He's talking about a recent discovery that helped bring a film from the 1920s back to its original form, a restored version he will be showing to Australian audiences. Writer and critic Kehr will be in Australia for an international archivists conference in Sydney. He will also be introducing a session at Melbourne's Cinematheque, showing two recent restorations carried out at New York's Museum of Modern Art (MOMA), where he is a curator in the film department.

Sometimes miracles can be on a larger scale, when prints of movies thought to have been lost forever are found, whether by chance or as a result of painstaking detective work.  But we will only recover a fraction of what has disappeared. The Library of Congress recently put out a report estimating that only 14 per cent of silent films released by major studios survive in their original 35mm or other format. Another 11 per cent are in foreign versions or on formats of lesser image quality. "Discoveries are being made all the time," Kehr says, "but they will never make up for the 75 per cent that's just vanished."

One of the films screening at the Cinematheque is The Iron Mask (1929), directed by the prolific Allan Dwan, an innovative filmmaker Kehr rates as "second only to D. W. Griffith in the development of the narrative film in the United States".

It is based on Alexandre Dumas' tales of The Three Musketeers, and it has many elements of transformation and farewell. It was one of the last major roles of the silent star Douglas Fairbanks Sr, and it was made on the cusp of the sound era.  Part way into production, as the filmmakers saw the success of the new "talking pictures", they decided to add a music and sound effects track, as well as three passages in which Fairbanks could be heard speaking.

These sound elements were lost until recently, when a collector in California found the original discs for the Vitaphone process. They matched up with the original negative that Fairbanks himself had given MOMA in the 1930s.

This relatively straightforward restoration "brings the film back to pretty much what people saw and heard when they went to the film in 1929", Kehr says. The sound was cleaned up a little, but "it's not tricked up to sound like a contemporary movie. When you do restoration work, you try to get as close as possible to what the filmmaker intended – of course, while using modern digital technology and restoration techniques".

The other restored film he is screening is Raoul Walsh's Wild Girl, 1932, "which was acquired by the museum when 20th Century Fox decided that they were going to throw away all their old nitrate prints back in the Seventies".

One of MOMA's current restoration projects is Rosita (1923),  the American debut of the great German director Ernst Lubitsch, who went on to have a long career in Hollywood. The film was a critical and commercial hit, but its star, Mary Pickford, turned against it "for reasons that are still mysterious to me, after all the research I've done," Kehr says. She was a good archivist of her own films, but the print of Rosita was the only one that she allowed to disintegrate.

What appears to be the only surviving print was found in the Moscow Film Archives in the 1970s. It has Russian intertitles: one of the next tasks for MOMA will be to reconstruct the intertitles, using, among other things, Russian, German and Swedish sources, and an incomplete music cue sheet.

MOMA's film archive was founded in 1935, and is the oldest in the world. A visionary British critic and curator, Iris Barry, was its first curator, and she amassed a remarkable collection of prints. It is nevertheless a relatively small archive compared to the Library of Congress and the UCLA Film &Television Archive, Kehr says. It has the resources to work on around 10 restoration projects a year.  "We have to raise separate funding for each one, so there are lot of different priorities, and tough choices to be made", often taking into account matters such as urgency and overall cost.  And priorities aren't always obvious. "One of the things you learn as an archivist is that if it's not to your taste, it doesn't mean that someone in 10, 20 or 30 years from now won't find it interesting."

At the same time, he worries about the audiences for some of the films MOMA has in its collection. "More and more we are going to be the monks in the Dark Ages for the next little while," he says. It seems to him that there is a waning interest in what is regarded as the classic period of Hollywood filmmaking. His cut-off point for this is around 1980, when directors from that earlier period were making their final movies and the new generation of Coppola and Scorsese had "fundamentally changed the aesthetic of American film".

He doesn't understand why people have lost interest in the precursors of the new generation. "I'm really kind of amazed that it all changed so quickly," he says, so that when he gives talks at universities, there are often students who don't know who Howard Hawks is, or even Humphrey Bogart. But he's also clear about the archivist's mission. "We have to hold on, protect, and wait for it to be discovered again."

The Iron Mask and Wild Girl screen at the Melbourne Cinematheque at the Australian Centre for the Moving Image on Wednesday, April 22. The Iron Mask screens in Sydney at the AFTRs Theatre, in the Entertainment Quarter at Moore Park, on Thursday, April 23. Dave  Kehr will speak at both screenings.

melbournecinematheque.org