Full Idea
Seeing art as expression has two components: 1) if something is a work of art, then it is expressive, 2) if something is expressive, then it is a work of art. So expression can be necessary or sufficient for art. (or both, for Croce and Collingwood).
Gist of Idea
Expression can be either necessary for art, or sufficient for art (or even both)
Source
Gary Kemp (Croce and Collingwood [2012], 1)
Book Reference
'Key Thinkers in Aesthetics', ed/tr. Giovannelli,Alessandro [Continuum 2012], p.101
A Reaction
I take the idea that art 'expresses' the feelings of an artist to be false. Artists are more like actors. Nearly all art has some emotional impact, which is of major importance, but I don't think 'expression' is a very good word for that.