patina
noun uk/ˈpæt.ɪ.nə/ /pəˈti.nə/ /ˈpæt.ɪ.nə/
[ S ]（物体表面的）薄层
a thin surface layer that develops on something because of use, age, or chemical action
His tomb was covered with a yellow patina of lichen. 他的墓地上长了一层薄薄的黄色地衣。
[ S ] formal假象
something that makes someone or something seem to be something that they are not
Beware their patina of civility, it's only an act. 当心他们礼貌、客气的假象，那只不过是在装样子。
[ U ] chemistry specialized（铜器表面的）铜绿，铜锈
a blue-green layer that forms on copper, brass or bronze