The Power of the Negative
March 2004
Movies have become an important part of the modern culture. Motion pictures are forms of entertainment as well as time capsules of trends, morals and events. They show how people dressed, thought, and found important during the time the movie was filmed. Negatives are the first step in making the movies that everyone sees when they go into the theater. There are several layers on a negative. The top layer is a gelatin layer, which protects the image. The image layer, called emulsion, follows this layer. The emulsion layer is set on tope of an adhesive layer which binds the image to a base followed by a final stabilizing layer of gelatin. Color negatives have more layers. Their base identifies the negatives (Library of Preservation and Conservation). There are three main types of negative bases: Cellulose Nitrate (nitrocellulose), Cellulose Acetate (acetyl-cellulose) and Polyester (polyethylene terephalate) based film.
The first version of the negatives was the highly flammable Nitrate. It was used to preserve the films of the “Golden Age” and was thought to last for a long time when it was originally used. However, care of the film was problematic. It had to be kept in a cool low humidity room to prevent ignition. Once it had been ignited it could not be extinguished. Often if would start to burn while people were watching it in the theaters, ruining the rest of the movie. The Nitrate base was also very prone to deterioration. It would often cause an amber discoloration of the images or become brittle and release a noxious odor. Many films from early Hollywood were lost due to Nitrate base negatives deteriorating too quickly for copying. Acetate was thought to be the answer to the problems that Nitrate brought, and it was used along with Nitrate for many years.
Acetate film is not as flammable as Nitrate, but is also relative to conditions in which it is stored. Despite not being as flammable it is still very sensitive to heat and contains an acetic acid, which is what gives off the vinegar smell when it looses quality (Library of Congress). Acetate was updated in the late 1930s to Diacetate and then to Triacetate in the 1940s. However, the updates were not more effective in preventing deterioration. Only Triacetate is still used. One can figure out if the negative was a type of Acetate or Polyester by seeing how much light the negative permits as well as how the negative tears. Acetate will tear and does not allow as much light through as Polyester which is mostly translucent (Selle).
Polyester based film is more stable then the other two film bases, although it is not widely used in cinema film. It also does not shrink as fast as the other versions. However, it brings concern that the base will separate from the emulsion layers of the film because the emulsion layers do shrink. It is the most used film in other media due to its stability compared to other negative materials. It is used for X-ray and aerial photography as well as graphic reproduction.
Film negatives show what time was like when they were made and range from the highly flammable Nitrate-based film to the rarely use Polyester based. They can show what history gave people as well as what is needed to persevere the film of classic movies by identifying the base of the negative. Film negatives are historical and technical time capsules that everyone enjoys watching.
Sources:
Note: When I went back to my copy of this essay, I found that while I had sourced in the essay itself, I had neglected to include a works cited to show where the sources were. I’ve attempted to find sources that are close to the ones that are listed in the essay and perhaps even the original source. However, as it was four years ago, the original source may have been removed or the site reformatted and information dispersed.
Library of Preservation and Conservation:
I couldn’t find this site, but I found something on the Library of Congress Preservation site which may be the same thing, just renamed.
http://www.loc.gov/preserv/care/film.html
Selle:
I can not find this source since I only have a last name. I assume it was an article I found online but I can’t seem to find it.
Extra Sources:
Why Acetate and not Polyester: A forum discussion on the lack of use of polyester film in media
Sokorra Lewis 