“a surface appearance of something grown beautiful especially with age or use” Merriam-Webster Dictionary.
This word was encountered through “Wind Sand and Stars” by Antoine de Saint-Exupéry.
The sentence the word was used it was “Every machine will gradually take on this patina and lose its identity in its function.”
When the author uses this word he’s trying to say that every machine ages and becomes irrelevant as new technology gets developed. As the machine’s functions get replaced by a better technology people still love the old machines for the purpose they have served at the time that it was first introduced. The author could also be questioning in this sentence why the old is still loved or, trying to argue that humans dislike change even if it’s for the better which is why they choose to admire the old.