Editing Nitrocellulose (section)

===Nitrocellulose decomposition and new "safety" stocks===
Nitrocellulose was found to gradually decompose, releasing nitric acid and further catalyzing the decomposition (eventually into a flammable powder). Decades later, storage at low temperatures was discovered as a means of delaying these reactions indefinitely. Many films produced during the early 20th century were lost through this accelerating, self-catalyzed disintegration or through studio warehouse fires, and many others were deliberately destroyed specifically to avoid the fire risk. Salvaging old films is a major problem for film archivists (see [[film preservation]]).

Nitrocellulose film base manufactured by Kodak can be identified by the presence of the word "nitrate" in dark letters along one edge; the word only in clear letters on a dark background indicates derivation from a nitrate base original negative or projection print, but the film in hand itself may be a later print or copy negative, made on safety film. [[Cellulose acetate film|Acetate film]] manufactured during the era when nitrate films were still in use was marked "Safety" or "Safety Film" along one edge in dark letters. [[8 mm film|8]], [[9.5 mm film|9.5]], and [[16 mm film|16&nbsp;mm film]] stocks, intended for amateur and other nontheatrical use, were never manufactured with a nitrate base in the west, but rumors exist of 16&nbsp;mm nitrate film having been produced in the former Soviet Union and China.<ref>{{cite book |last=Cleveland |first=David |contribution=Don't Try This at Home: Some Thoughts on Nitrate Film, With Particular Reference to Home Movie Systems |editor1-last=Smither |editor1-first=Roger |editor2-last=Surowiec |editor2-first=Catherine |title=This Film is Dangerous: A Celebration of Nitrate Film |location=Brussels |publisher=FIAF |date=2002 |page=196 |isbn=978-2-9600296-0-4}}</ref>

Nitrate dominated the market for professional-use 35&nbsp;mm motion picture film from the industry's origins to the early 1950s. While cellulose acetate-based safety film, notably cellulose diacetate and cellulose acetate propionate, was produced in the gauge for small-scale use in niche applications (such as printing advertisements and other short films to enable them to be sent through the mails without the need for fire safety precautions), the early generations of safety film base had two major disadvantages relative to nitrate: it was much more expensive to manufacture, and considerably less durable in repeated projection. The cost of the safety precautions associated with the use of nitrate was significantly lower than the cost of using any of the safety bases available before 1948. These drawbacks were eventually overcome with the launch of [[cellulose triacetate]] base film by Eastman Kodak in 1948.<ref>{{cite journal |last=Fordyce |first=Charles |display-authors=etal |title=Improved Safety Motion Picture Film Support |journal=Journal of the Society of Motion Picture Engineers |volume=51 |issue=4 |pages=331–350 |date=October 1948 |doi=10.5594/j11731}}</ref> Cellulose triacetate superseded nitrate as the film industry's mainstay base very quickly. While Kodak had discontinued some nitrate film stocks earlier, it stopped producing various nitrate roll films in 1950 and ceased production of nitrate 35&nbsp;mm motion picture film in 1951.<ref>{{cite book |last=Shanebrook |first=Robert L. |title=Making Kodak Film |publisher=Robert L. Shanebrook |location=Rochester, NY |edition=Expanded second |date=2016 |page=82 |isbn=978-0-615-41825-4}}</ref>

The crucial advantage cellulose triacetate had over nitrate was that it was no more of a fire risk than paper (the stock is often referred to as "non-flam": this is true—but it is combustible, just not in as volatile or as dangerous a way as nitrate), while it almost matched the cost and durability of nitrate. It remained in almost exclusive use in all film gauges until the 1980s, when [[polyester]]/[[Polyethylene terephthalate|PET]] film began to supersede it for intermediate and release printing.<ref name="Van Schil">{{cite journal |last=Van Schil |first=George J. |title=The Use of Polyester Film Base in the Motion Picture Industry — a Market Survey |journal=SMPTE Journal |volume=89 |issue=2 |pages=106–110 |date=February 1980 |doi=10.5594/j00526|doi-access=free }}</ref>

Polyester is much more resistant to [[polymer degradation]] than either nitrate or triacetate. Although triacetate does not decompose in as dangerous a way as nitrate does, it is still subject to a process known as deacetylation, often nicknamed "vinegar syndrome" (due to the [[acetic acid]] smell of decomposing film) by archivists, which causes the film to shrink, deform, become brittle and eventually unusable.<ref name="Distillations">{{cite journal |last=Greco |first=JoAnn |title=Saving Old Movies |url=https://www.sciencehistory.org/distillations/saving-old-movies |journal=Distillations |publisher=[[Science History Institute]] |volume=4 |issue=3 |pages=36–39 |date=November 12, 2018 |access-date=April 23, 2020}}</ref> PET, like cellulose mononitrate, is less prone to stretching than other available plastics.<ref name="Van Schil"/> By the late 1990s, polyester had almost entirely superseded triacetate for the production of intermediate elements and release prints.

Triacetate remains in use for most camera negative stocks because it can be "invisibly" spliced using solvents during negative assembly, while polyester film is usually spliced using adhesive tape patches, which leave visible marks in the frame area. However, [[ultrasonic]] splicing in the [[frame line]] area can be invisible. Also, polyester film is so strong, it will not break under tension and may cause serious damage to expensive camera or projector mechanisms in the event of a film jam, whereas triacetate film breaks easily, reducing the risk of damage. Many were opposed to the use of polyester for release prints for this reason, and because ultrasonic splicers are very expensive, beyond the budgets of many smaller theaters. In practice, though, this has not proved to be as much of a problem as was feared. Rather, with the increased use of automated long-play systems in cinemas, the greater strength of polyester has been a significant advantage in lessening the risk of a film performance being interrupted by a film break.{{citation needed|date=September 2012}}

Despite its self-oxidizing hazards, nitrate is still regarded highly as the stock is more transparent than replacement stocks, and older films used denser silver in the emulsion. The combination results in a notably more luminous image with a high contrast ratio.<ref>{{cite web|last1=Case|first1=Jared|title=Art Talk: The Nitrate Picture Show|website=[[YouTube]]|url=https://www.youtube.com/watch?v=1cH84Owofkk&t=17m40s| archive-url=https://web.archive.org/web/20150506124313/https://www.youtube.com/watch?v=1cH84Owofkk&t=17m40s| archive-date=2015-05-06 | url-status=dead|access-date=10 March 2015}}</ref>