Firm supporting a lot of recent painting (6)
I believe the answer is:
fresco
'painting' is the definition.
(fresco is a kind of painting)
'firm supporting a lot of recent' is the wordplay.
'firm' becomes 'co' (a firm is a company).
'supporting' says to put letters next to each other (in a down clue, some letters go below others).
'a lot of' means to remove the last letter (most of the word but not all of it).
'recent' becomes 'fresh' (fresh can mean current or new).
'fresh' with its final letter taken away is 'fres'.
'co' after 'fres' is 'FRESCO'.
(Other definitions for fresco that I've seen before include "Mode of wall painting" , "Watercolour done on wet plaster" , "Picture painted on wet plaster" , "Painting done in wet plaster" , "Wall-painting" .)