INTRODUCTION
New technologies are adopted based on their advantages, and disadvantages are considered later or sometimes not at all. Preservation often involves working to mitigate those disadvantages and, in the case of photography, this means working to increase the stability of inherently unstable materials.
There are three broad types of film-based photographic materials: cellulose nitrate, cellulose acetates, and polyester. These materials have been used as a support for negatives, positive transparencies, motion pictures, microfilm, and other photographic products. Unfortunately, cellulose nitrate and cellulose acetates are unstable. The products of their degradation can severely harm and even destroy photographic collections, in addition to posing serious safety hazards.
IDENTIFICATION
Nitrate Film Base
In August 1889, Eastman Kodak began selling the first photographic negatives on cellulose nitrate flexible film support. This innovation was the foundation of an entirely new era in photography. The increased convenience of flexible films enabled professional photographers to take more photographs under a wider variety of conditions; it also created a new amateur market which quickly became the economic foundation of the photo industry.
Nitrate film remained in production in various formats until the early 1950s.
As a photographic support, nitrate film had some serious disadvantages. The film was, and is, highly flammable, and it releases hazardous gases as it deteriorates. Large quantities of nitrate film have caused several disastrous fires. Due to the inherent instability of cellulose nitrate, much of our photographic legacy from this period is disappearing.
A photographic collection that contains any flexible, transparent film negatives from the time period of 1890-1950 is very likely to contain at least some nitrate film. Since these negatives need special attention, they should immediately be separated from other negatives. Deteriorated nitrate negatives are easy to identify, but nitrate negatives in good condition are almost visually indistinguishable from other types of transparent films. There are four ways to identify nitrate negatives.
1. Edge printing
Nitrate Kodak notch code (at right) and printing
Acetate Kodak notch code (at right) and printing |
Many manufacturers stamped professional sheet films with an identification along one border. The words generally identified the manufacturer and the type of film: nitrate or safety. Unfortunately, not all manufacturers adopted edge printing identification. It wasn’t done on either early nitrate negatives or onsome roll film formats. Amateur roll films were not marked but can be identified by their tendency to curl very tight scrolls
(later roll films were coated on both sides to prevent such curling). Notch codes can also identify sheet film as nitrate. A "V" notch code (first from the edge) will identify pre-1949 Kodak sheet film as nitrate while a “U” shaped notch (first from the edge) will indicate the Kodak film is acetate. Note that a nitrate negative may have been copied at some point and the edge printing from the original will appear on the copy. Therefore, just because you see the word “nitrate” does not guarantee that it is. See the section on testing to be sure.
2. Dating Information
The dates Eastman Kodak stopped the manufacture of nitrate film are listed in the table below. If a negative can be accurately dated, either by subject or by the photographer's notes, it is possible to determine if it is nitrate film.
Eastern Kodak Company Nitrate Film Types | |
| Type of Film (see notes) | Last Year of |
X-ray films | 1933 |
Roll films in 35mm (A) | 1938 |
Portrait and Commercial sheet films (B) | 1939 |
Aerial films | 1942 |
Film Packs (C) | 1949 |
Roll films in sizes 616, 620, etc. (D) | 1950 |
Professional 35mm Motion Picture films (E) | 1951 |
NOTES for Type of Film table
A. It has always been a common practice for photographers to purchase bulk rolls of 35mm motion picture film and re-spool it into cassettes for still camera use. It is possible to find still camera negatives on nitrate film for an additional 13-year period after this date.
B. Nitrate sheet film tends to have a very thick and rigid base. Additionally, professional sheet film negatives will have notches on one corner. These notches are used by photographers to determine the emulsion side in the dark.
C. Film pack negatives were produced in the same sizes as sheet film. Film packs used a much thinner and a very flexible based film. These negatives will feel like roll film. They lack a notch code, but may have a negative number, generally 1 through 12.
D. These sizes were called amateur roll film formats. Many families may have a small number of these negatives stored in their home with no idea of the hazard they represent.
E. Professional 35mm motion picture film is the most hazardous type. All nitrate 35mm motion picture film should be duplicated by an authorized laboratory. Then the nitrate motion picture film should be disposed of by the local fire marshal or a hazardous materials disposal service. NOTE: 16mm, regular 8, and super 8 movie formats were considered amateur formats and were always made on a safety film base.
Unfortunately, Eastman Kodak is the only manufacturer that has supplied any dates on nitrate film production. These dates do not apply to other manufacturers' films, nor do they give an indication of when Kodak started selling safety films. For example, nitrate sheet film production ended in 1939, but Kodak began test marketing safety based sheet film sometime in the mid-1920s. For most formats, there was a carryover period when both types of film were made.
3. Nitrate film base deterioration
 |
Level 1 No deterioration.
Level 3 The film becomes sticky and emits a strong noxious odor (nitric acid).
|
A third method of film base identification is based on the observations of deterioration characteristics. Nitric oxide, nitrous oxide, and nitrous dioxide are all released as gases from the decomposition of cellulose nitrate. In the presence of atmospheric moisture, these gases combine with water to form nitric acid. The formation of nitric acid acts to further degrade cellulose nitrate film, and it can destroy enclosures in which the negatives are stored. It can even damage materials stored in close proximity to the collection.
Because of their extreme flammability, institutions should isolate and properly store cellulose nitrate materials—especially when those materials are in a deteriorated condition. They should be stored in a controlled environment of relatively low humidity, or ideally, in cold storage.
Cellulose nitrate decomposition can be very rapid. Deterioration is generally categorized in six progressive stages:
Most negatives will retain legible photographic detail into the third stage of decomposition. These negatives may become brittle, but—with careful handling—they can be duplicated. Negatives in the fourth, fifth, and sixth stages of decomposition generally have decreasing areas of legible image and should be either placed in cold storage or digitized before the image completely fades away.
Monique Fischer
Senior Photograph Conservator
Northeast Document Conservation Center
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