BlightRust

Corrosion — the crust of the rust-blight: its pitted lobes and the spines leaning off its edges.

Barely metallic and almost fully rough, so it swallows light where the brass beside it throws it back. That contrast, and the brass slivers left poking out of the crust, are what make a blight read as rust eating the machine rather than as a rock sitting on it.