801 Grand - The roof is made out of copper sheeting that was designed to form a green coating of verdigris over time, much like the Statue of Liberty. However, unlike New York City, the air salt content in Des Moines was so low that the desired oxidation process failed. The result was the copper turned a dark brown. Discussions on possible removal of the top layer of copper that would allow crews to purposely cause the oxidation process to create verdigris resulted in the decision to leave the roof as is in its current state. - wikipedia