All about... nitrate film

The bones of celluloid, that magical ribbon which carries our cinematic memories and dreams, are literally that: ground up bones. Made into gelatin – in which microscopic, reactive silver salts are suspended – this emulsion is coated on a clear, flexible, cellulose band a little over a millimetre thick. 

From the 1890s to the 1950s, this ‘film’ was largely what we call nitrate, which though highly flammable was tough enough to survive transport through cameras and projectors. Safety film stocks, which overlapped with and then replaced nitrate, were less clear, and initially more expensive and more breakable.

Aesthetically, nitrate film was unparalleled in its time. Its luminosity and metallic lustre came perhaps from all that silver. It took colour well. From the earliest days, films were offered in hand-coloured, stencilled or tinted and toned prints with a jewel-like quality. Later ‘natural colour’ systems seem flat by comparison, like the difference between a printed picture and a stained glass window.

Nitrate film may have been stronger and more beautiful, but that flammability was a considerable problem. Nitrate fires, such as that of the Paris Bazaar disaster of May 1897, which claimed the lives of 126 people, led to considerable regulation of film projections in many countries. Local by-laws in the UK led to national legislation in 1909. A significant but unintended consequence of this was to give local councils jurisdiction over what films could be screened – essentially the birth of film censorship.

Nitrate film’s propensity to self-combust, shrink and decompose also led to the need to house the film away from the public in temperature-controlled vaults, leading to the establishment of the film archives and the art of film restoration.

Perhaps it was the danger and beauty of it that made it the object of interest to filmmakers themselves. Film’s tendency to reflexivity made the medium itself a recurring subject of fascination, and the subject of nitrate’s volatility occurs in several features, from Michael Powell’s The Love Test (1935), whose hero is working on a flameproof film, to Alfred Hitchcock’s Sabotage (1936), in which a schoolboy is nearly kicked off a bus by the conductor for carrying flammable film against regulations. In a characteristic Hitchcock touch, the cans’ true contents are even more dangerous than nitrate.

The explosion of a can of nitrate film blinds an old projectionist in Cinema Paradiso (1988), while in Inglourious Basterds (2009) nitrate is used for nothing short of bringing down the Third Reich. A documentary film, too, took nitrate as its subject: This Film Is Dangerous, made by the British Navy in 1948. The BFI National Archive has a nitrate print of this film, which illustrates the difficulties of extinguishing nitrate fires.

Even when it decomposes, as all nitrate must, it can still be beautiful, as Bill Morrison’s experimental film Decasia (2002), which comprises sequences of decaying silent films, demonstrates so strikingly.

– Bryony Dixon, curator of silent film, BFI National Archive. 

Nitrate film presents handling and storage complications due to its flammability and, if not kept properly, its unstable chemical form. Nitrate was succeeded by ‘safety’ film stocks with more stable properties, firstly by acetate and then by more modern polyester-based stocks.

As part of our ongoing desire to make our nitrate collections more accessible to the public, a mass system of duplication from nitrate to safety film master stocks was undertaken in the 1980s, and prints were struck from these masters to enable projection in modern cinemas.

Numerous other archives around the world also participated in their own programmes of mass duplication, although for the most part, they then disposed of the nitrate masters due to the high cost of maintaining safe, stable storage.

In the modern era, we can still reproduce nitrate photochemically, but we can also now digitally scan, restore and duplicate nitrate material. Nine early silent Alfred Hitchcock films were restored by the BFI and its partners in 2012 as part of the Hitchcock 9 project, using original nitrate material where it was still available, and digitally scanning and restoring the intertitles. They were then printed on modern safety stocks for exhibition, as well as being released digitally. Many other examples of digital restoration of nitrate material can be found on BFI Player, the BFI Youtube channel and in the BFI Mediatheque. 

Even after duplication, we still retain the majority of our own nitrate masters. When not being accessed by our conservation teams at the BFI National Film Archive’s J P Getty Jr Conservation Centre, these films are kept at our purpose-built Master Film Store (MFS) in Warwickshire, which opened in 2012 and celebrates its 10th anniversary this year.            

The MFS sustains a deep storage temperature of -5°C, and 35% relative humidity (RH). This cold and dry environment maintains stasis of a film’s current condition, as well as greatly slowing any decomposition over many decades. 

Film stored in the MFS must go through an acclimatisation process, where it is gradually brought up to room temperature over a period of 24 hours before it can be worked on by our technical staff. This slow bringing-up-to-temperature reduces dew point formation and prevents condensation on the film roll.

Film is then transported in accordance with best practice from the MFS in a Thermacoolie (an insulated polystyrene box) via a refrigerated van, and stored in a local environmentally controlled vault at the Conservation Centre until any work on it is completed. Then it is returned to the MFS for continued deep storage.

Nitrate film is dangerous when not stored or handled correctly, and our archivists are trained in nitrate handling technique to mitigate this risk. You should never handle nitrate film unless you are trained to do so. If a member of the public should discover any nitrate film in their own collections, please contact the BFI for safe storage and handling guidance.

Nitrate will deteriorate over time unless stored in correct conditions, but the reason why nitrate’s danger is so fascinating is its self-destructive property when it burns. Burning cellulose nitrate produces oxygen as a by-product, which is one of the three key parts of the combustion fire triangle (heat, fuel, oxidising agent).

