Eric Clapton is a man hidden from view in Showtime’s dull ‘Life in 12 Bars’

Aging rock stars in long-look-back mode often describe their first guitar or their first piece of vinyl with near-mythic language, as though they were recounting pulling a sword from a stone.

Not Eric Clapton.

“Obviously, when I got to the age to buy records, I went and bought them,” the singer and guitarist, now 72, recalls in “Eric Clapton: Life in 12 Bars,” a new documentary set to air Saturday night on Showtime after premiering last year at the Toronto International Film Festival.

The dry-as-toast quote is typical of rock’s most dispassionate public figure — and indicates filmmaker Lili Fini Zanuck’s challenge here, which is to tell a compelling two-hour story from the point of view of a guy who’s never seemed at all eager to let anyone inside his head.

It’s not that Clapton’s life has lacked drama, as anyone who’s heard his anguished howl in “Layla” can be sure.

Zanuck, an Oscar- and Emmy-winning producer who’s known Clapton since she hired him to score her 1991 movie “Rush,” anchors “Life in 12 Bars” in three traumatic episodes: Clapton’s abandonment as a boy by his mother, his obsession with the model and photographer Pattie Boyd (who was married at the time of his infatuation to Clapton’s best friend, George Harrison) and the death of his 4-year-old son, Conor.

Clearly, that early rejection is what drove Clapton to develop his ability as a guitarist, first as a member of the Yardbirds and John Mayall’s Bluesbreakers and then with Cream, and Derek and the Dominos and on his own as a solo act.

And the later ordeals are what provided Clapton with the raw material for some of his best-known songs, including “Layla,” which he famously wrote in the hopes of winning over Boyd, and “Tears in Heaven,” about an imagined reunion with the small child who died after falling from the 53rd floor of a New York apartment building.

Yet Clapton simply hasn’t anything profound or insightful to say about these episodes that you don’t already get from his music. Or at least he wasn’t willing to say it to Zanuck, who relies as much on archival footage as on fresh interviews with Clapton, Boyd and other players in his life.

That reticence is unlikely to surprise anyone who’s followed Clapton’s career in recent years. Headlining the Forum in September (as part of a brief tour he’s suggested will be his last), he looked like his goal was getting through the show without adding any fresh wrinkles to his legacy.

But then why agree to take part in this film, for which he’s almost certainly earning less than from those $500-a-seat gigs?

Zanuck wasn’t helped by her decision to forgo the talking head approach and use Clapton’s often-dull commentary as voice-over to accompany old photos and video.

If his words don’t illuminate much, perhaps we could’ve learned something from watching him speak.

What “Life in 12 Bars” has going for it is Clapton’s music, which it features plenty of. There’s a detailed account of the early-’70s “Layla” sessions, for instance, that digs into Duane Allman’s role in the song; it’s a thrill to hear his isolated slide-guitar track in all its crazy, yelping glory.

And hard-core fans will relish a few minutes of vintage film showing a twentysomething Clapton in the studio with Aretha Franklin.

But the sight of that fiery young gun only makes Zanuck’s subject seem colder to the touch today.

‘Eric Clapton: Life in 12 Bars’

Where: Showtime

When: 9 and 11:15 p.m. Saturday