“You know, I've never played slide before, but it just started doing things on its own – I didn’t even have to try”: That time Paul McCartney channeled his inner bluesman – with the help of Nirvana, and a wild 4-string cigar box guitar

On the surface, you wouldn't think Nirvana – with their anarchic live performances, and the crunchy distortion and blistering volume of their studio recordings – had much in common with the Beatles.

The Fab Four, however, were a major influence on Nirvana's frontman and electric guitar player, Kurt Cobain, from his childhood through his development of Nirvana's world-altering catalog.

“I remember years ago asking [Cobain's hometown friend] Eric Shillinger, ‘How successful do you think a band could be if they mixed really heavy Black Sabbath with the Beatles?,” Cobain once recalled to journalist Michael Azerrad. “What could you do with that?”

If only Cobain could've seen – decades later, and almost 20 years after his tragic death in 1994 – all three of his Nirvana bandmates create, and perform, an original song with Paul McCartney.

2012 was an especially unlikely time for McCartney to join forces with the grunge legends, fresh as he was off the back of that year's Kisses on the Bottom, a stately album that saw the Mount-Rushmore-of-pop songwriter tackle standards of the '30s, '40s, and '50s – a far cry from Territorial Pissings, for sure.

And yet, 2012 was also the year that saw McCartney, Dave Grohl, Pat Smear, and Krist Novoselic create Cut Me Some Slack, a blues-grunge howler that featured McCartney riffing – and even, for the first time, showing his slide guitar skills – on one of the strangest guitars he's ever slung over his shoulder.

McCartney first played Cut Me Some Slack – a studio version of which would be released on the 2013 Grohl-led Sound City: Real to Reel album – live at the 12-12-12 Hurricane Sandy relief benefit concert at Madison Square Garden.

His mini-set was loaded with Beatles, Wings, and solo classics, for which McCartney – among other instruments – used a couple Gibson Les Pauls, and, of course, his trademark Hofner bass guitar.

For Cut Me Some Slack, though, McCartney was armed with a “Resofiddle,“ a “paint can lid resonator“ cigar box guitar built by Matty Baratto, a luthier whose incredible clientele list includes – aside from McCartney – Prince, Josh Homme, Joe Perry, Jack White, Slash, Keith Richards, Zakk Wylde, and Johnny Depp, among many others.

According to Baratto, it was Depp who got the Resofiddle (and a Baratto wine box guitar amp, featuring a 6” Jensen speaker, to go with it) into the Beatle's hands. As soon as McCartney picked it up, it led his playing in entirely new, and fascinating, directions.

In an interview with Guitar World, Baratto recounted meeting McCartney, and the latter's wonder at the Resofiddle, and where it took him, artistically.

“You know, I've never played slide before, but it just started doing things on its own,” the Beatle told Baratto. “I didn’t even have to try, the sound... it just did things.“

“As a guitar maker,” Baratto tells Guitar World, “you don’t really need much more of an endorsement.”

“I never, in a million years, would have thought that I’d [one day] be talking about Resofiddles one-on-one with one of the most influential musicians ever,” Baratto says. “But there I was, listening and feeling like I was watching from above in a dream state – just hoping to remember everything.”

Baratto – who, before starting his own company, cut his teeth at Ibanez's LA Custom Shop from 1994 through 1999 – outfitted his four-string (tuned D, A, D, F#) Resofiddle with a lipstick pickup and brass nut.

Just days after the 12-12-12 concert, the Resofiddle (examples of which would eventually go on display at the Grammy Museum, after Cut Me Some Slack picked up the 2014 Grammy for Best Rock Song) made another prominent appearance during McCartney and Nirvana's performance of Cut Me Some Slack on Saturday Night Live.

The considerably more intimate SNL stage allows for some killer, up-close looks at the cigar box four-string, particularly its beautifully retro body.

Baratto says that he told McCartney, “I always wanted to be on SNL.” To that, the Beatle smiled, playfully hit the luthier on the shoulder, and said, “You were all over it, man!”