[noun] [U] - a thin surface layer which develops on something because of use, age or chemical actionHis tomb was covered with a yellow patina of lichen.(figurative formal) Beware their patina of civility, it's only an act.(specialized) Patina (also verdigris) is a blue-green layer that forms on copper or brass.
PATINA
Meaning of PATINA in English
Cambridge English vocab. Кембриджский английский словарь. 2012