For the past 20 or so years, Russell Mills has been at the heart of England's avant-garde and experimental scenes, where musicians intersect with visual artists and visual artists often end up as musicians. Though perhaps best known for his album covers—Nine Inch Nails' rust- and decay-adorned The Downward Spiral is perhaps most recognizable to Americans, though he's also decorated discs by Bill Laswell, David Sylvian, Brian Eno, Cocteau Twins, Robert Fripp, and many others—Mills has recently begun to release albums of his own under the name Undark. Mills obviously knows a few people, and he's called in some favors for Pearl + Umbra. Soliciting sonic scraps, works in progress, and otherwise discarded elements of songs from many of his famous friends, Mills and trusty engineer Tom Smyth have created a multi-layered soundscape that's not unlike his immediately recognizable organic art works. Pearl + Umbra is like a game of spot-the-contributor, made all the more difficult by the sheer number of familiar names. Just a few of the generous donors of time and sound: Robin Guthrie, Michael Brook, Harold Budd, Brian Eno, Roger Eno, Peter Gabriel, Bill Laswell, Graham Lewis, Ian McCulloch, Thurston Moore, David Sylvian, and Hector Zazou. If any or all of these names sound familiar, chances are you'll find Mills' ambient drifts and sculpted fragments both fascinating and compelling.