Verdigris (pronounced verdegree) is best known as the effect on metals such as brass and copper when they're exposed to weather or seawater. In a short space of time they go from bright and shiny to a dull blueish-green. It's commonly scene on roofs, pipework and weather vanes.
The verdigris can be polished off, but will soon form again.
Historically verdigris was used as a pigment for artists, producing the most vibrant shade of green available in the middle ages.
Did you know that verdigris can also be used to describe sailors? I guess it could be quite apt if they're under the weather.
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