The Alchemy Index is Thrice's fifth studio recording, a four-disc concept album that was split between two releases, the first in October 2007 and the second in April 2008. The band originally planned to release four discs at once, each disc with six tracks representing one of the four classical elements: Fire, Water, Earth, and Air. The album was recorded from late 2006 to early 2007, and a blog titled The Alchemy Index chronicled the album's progress for fans.