. This distinctive green compound is called patina and prevents the copper underneath from further corrosion. 

A spectacular example of galvanic corrosion occurred in the Statue of Liberty when regular maintenance checks in the 1980s revealed that corrosion had taken place between the outer copper skin and the wrought iron support structure. Although the problem had been anticipated when the structure was built by Gustave Eiffel to Frédéric Bartholdi's design in the 1880s, the insulation layer of shellac between the two metals had failed over time and resulted in rusting of the iron supports. An extensive renovation was carried out requiring complete disassembly of the statue and replacement of the original insulation with PTFE. The structure was far from unsafe owing to the large number of unaffected connections, but it was regarded as a precautionary measure to preserve a national symbol of the United States.

I've learned quite a few new things as an aspiring architectural filmmaker for AL13. This example is one of the most well-known. Why is this relevant to building facades?

When cladding a facade for a building, knowledge of how metal reacts is key. In my time at AL13, we're focused on helping architects create exteriors with a premium look and finish that will last for decades to come.

ACM panels by top manufacturers hold no exception to this fact. Products like the AL13 panel system have coated components to protect against galvanic corrosion.

The one exception is the AL13 I-beam panel stiffener (shipped in mill finish aluminum). This component does not come in contact with anything other than the AL13 (supplied by 3M) two-sided adhesive tape securing it to the backside of the panel. 3M has stated that their adhesive tape is acceptable being used with mill finish aluminum.

Backplates are anodized

Frame components, and Plank profiles are pre-treated, etched and coated

Fasteners are all coated to the highest standards

Not all ACM systems are equal, and not everyone coats their back end components. Research is key.