Paint sprayed on a surface layer (6)
I believe the answer is:
patina
'surface layer' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'paint sprayed on a' is the wordplay.
'sprayed' indicates anagramming the letters (I've seen this in other clues).
'on' indicates putting letters inside (as in clothing 'on' a person).
'paint' anagrammed gives 'ptina'.
'ptina' placed around 'a' is 'PATINA'.
Can you help me to learn more?
(Other definitions for patina that I've seen before include "Distinctive surface acquired over time" , "Surface film formed by age" , "Fine layer on the surface, laid down over time" , "Green gloss on old bronze" , "thin coating" .)