Painting style in my opinion encapsulates history (7)
I believe the answer is:
impasto
'painting style' is the definition.
(impasto is a painting technique)
'in my opinion encapsulates history' is the wordplay.
'in my opinion' becomes 'imo' (common abbreviation).
'encapsulates' indicates putting letters inside.
'history' becomes 'past' (I've seen this before).
'imo' placed around 'past' is 'IMPASTO'.
(Other definitions for impasto that I've seen before include "Art technique of laying paint on thickly" , "Good covering of paint" , "Style of painting" , "application of paint in this way" , "Thickly-applied paint" .)