An important part of world history faces an existential threat. Acts of the US government, recordings of indigenous Australians and photographs of English seaside life spanning three decades are just a few of the historical records recorded on acetate films that suffer from irreversible damage due to what is called vinegar syndrome.
Vinegar syndrome occurs when the acetate film is stored in a warm, humid room. These conditions cause the film to decompose. When the film begins to rot, it gives off acetic acid, the same ingredient in household vinegar that gives it its distinctive smell and taste. The acid accelerates the degradation of the affected film and can even damage metal storage containers and other films stored nearby.
Vinegar syndrome cannot be avoided forever, nor can it be reversed. It can only be delayed. That is why archives store their film collections in a cold and dry environment. The film stored under these conditions was expected to last for hundreds of years before vinegar syndrome began to set in. But my colleagues and I have recently shown that these predictions are overconfident and that countless acetate films are threatened with imminent destruction.
Current guidelines suggest that films stored under the same conditions could last around 450 years. For films made in 1950, when acetate films were becoming popular, this implies that vinegar syndrome will not develop until around AD 2400.
But our research predicts that films stored under recommended conditions can last as little as 70 years before developing vinegar syndrome. According to our model, a film made in 1950 and stored under the conditions recommended since then could develop vinegar syndrome this year.
Modeling of film degradation
To understand how film can degrade over long periods of time, scientists perform film experiments at high temperatures and relative humidity. This is called accelerated or artificial aging experiences. Scientists take measurements of a characteristic considered to be a relevant indicator of degradation in the film.
A common measurement is free acidity, which is different from pH. This gives a more sensitive measure of the amount of acetic acid that has built up in the film. Vinegar syndrome is considered to begin when the free acidity reaches a level of 0.5.
By measuring free acidity over time, artificial aging experiments give an idea of how long it takes for the film to develop vinegar syndrome in hot, humid conditions. Scientists can use the results of these experiments to estimate how milder conditions that are more similar to the environment found in the archives will affect the film.
As noted, the acid accelerates degradation in the film, including the chemical reaction that produces the acid in the first place. If the film is stored in a closed container that prevents the acid from escaping (often the case with film frequently stored in metal or plastic cans), this can cause acid levels to increase exponentially over time. time.
In the early stages of degradation, acid levels are low and this tendency is not apparent. This means that in previous studies, the researchers speculated that during the early stages of a film’s life, acidity levels were too low to affect film degradation. Earlier models therefore did not take into account the effect of the acid on the rate of degradation from the start.
A more recent study of the British Library disputed the hypothesis that acid does not influence the degradation of the film from the start. He found no evidence to support that the chemical mechanism changes when the acidity reaches a level of 0.5.
Our study proposed a model to take into account the effect of the acid during the entire degradation process, including the early stages. We used data two studies of the Image Permanence Institute in the United States to develop and validate the model. We then used the model to make predictions about film stability under typical archival conditions. These forecasts were compared to guidelines in the conservation of films.
Acetate films were widely adopted from the 1950s to the 1980s, so it is likely that much of the photographic record from this period is in danger. For example, the BFI Master Collection consists of over 450,000 boxes of film, 59% of which are acetate films. One of the biggest dangers of films with vinegar syndrome is that if not stored properly, the acidic vapors can spread to other films. A single reel of highly degrading acetate film could seriously damage the rest of the collection if vinegar syndrome is not contained.
There are three bases strategies to treat vinegar syndrome:
Improve storage conditions by reducing humidity and lowering temperature.
Quarantine all films identified as having vinegar syndrome to prevent spread.
Duplicate the movie or convert it to digital media.
The damage caused by vinegar syndrome is irreversible and will eventually make the film unrecoverable, so it is best to follow the tips above. Researchers at Queen Mary’s University in London were recently able to retrieve images from a distressed film reel, which was too fragile and fused to unroll, using an x-ray. digitization technique. However, this method would not be possible on a large scale.
Archives use guidelines to plan their film preservation strategy. For large collections, storing the film in cold rooms is much cheaper than copying. If cold storage could really delay vinegar syndrome until midnight, then copying is not urgent. However, the new model predicts that vinegar syndrome will occur much sooner. We may only have a few years, not a few centuries, to act before these films are lost forever.