Painting is dry and firm (5)
I believe the answer is:
secco
'painting' is the definition.
(I've seen this before)
'dry and firm' is the wordplay.
'dry' becomes 'sec' (similar in meaning).
'and' is a charade indicator (letters next to each other).
'firm' becomes 'co' (abbreviation for company).
'sec'+'co'='SECCO'
'is' acts as a link.
(Other definitions for secco that I've seen before include "Painting technique on dry plaster" , "Dry (of wine)" , "unaccompanied?" .)