I was surprised exactly how patination is both art and chemistry; controlled oxidation, acids

https://damienmnbq110.cavandoragh.org/salvo-metal-works-and-the-truth-of-copper-customized-smokeshaft-shrouds-that-endure

I marvelled how patination is both art and chemistry; managed oxidation, acids, and waxes produce living surfaces that develop with climate yet stay protectively sealed.