In 2012, a large wooden crate containing hundreds of artworks by Swedish artist and mystic Hilma af Klint was delivered to the office of Daniel Birnbaum at the Moderna Museet in Stockholm. This was only a small portion of the secret artworks—never exhibited, much less properly documented—left behind when the artist died in 1944 at the age of eighty-one. For Artforum’s January 2013 issue, Birnbaum illuminated af Klint’s enigmatic oeuvre in an essay that, like the artist’s work, raises more questions than it answers: Is af Klint the first modern abstract artist? Are we ready to recei...