Fundamentals of AV Preservation - Chapter 1

Section 4: Film

4.1 History

	FIGURE  1.17 Film gauge comparison chart. Credit: Ryan Edge (CC BY-SA)

Film has a long history dating from the 1890s, lasting through to today. Due to technological limits, films began in the 1890s at less than a minute long and remained silent until 1927. The first commercially exhibited film in the United States was 35mm, which remains the industry standard today. Smaller gauges, such as 16mm and 8mm, are less expensive to use and are more popular in the amateur market. 16mm was introduced in 1923 by Kodak and is the most common gauge present in today’s libraries and archives.8mm was introduced by Kodak in 1932 and marketed to amateur film enthusiasts. Other gauges, such as 28mm and 9.5mm, are much rarer but may be present in your collections.

Film can be broken down into three main types consisting of image, optical sound, and magnetic sound. Each of these types has multiple sub-types and variants. While it is true for all media types, film more than any other demands an understanding of production and post-production processes and workflows in order to properly interpret what a given piece of film media is and how it should be considered, prioritized, and treated. A deep dive into the particulars of film production and post-production workflows and the corresponding media outputs is beyond the scope of this chapter, although the reader is strongly advised to review the additional resources that cover these topics.

4.2 Materials and Preservation Risks 

The three most common bases for film consist of nitrate, acetate, and polyester. Contrary to audiotape, polyester film is translucent when held up to the light and acetate is opaque. 

The earliest of the three film bases in production was nitrate; notorious for its combustible properties, it became well known for the cause of major fires in projection booths, storage spaces, and archives. When nitrate is subjected to high heat and humidity, it can combust. Nitrate may be identified through edge printing or edge code if the manufacturer took advantage of this convention. Readers should note that it is also possible for the edge printing on nitrate film to be transferred to other film stocks in the film-to-film reformatting process. If nitrate is identified, it should be moved to a cold storage environment and prioritized for preservation reformatting. Decay in nitrate film is identified through discoloration, stickiness, odor, self-adhesion, deformation, and ultimately disintegration.

	FIGURE 1.18 Polyester film (left) vs. acetate film (right). Credit: Preservation Self-Assessment Program University of Illinois at Urbana-Champaign

In 1909, acetate film⁶ followed nitrate film, introduced as “safety film” due to its noncombustible properties. While safer than nitrate, acetate eventually demonstrated its own significant degradation mechanisms, the most common of which is known as “vinegar syndrome” due to the resulting odor. Promoted by storage conditions, the vinegar smell is a result of acetic acid production from a catalytic degradation process that is logarithmic in nature. At a certain point of degradation the speed of decline is greatly increased, progressing from brittleness and a vinegar odor to delamination and decomposition. An early form of acetate known as diacetate can give off an odor of camphor or moth balls as it degrades. This process is known as “napthalene syndrome.”⁷ While not as widely used as acetate, diacetate film may exist in archival collections.

Polyester was the latest film base to be introduced in the 1950s and has not yet exhibited significant degradation mechanisms, though discoloration and fading may occur.

Film image and sound can be together on one film (composite) or separated onto multiple films (separations) depending on what type of recording it is and at what point in production or post-production process it was created.

The aforementioned film deformation resulting from degradation will negatively impact the ability to reproduce film images and magnetic and optical sound alike. Discoloration and fading can be an issue with polyester and acetate film bases, impacting both film images and optical sound tracks.

Depending on the type of film recording and where in the production or post-production workflow the film was created, there may be significant splices. These may consist of either tape splices or cement splices. Poor quality splices or degraded splices can result in the failure to bind two pieces of film together or cause an artifact in the image or sound.

Film is often stored on film cores without a reel or flanges, just like an open reel audio pancake. (See the polyester reel pictured above.) As with pancakes, film on cores is prone to becoming loose and unspooling, resulting in a mess of film that is difficult to put back in order.

Improper storage, care, and handling practices may result in the following film issues, impairing reproduction:

FIGURE 1.19 A film with optical sound. Credit: AVP

• Scratches, resulting in loss of image content and artifacts in image and sound.
  
  
• Fading or discoloration of the image or optical sound.
  
  
• Deformation of the film, causing distortion of the light as it passes through the film or poor contact between magnetic film and the magnetic head.
  
  
• Decomposition and delamination of the emulsion layer, resulting in loss.
  
  
• Matter such as dirt, dust, hair, and even fingerprints that create separation between the magnetic film and the head.
  
  
• Broken or poorly repaired splices.
  
  
• Film that is unwound from cores.
  
  
• Magnetic particles that were originally recorded, but were exposed to a magnetic force that changed their magnetic state.

4.3 Reproduction Methods

The reproduction method for film images, magnetic sound, and optical sound are all different. Like magnetic tape, magnetic film sound uses electromagnetic means of reproduction. Therefore the same concerns exist regarding contact with the head and potential factors that may disrupt good contact.

There are two types of optical film sound, consisting of variable density and variable area. Both utilize an optoelectronic method of reproduction, shining light through the film into a light sensor on other side that converts light values to electrons.

Film images are reproduced through the projection of light through an image; the light that passes through the image may end up on a screen for viewing purposes. When digitizing, the light that passes through the film is read by photoelectric sensors that convert the light to electrons. Whether a film is a positive or a negative will impact the digitization process.

4.4 Best Practices for Storage and Handling

Environment

• Film image and optical sound should be stored at temperatures between -4 and 46 degrees Fahrenheit, with RH between 30%-50%. Temperatures should not fluctuate more than ±3 degrees within a 24 hour period. RH should not fluctuate more than ±5% within a 24 hour period.
  
  
• Film magnetic sound should be stored at temperatures between 32 and 61 degrees Fahrenheit,⁶ with RH between 30%-50%. Temperatures should not fluctuate more than ±3 degrees within a 24 hour period. RH should not fluctuate more than ±5% within a 24 hour period.
  
  
• Film images and optical sound should be kept out of light when not being used.
  
  
• Magnetic film sound should be kept away from magnets, items containing magnets, and items generating magnetic force.

Housing

• 	FIGURE 1.20 Store film on its side, lying horizontally. Credit: AVP

  Film should be stored on its side so that it lays horizontally.
  
  
• The end of a film should be taped down, either to itself or the reel flange, using “hold down” tape intended for this purpose.
  
  
• Film should be in housing that protects it from external elements.

Handling