Pottery cracking in wall (7)
I believe the answer is:
faience
'pottery' is the definition.
(faience is a type of ceramic)
'cracking in wall' is the wordplay.
'cracking' becomes 'AI' (resembles A1, informal term for excellent).
'in' is an insertion indicator.
'wall' becomes 'fence' (synonyms).
'ai' placed inside 'fence' is 'FAIENCE'.
(Other definitions for faience that I've seen before include "porcelain" , "ceramic ware" , "A glazed earthenware" .)