Film collector, curator and historian Fernando Pena figured he’d made the biggest discovery of his career when, back in 2008, he uncovered a complete print of the original, uncut version of Fritz Lang’s “Metropolis.” The 1927 German expressionist sci-fi epic had been gathering dust in the archives of Argentina’s national Museo del Cine. But one month ago, Pena topped himself when he happened upon an equally remarkable gem: an alternate cut of Buster Keaton’s “The Blacksmith.” If “Metropolis” was Pena’s Holy Grail of lost film finds, count “The Blacksmith” as his Shroud of Turin.

One of the many two-reelers Keaton made for producer Joseph M. Schenck, the 1922 film stars the silent comic as a hapless small-town iron forger, and includes such signature gags as Keaton doing battle with a giant overhead magnet, destroying a pristine Rolls Royce in the course of fixing a tire, and getting his foot stuck in the path of a speeding locomotive. In the version discovered by Pena, half of the film’s first reel (approximately 5-6 minutes of screen time) consists of entirely different, never-before-seen Keaton gags, while the ending of the film also differs slightly.

Because it was common practice in the silent era for films to be shot with two cameras placed next to one another, resulting in two separate negatives — one for domestic prints and one for foreign export — various alternate versions of silent films have surfaced through the decades. (A print of Keaton’s own 1928 feature “Steamboat Bill Jr.” containing noticeably different takes and camera positions was discovered in 2010.)

But “The Blacksmith” is a special case because the two versions of the film vary so wildly.

Pena made the find while examining a lot of 9.5mm film prints purchased on eBay in 2008 by his friend and fellow collector Fabio Manes. Originally developed in 1922 by the Pathe company in France, the 9.5mm gauge went on to become a popular home-viewing format throughout Europe. The print of “The Blacksmith” contains French intertitles. In theory, this means that all 9.5mm European prints of “The Blacksmith” could feature the alternate footage, but until now nobody noticed.

As with the uncut “Metropolis,” which had languished undetected for decades as it was moved around from archive to archive, Pena notes, “It’s something that has always been there, but no one was looking for it.”

Most notably, the extended gag sequence in which Keaton accidentally sprays oil all over one side of a beautiful white mare is missing from the Pena/Manes print, replaced by a sequence of Keaton leaving the smithy and driving through town, where he runs over his harried boss (frequent Keaton foil Joe Roberts), followed by a madcap pursuit. Also included is a brief additional interlude between Keaton and leading lady Virginia Fox.

So far, Pena has shared his discovery with noted film historians John Bengtson and Kevin Brownlow, the latter of whom wrote in an email to Pena: “I have not seen European releases of American films which differ in any more than the odd shot, extra title or varying camera angle. Half a reel is unprecedented.” The next step, Pena says, is “to get the film restored and made available again to audiences — where it belongs.”