I was surprised just how patination is both art and chemistry; regulated oxidation, acids

https://tysonzymk871.yousher.com/hand-fabricated-copper-cupolas-what-architects-know-and-time-verifies

I marvelled exactly how patination is both art and chemistry; controlled oxidation, acids, and waxes produce living coatings that evolve with climate yet continue to be protectively secured.