Round metal boxes, stored from floor to ceiling. In these humidity-controlled rooms near Los Angeles, a handful of specialists work to preserve a million reels which constitute the precious and fragile memory of Hollywood.

While the stars of the moment are climbing the steps in Cannes, little hands on the other side of the world are waging a battle against time in the shadows: saving miles of film of original masterpieces for the big studios. work of American cinema. The big fear is the so-called vinegar syndrome, the degradation of the acetate film into acetic acid, which “prevents it from being used”, explains Tim Knapp, manager at the specialist company Pro- Tek Vaults.

Because what is today watched almost exclusively in digital version was done, from the birth of cinema until recently, via unstable materials. At the dawn of the moving image was nitrate film. Deep black, shades of gray, strong contrast, this technique was that of Charlie Chaplin, Buster Keaton and other founding fathers. But nitrate is flammable, very flammable. So many fires broke out in cinemas that projection rooms were fireproofed.

Even storing it is like playing with fire. In 1914, a treasure trove of archives from the early years of American cinema was reduced to ashes in a huge blaze. At the beginning of the 1950s, the arrival of acetate film was welcomed by the entire film industry: finally a material that captured quality images without it catching fire. But hidden in this long-awaited innovation is a time bomb. If poorly preserved, a reel can, in fifteen years, transform into a common piece of plastic with an unreadable smell of vinegar.

It is to avoid the ruin of archives – original works known as forgotten nuggets – that Pro-Tek Vaults and other specialists so delicately control the temperature and humidity level of their storage rooms. “This allows us to keep copies as best as possible, often originals, which can be used to make copies or be digitized over time,” explains the boss, Doug Sylvester. And at a time when the giants of the sector are trying to extract more revenue from old titles in their catalog, between rebroadcasting and sales to streaming platforms, safeguarding their heritage has become even more crucial. Added to this is the persistence of the film. If the vast majority of current filming is done with digital cameras, a handful of diehards among directors stick to this technique which does not confine the light to a defined number of pixels. Christopher Nolan shot his multi-award-winning Oppenheimer on film.

In the conservation rooms of Pro-Tek Vaults are stored thousands of hours of feature films, but also television shows, presidential archives and even music videos. In total, half a million kilometers of film, video-monitored in hangars in Burbank and Thousand Oaks, north of Los Angeles. The challenge is not to have the original negatives of a major film stolen. Which ones are jealously guarded in the vaults? Doug Sylvester and his company remain discreet on this subject. A clue perhaps: on their walls, posters of West Side Story or Back to the Future 2. “For safety, (our customers) prefer that we remain vague,” specifies Doug Sylvester. “I can tell you that there are some of the great classics,” he says. “If you look at the American Film Institute’s list of the 100 greatest films, many of them are in our inventory.”

In addition to preserving treasures locked in this fragile acetate, the employees carry out painstaking work: the inventory and digitization of works, sometimes unknown to their owner. They thus brought out previously unseen images of a Guns N’ Roses concert for Universal music and restored video clips of Johnny Cash, Bon Jovi and the Cranberries. Finding these pearls is a joy for Doug Sylvester. “It’s part of our cultural history, and we look forward to participating in its preservation for the future.”