Rust, Verdigris
For the alchemists, rust and verdigris were the diseases of metals. However, on the other hand, it is especially verdigris that will be transformed into gold, according to the Rosarium philosophorum. "The first philosopher," Thales, said that it is rust that gives the coin its true value, just as the alchemists stated that copper's "greenness" is not a disease, but rather what must be transformed into gold through the work.