Full Idea
A statue is not identical with its constituent lump of clay because they have different persistence conditions; the statue, but not the lump, could survive the loss of a few smallish bits, and the lump, but not the statue, could survive being squashed.
Gist of Idea
Clay does not 'constitute' a statue, as they have different persistence conditions (flaking, squashing)
Source
Trenton Merricks (Objects and Persons [2003], §2.III)
Book Reference
Merricks,Trenton: 'Objects and Persons' [OUP 2003], p.38
A Reaction
I don't see why a lump can't survive losing a few bits (if the lump never had a precise identity), but it is hard to argue that squashing is a problem. However, presumably the identity (or constitution) between lump and statue is not a necessity.