Simply put, once alight, it is incredibly difficult, if not impossible, to extinguish until it has burnt itself out and no film (fuel) remains. One burning poundweight of cellulose nitrate can reach temperatures of around 4,444°C, and is 15 times more combustible than a similar weight in wood. This heat, combined with the production of toxic gases from the combustion process, can present an immediate threat to life.

Nitrate fires accounted for the losses of numerous cinemas and theatres in the first half of the 20th century, often caused by improper handling and negligence, but these events tailed off with the acceptance of ‘safety’ stocks becoming standard.

The BFI is currently the only UK organisation to be licensed to project nitrate film stock, and there have been several hugely popular seasons of nitrate film screenings at BFI Southbank. With proper care and storage conditions, nitrate stock can endure for many years, and we hope to continue to preserve and make accessible the nation’s nitrate collection for many years to come.

– Louise Allum, Jo Molyneux and Kieron Webb, BFI National Archive

Bearing in mind how flammable nitrate film is, running it past a 4500W focused Xenon light seems like foolishness. Any break in the film as it passes through the gate assembly is liable to cause an instant conflagration. Of course, nitrate film has been projected safely for over a hundred years, but due to its age – all nitrate film is at least 70 years old – and its potential for decomposition, great caution must be observed.

Even before it reaches the cinema, any nitrate print must be carefully checked to ensure minimal shrinkage and damage is present. Once it arrives the print is stored at low temperature and only few reels are permitted in the projection booth at any time. The projectionist will check the integrity of the print again, ensuring that any splices are well made and secure, and that any damaged perforations are repaired. Ideally there will be very few per print.

Once ‘made up’ the nitrate print is laced on the projector. Due to nitrate’s history of lethal fires, any projector designed for nitrate projection will have certain safety features honed over the years. The top and bottom spoolboxes and projector head will be enclosed with metal doors so as little of the print as possible is exposed to the air. Safety shutters are installed that only allow light to pass once the motor is at full speed, and the rest time of each frame in the projector gate is at ½4of a second.

In later decades fire suppression equipment was installed on projectors with a gun cotton trigger that instantly fired canisters of CO2 over the whole of the projector if a frame caught fire. More recent upgrades in NFT1 – the main screen at BFI Southbank – use Novec gas and heat sensitive tubing to set off the permanently pressurised system as well as the reliable gun cotton above the gate. Finally, there are safety shutters that are triggered as soon as any fire is detected, ensuring that the glass portholes are protected.

When built in 1957, the projection booth in NFT1 was entirely encased in encapsulated asbestos. It still is, making it very safe from the effects of fire but difficult to update. This design helped protect the building during a nitrate fire in 1968, which was caused by an undetected nitrate print being run without safety features in place.

The best way to avoid a fire is careful make up and careful projection so no breakages happen. Each nitrate print is run without the lamp first to ensure it runs smoothly. Then it can be projected to the public. It is a great and rare privilege to be able to forge that link with the projectionists of the past and still be able to show this unique and beautiful format to an audience.

– Dominic Simmons, BFI head of technical services

The BFI Reuben Library contains a huge spectrum of written material about the moving image. The library was formed in 1934 and contains materials dating from pre-cinema times all the way up to full text articles available electronically in the Edwin Fox Foundation reading room. 

Visitors can start learning about nitrate from several key texts held in the collection, such as Michael Binder’s ‘A Light Affliction: A History of Film Preservation and Restoration’ (2014) and ‘This Film Is Dangerous’ edited by Roger Smither and Catherine A. Surowiec (2002). 

The writings of Italian film curator and historian Paolo Cherchi Usai are also a good place to start when researching nitrate film as a physical medium. The Italian film historian and curator has written and contributed to a large number of books on the subject, some published by the BFI, and we hold more than 30 of these titles in our collection. You can also find a vast number of articles in many different journals on the subject of film history, silent cinema and film preservation that he has written over the years. 

In the reading room at BFI Southbank you can freely consult our sequence of Kinematograph Year Books dating from 1914. Within the pages, you can read about legal judgements against cinemas that flippantly disregarded the well-being of their workforce and customers, and the enforcement of the New Celluloid Act of 1922. This act restricted cinemas, which were predominantly wooden, to holding a maximum of 20 reels or 80lbs of nitrate film. These were to be stored in individual metal cases, with only three reels allowed in the projection booth at one time.

The library itself has four books in its collection that contain samples of actual nitrate film. These are, of course, not kept on the shelves among the rest of the stock to be freely accessed, but squirrelled away in the BFI National Archive at Berkhamsted in a metal box among cans of film stock.

Library materials held off site at Berkhamsted include many fascinating and often delicate treasures, such as manuals and handbooks for projectionists from the time of nitrate film production and exhibition. The Cinematograph Book of 1925 contains a whole chapter dedicated to fire prevention in cinemas projecting nitrate, insisting that the first rule was “to keep cool”; furthermore, such behaviour would be the difference between a well-trained operator and a “mere handle-turner”. This may sound scathing, but it was gentler than Johnson’s 1925 edition of Motion Picture Theatre Electrical Equipment & Projection, who simply entitled a chapter: ‘Don’t’. 

– Victoria Crabbe and Eleanor Watkins, BFI Reuben Library

The inaugural BFI Film on Film Festival will take place from 8 to 11 June 2023.