“eaten out with acid”

But it proceeds from the material, the material eaten out with acid, pulled down from underneath, made to perform and always kept in order, in its place. Sometimes it cannot be made to indicate its spiritual goal clearly (…) but even then the spiritual must be felt. Miss Moore does this – but occasionally, I think, the super-material content of the poems is too easy for the material involved – it could have meant more…Genuine religious poetry seems to be about as far as poetry can go – and as good as it can be.

- from Elizabeth Bishop’s notebooks (quoted in David Kalstone’s study of Bishop, Moore and Lowell)