Chapter 3
Flexible Negatives

This chapter discusses paper-based stripping films, and self-supported films of gelatin, nitrate, acetate, and celluloid.

There have been many inventions that were conceptually correct but that suffered from early commercial problems caused by materials limitations. Some prominent examples were the pneumatic automobile tire, cylindrical phonograph records, and flexible photographic negatives.

The first negative of any kind was Talbot's paper calotype. Glass plates coated with sensitized collodion soon superseded calotype negatives and dominated photography for three decades. But glass plates were heavy, breakable, expensive, and had to be loaded in the camera one at a time. The fledgling plastics industry was able to mold Daguerreotype cases but not thin transparent flexible films of optical quality capable of resisting photographic chemicals.

Stripping films:
Attempts were made to coat glass plates with collodion or gelatin, then to strip off the coatings and expose them in cameras without the glass. But the films were flimsy to handle, they swelled erratically in solutions, and their light sensitivity was much too low.

The first Kodak camera, No. 1, used stripping film in a round format 2 1/2 inches in diameter. The silver gelatin emulsion was coated on a sub layer of soluble gelatin on a strip of paper base holding 100 frames. After exposure by the customer the camera was returned to Eastman Kodak for processing. The paper was steamed to dissolve the soluble layer, and the emulsion was transferred to clear gelatin for development and printing.

This process was first introduced in 1886 and used in Kodak No. 1 in 1888; it was available until 1891, although Kodak No.2 with a 3 1/2 inch format was introduced in 1889. It was gradually supplanted by the nitrate base; these processes overlapped chronologically.

In order to make the most of the compactness and light weight of stripping films, one more invention was needed, and it appeared right on cue - the spool. Actually it was a complete mechanism with supply and take-up spools and rollers for holding the film flat. Eastman and Walker patented their roll film holder in 1884. Leon Warnerke had patented a roll-film holder in 1875 for gelatin silver bromide emulsions on paper, and Melhuish and Spencer also patented a roll holder for calotypes in 1854, but neither came into general use. Litigation ensued as it did so often in the evolution of photography, but the Eastman-Spencer holder was the right product at the right time. The first Kodaks used rolls of paper negatives, but the paper grain was objectionable just as it had been in calotypes, and Eastman paper negatives were supplanted by stripping films within a year. Stripping films, in turn, lasted about six years until good quality nitrate film appeared.

Surviving specimens of stripping films are relatively fragile and rare; informed recognition and careful handling are necessary if remaining examples are to be saved.

Cellulose Nitrate:
Collodion film base was patented in 1856 but the fabricated product remained poor in quality for the next thirty years. Celluloid, invented in 1869, is a thermoplastic cellulose nitrate, often called guncotton, plasticized with camphor. This formulation, while adequate for billiard balls and shirt collars, was unsuited for optically clear sheets. For a time John Carbutt in Philadelphia made and sold photographic plates cut from solid blocks of celluloid; this heroic process produced unbreakable plates lighter than glass, but still not a roll film.

Manufacturing technology finally caught up with need in 1889 when Eastman chemists patented the first nitrate film. Like celluloid it was basically cellulose nitrate, but with different plasticizers and solvents. In 1892 Samuel Turner invented the familiar black paper backing with numbers visible in a red window. It was marketed by the Boston Camera Company, which George Eastman soon bought and merged. Photography had come a long way in six decades.

The Need for Safety Films:
Collodion, celluloid, and nitrate films are all extremely flammable. Fires from nitrate film in movie projection booths were not uncommon as the movie industry grew. The displaced vaudeville industry had adopted asbestos stage curtains; movies put the hazard at the other end of the theater. Film was obviously flammable, but safety film had not yet been invented, so fires had to be accepted as an unavoidable risk in a new and exciting entertainment medium.

The long-term problem of inevitable spontaneous decomposition of nitrate film in all storage conditions was slower to be recognized. Nitrate film evolves fumes containing nitric acid and various organic decomposition products, ending in total disintegration or fire. The flash point may go as low as 120 degrees Fahrenheit. The rate of decomposition depends on the original formulation, film thickness, and type of roll. Cine film is more hazardous than flat sheets because it is tightly rolled, and the decomposition products cannot escape as rapidly as they form, thus accelerating decomposition.

