What is Nitrate Film?
Nitrate film is a type of film stock with a cellulose nitrate base. Cellulose nitrate, also known as nitrate and nitratecellulose, is a transparent plastic. From the 1890s to 1952, commercial 35mm film (used for motion pictures) was made of nitrate. There’s one major problem, though. Nitrate is highly flammable and can spontaneously combust.
Let’s talk about film structure for a hot second. All film stock has two primary layers. The first is the base, a thick layer of transparent plastic providing support. This is the cellulose nitrate, or later, cellulose acetate. Then we have a thin layer called emulsion, which carries the photosensitive materials in a gelatin binder. The emulsion is where the images are.
When motion picture film came into being in the 1890s, nitrate was the only available plastic strong and flexible enough for movie cameras and projectors. Never mind that it can be dangerous…we’ve got movies to make!
Nitrate Film Manufacture
Over time, the film industry realized it shouldn’t continue using nitrate because of its potentially disastrous effects. In 1948, the Eastman Kodak Company started phasing out cellulose nitrate and used cellulose acetate (safety film) instead. It took about four years to stop using nitrate. While most sources say 1951 was the last year of manufacture, Kodak says they finally discontinued it in 1952.1
Identifying Nitrate Film
Since cellulose nitrate is highly flammable, it was never used for 16mm or 8mm film. Because amateurs and hobbyists used these smaller film gauges, they were made with safety film. Kodak never sold nitrate film on the home market.
So, how do you know if you’re dealing with nitrate? Well, if it’s 35mm gauge, a commercial film, and has “NITRATE FILM” on the edge, you’re fucked. Not all nitrate film stock has this identifier, though.
If the roll of film in grandma’s attic is a home video, 28mm, 16mm, 9.5mm, Regular 8mm, or Super 8mm, and it says “SAFETY FILM” on the edge, the base is cellulose acetate, and you’re safe.
You can also identify nitrate or safety film by date and signs of decay. Safety film has what we call vinegar syndrome because it, well, smells like vinegar when it deteriorates. See below for signs of nitrate decay.
Does Nitrate Really Explode?
Nitrate film is flammable AF and can self-combust. A nitrate fire is almost impossible to extinguish. It burns hot and fast. When nitrate ignites, it produces oxygen. That oxygen feeds the flames, so the fire keeps going and going and going… Nitrate also releases noxious fumes that are dangerous to humans and nearby collections.
You may be wondering if nitrate film bursts into flames willy-nilly. The answer is no…not really. There has to be a set of conditions in place for cellulose nitrate to self-combust.
In a nutshell, nitrate goes kaboom when it decays and is in a high-temperature environment.
Nitrate Decay
Cellulose nitrate has inherent vulnerabilities that cause a chemical process of decay. This process speeds up when nitrate isn’t stored properly. Deterioration can’t be reversed, but improved storage conditions slow it down. In good environmental conditions, nitrate has a pretty good shelf life.
According to the National Film Preservation Foundation, there are 5 stages of nitrate decay.2
- The image fades, there’s a brownish discoloration of the emulsion, and a faint noxious odor emerges.
- The emulsion becomes sticky, and there’s a faint, noxious odor.
- The emulsion softens and blisters with gas bubbles. The odor is more pungent. Once the film reaches this stage, it can’t be duplicated because the image is lost. At this point, the film is hazardous waste and must be disposed of by an authorized facility. You can’t just throw it out in the trash.
- The film congeals into a solid mass with a strong, noxious odor.
- The film disintegrates into brownish powder.
Image 1: Decomposing Nitrate Film, Library of Congress, CC BY 3.0, via Wikimedia Commons; Image 2: Photograph No. 64-NAD-147; “Sample of Deteriorated Motion Picture Film Found at the White House Garage,” January 17, 19363; Image 3: Photograph No.64-ND-3931; “Deteriorated Nitrate Base Motion Picture Film,” 19694; Image 4: Nitrate Film Decay from the EYE Film Institute Netherlands, Hansmuller, CC BY-SA 4.0, via Wikimedia Commons; Image 5: Photograph No. 64-NA-1-493; “Deteriorated Motion Picture Film (Nitrate) in Bubbling Foam Showing Deterioration of Acetate Core,” July 11, 19495.
Nitrate Go Boom
As nitrate decays, it releases gases, including nitric oxide and nitrogen dioxide. If stored in a film can, the decaying cellulose nitrate base makes a sort of pressure cooker. If the gases can’t escape the can, heat builds up, and the nitrate explodes. This also happens if nitrate is stored in an airtight vault – there will probably be an explosion.
If nitrate is just chilling on a shelf, but the temperature and humidity in the storage environment are high, it’ll spontaneously ignite. All you need is a really hot day…
The more decayed the nitrate, the easier it ignites.
Discovering Nitrate Film: An Archivist’s Nightmare
As an archivist, I’ve discovered many cool objects hidden in collections.
