Frank Zappa is often regarded as one of the most brilliant, idiosyncratic musicians in rock music. But looking back at his eclectic, monstrous body of work as a composer, guitarist, vocalist and bandleader, Zappa really wasn't a "rock" musician. That fact is cemented on Lumpy Gravy, Zappa's first solo album, which was officially released on May 13, 1968.

It's a sadly overlooked item in the Zappa oeuvre, probably because – even for Zappa's standards – it's so damn weird, branching from musique concrete to gorgeous jazz-fusion to proto-electronic hysteria to pitch-shifted rock grooves. Composed in a jaw-dropping eleven days (and featuring the warped talents of the "Abnuceals Emuukha Electric Symphony Orchestra"), the album was envisioned as one chunk of a four-album project called No Commercial Potential (also including 1968's We're Only in It for the Money, 1968's Cruising With Ruben & the Jets and 1969's Uncle Meat).

Taken on its own, Lumpy Gravy makes little sense – musically or lyrically – but its lack of logic and coherence is its most brilliant virtue. Building on the chaotic template he established on his first two albums with the Mothers of Invention (especially their debut, 1966's Freak Out), Lumpy Gravy turned out to be an avant-garde masterpiece.

The individual "songs" are hardly songs at all. Each mini-movement flickers in for a minute or two and disintegrates – the overall experience is like flipping through radio stations beamed in from another planet. The album is divided into two nearly-sixteen-minute halves, both crammed with highlights, from a lush early instrumental version of future live staple "King Kong" to the nimble spy-theme parody "Duodenum." The second half is a bit tougher to digest with a clear head – particular the opening four minutes, which feature satiric hippie-mystic ramblings on ponies, paranoia, and the boogie man.

Recording the album was Zappa's first real experience dealing with a proper orchestra, and some of the experiences weren't pleasant. Zappa often faced strong skepticism from the players, who scoffed at his bizarre writing methods.

"Most studio players get paid by the whole note, by the pound for chordal backgrounds for singers." said Zappa in a 1983 interview with Mix. They don't want to sweat. I mean, the hardest thing in Lumpy Gravy was this one section where everybody had to play in 5/8. In 1966 when that session took place, you never saw anybody hand you a piece of music in 5/8. It just wasn't done. But with the proper amount of rehearsal, there are guys who can play the stuff."

Lumpy Gravy had a sizable influence on both rock and avant-garde artists over the years: Captain Beefheart's Trout Mask Replica, released only one year later, takes a similarly chaotic approach. But equally telling is that Zappa himself regarded it as one of his masterworks.

"For him, every album was just part of the same composition and everything was all one big piece of music," said Zappa's wife Gail in a 2008 interview with Vanity Fair. "But the three particular pieces that he considered his absolute masterwork were Lumpy Gravy, We’re Only in It for the Money and Civilization Phase 3."

See Frank Zappa Among the Top 100 Albums of the '60s

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