Students of chemistry may see an apparent contradiction with the usual rule that reaction products on the right side of a chemical equation must be removed for the reaction to proceed. This is true of simple reactions, but nitrate film is inherently unstable (does not reach equilibrium), and deterioration is caused by complex reactions whose products are progressively corrosive. The most comprehensive and up-to-date discussion of the problem is in the 1985 book by Eastman Kodak [47, 89-93]. A vividly illustrated article by Michael Hager appears in Image [69]. Young [159] also provides a good reference.

Safety film in the form of cellulose acetate first appeared in 1933 in X-ray film, but professional 35mm nitrate film was made as recently as 1951. Dates of consumption of unused stock cannot be ascertained; Eastman Kodak states [47] "any negatives made before 1950 are suspect". The best course of action is to test any negative that does not show the legend "safety film" along the margin.

Several tests are described in reference 47. Safety film will burn, though not as rapidly as the almost explosive combustion of nitrate film. A small clipping of nitrate film sinks in the solvent 1,1,1 trichloroethane (trichloroethylene), while safety film floats. This solvent is obtainable from laboratory suppliers; it is hazardous to breathe. Details of this and other tests can be found in reference 47, and in Rempel [124].

The storage of nitrate negatives is the most serious single hazard in archival management. One long-term solution is to copy the images on modern film and then destroy the nitrate in an approved manner. Freezing is often used as a temporary expedient; its long-term efficacy is debated.

Chronology of Flexible Negatives

The major steps in the evolution of flexible negatives are summarized below. Other individuals published suggestions or otherwise made contributions, and the literature should be consulted for additional details, particularly Gernsheim [61, 405-409] and Eder [48, 485-490].

1855: Frederick Scott Archer patented a collodion stripping film on paper, reinforced with a gutta-percha coating. This appears to be the first flexible transparent negative.

1856-7: variations by Reade, Parkes, and Ferrier, not commercial.

1875: Leon Warnerke produced rolls of chalk-coated stripping paper with collodion or gelatin sensitive layers on a collodion and india rubber substrate. It was made and sold in London for use with his patented roll-film holder.

1882: Alfred Pumphrey manufactured collodion-on-gelatin cut film for plate cameras and the Pumphrey magazine camera.

1883: a commercial stripping film introduced by Georges Balagny in France: sensitive gelatin emulsion on collodion on talc-coated paper for ease of stripping. It was manufactured by the Lumiere brothers who later made the successful Autochrome color film. In 1886 Balagny introduced a sheet film version, comprised of alternate layers of collodion, varnish, and gelatin.

1884: George Eastman patented gelatin silver bromide stripping film on paper; this was manufactured from 1885 to 1889, using the Walker film holder.

1888: John Carbutt of Philadelphia manufactured gelatin dry plates coated on celluloid 0.25 mm thick. They were light and unbreakable, and were made in quantity.

1889: Eastman nitrate film began to supplant stripping film for rolls. Until the early 1900's the film was thin and easily curled.

1892: black paper backing with negative numbers visible through a red window in the camera back, introduced by Samuel Turner of the Boston Camera Co.

Recognition:
Most of the surviving specimens of these types are fragile and yellowed. Their composition can be determined by analytical methods, and possibly by the tests in Rempel [115], but many of the types are sandwiches of different materials such as collodion, gelatin, or rubber. All paper-based negatives and stripping films are of historical interest and can usually be identified by inspection.

Sometimes the image size can be a clue in dating. Following is a list of the standard film sizes, from several sources:

Some image sizes were duplicated on different spool widths: the first number in the listed dimensions corresponds to the roll width. Examples are numbers 103 and 104. Number 103 had the long dimension of the image in the direction of the roll length, while 104 was on a wider spool with the short side of the image in the direction of the roll. When separated negatives are examined, the separation cuts are usually not as straight as the original roll edges, so the image orientation can often be deduced.