One day, I opened a box and found two rolls of film. One of them was 35 mm, and a portion of the roll was sticky. I was able to unroll some of it to get a good look at the images. I dated the film to roughly 1912-1914. Then it dawned on me…this is probably nitrate.
Unrolling it a bit more revealed the dreaded “NITRATE FILM” on the edge of the film stock. My instant reaction was, “Oh fuck.”
The nitrate was obviously in stage 2 of decay and very quickly moving to stage 3 because it was starting to bubble. I immediately put a plan into action to have a film specialist assess its condition and determine whether we could duplicate it (we did). Then I had to figure out what to do with it because my archive was not able to store nitrate long-term. I ended up depositing it in an authorized facility with a specialized vault.
In the weeks it took to coordinate all of this, that damn nitrate film sat by my desk. I would stare at it. I’d warily open the box to check on it. I would talk to it.
“Don’t you dare catch on fire. Don’t even think about it.”
“You better behave, dammit.”
Storing & Preserving Nitrate
We decided to send that sucker to an authorized facility because we didn’t have the proper environment to safely store it. Archival standards and the National Fire Protection Association (NFPA) require nitrate’s environment to be as cold as possible, but they highly recommend freezing. It must be in a ventilated container to prevent explosions. It’s also best to keep it isolated from other collections and humans because of the gases it emits while it decays. The storage unit or vault should have a built-in sprinkler system and vents. We didn’t have an isolated storage unit, and the archive was in an office building in New York City, so not ideal.
Since the U.S. Department of Transportation deems nitrate a hazardous material, we had to get an authorized carrier to ship it to its final destination. All in all, it was a lot of coordination, but I was happy to get that nitrate away from my desk and out of the archive.
When handled properly and stored in specialized environments, nitrate film doesn’t seem all that scary. And generally, it isn’t. If you don’t give nitrate the conditions it needs to burn, it won’t burn. I survived my nitrate encounter without problems because I followed the proper procedures.
However, there have been several incidents since the 1890s when nitrate film proved disastrous and fatal. To learn about historic nitrate fires and explosions, be on the lookout for my next post, This Film is on Fire: Nitrate Film Disasters.
You can also check out the following books to learn more about nitrate film and film preservation. I earn a commission if you make a purchase, at no additional cost to you.
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Footnotes
- Eastman Kodak Company, “Chronology of Film.” ↩︎
- National Film Preservation Center, The Film Preservation, 16. ↩︎
- Full citation: Photograph No. 64-NAD-147; “Sample of Deteriorated Motion Picture Film Found at the White House Garage,” January 17, 1936; Photographic Prints of Storage Conditions of U.S. Government Records Before Accession to the National Archives, 1935-1944; Records of the National Archives and Records Administration 1789-ca. 2007, Record Group 64, National Archives at College Park. ↩︎
- Full citation: Photograph No.64-ND-3931; “Deteriorated Nitrate Base Motion Picture Film,” 1969; Historic Photograph File of National Archives Events and Personnel; Records of the National Archives and Records Administration 1789-ca.2007, Record Group 64, National Archives at College Park. ↩︎
- Full citation: Photograph No. 64-NA-1-493; “Deteriorated Motion Picture Film (Nitrate) in Bubbling Foam Showing Deterioration of Acetate Core,” July 11, 1949; Historic Photograph File of National Archives Events and Personnel; Records of the National Archives and Records Administration 1789-ca.2007, Record Group 64, National Archives at College Park. ↩︎
Bibliography & Further Reading
*Several of the following links are Amazon affiliate links, which means I earn a commission if you make a purchase, at no cost to you.
Amidon, Audrey. “Film Preservation 101: Is Nitrate Film Really Dangerous?” The Unwritten Record (National Archives and Records Administration blog), December 10, 2018.
Eastman Kodak Company. “Chronology of Film: History of Film from 1889 to Present.” Kodak. Eastman Kodak Company. Accessed November 7, 2024.
Eastman Kodak Company. “Storage and Handling of Processed Nitrate Film.” Kodak. Eastman Kodak Company. Accessed November 7, 2024.
Heckman, Heather. “Burn After Viewing, or, Fire in the Vaults: Nitrate Decomposition and Combustibility.” American Archivist 73, no. 2 (2010): 483-506.
Library of Congress. “Care, Handling, and Storage of Motion Picture Film.” Library of Congress. Accessed November 7, 2024.
National Film Preservation Center. The Film Preservation Guide: The Basics for Archives, Libraries, and Museums. San Francisco: National Film Preservation Foundation, 2004.
Ritzenthaler, Mary Lynn, and Diane Vogt-O’Connor. Photographs: Archival Care and Management. Chicago: Society of American Archivists, 2006.
Smither, Roger, and Catherine A. Surowiec, eds. This Film is Dangerous: A Celebration of Nitrate Film. FIAF, 2002.
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