So, I started digging away online, having to work from English.

I was surprised at what I found.
Granted, no citations or bibliography, but something more to work with.

"Art is not a mirror, but a hammer.
It does not reflect, it shapes!
The poem, the song, the picture
is only water drawn from
the well of the people
and it should be given back to them
in a cup of beauty
so that they may drink, and, in drinking,
understand themselves."

The place where this is printed is
a 1984 publication called Theatre Profiles
which can only be viewed, at Google Books, in 'snippet' form.

But just look at those first two lines:
it might be easier to scare something up using those,
especially if you go to Spanish rather than English.

When Garcia Lorca says "hammer"
I interpret this as a sculptor, like Michelangelo,
with hammer and chisel.