I marvelled just how patination is both art and chemistry; controlled oxidation, acids

https://www.scribd.com/document/1039773992/Finials-That-End-Up-Well-100-Years-of-Copper-Integrity-146161

I was surprised exactly how patination is both art and chemistry; regulated oxidation, acids, and waxes produce living coatings that develop with weather condition yet stay protectively secured.