Nitrate Film - Playing with Fire!
Film expert Frank Wylie describes the ways to detect nitrate film stock, including a "sure-fire" if dangerous method -- ignite it!
Contents
- Origin of Nitrate Film: the Kinetoscope
- Testing for Nitrate Film Stock
by Frank.Wylie@MovieEditor.com
Frank Wylie with a Russian Konvas 35mm camera
Origin of Nitrate Film: the Kinetoscope
Nitrate or nitrocellulose was a base used by manufactures of motion picture film from approximately 1894 to the early 1950s. A derivative of an explosive (gun cotton), this base has withstood the test of time remarkably well. Original examples of some of the very first motion pictures still exist in remarkably good condition. However, the fire hazards associated with this base eventually led to the adoption of "Safety" base stocks on slow-burning acetate.
The Kinetoscope was an arcade device developed by the Edison company. It was a sensation when in 1894 the Kinetoscope Parlor opened in New York City. Thomas Edison didn't patent his invention overseas. Robert Paul of England and others began reproducing and selling copies of the Kinetoscope to arcade owners in Europe and Africa. Edison responded by cutting off all sales of films to the owners of these "unauthorized" Kinetoscopes. Faced with angry customers, European manufacturers were forced into building their own cameras and entering film production to meet the growing public mania for "galloping tintypes".
The Kinetoscope was not a projector. With the Kinetoscope only one person at a time could peer through a small lens. A battery-powered mechanism sped a loop of 35mm film continuously past the viewer's eye and a spinning circular shutter at the rate of about 48 frames-per-second.
Kinetoscopes were capable of holding up to sixty feet of motion picture film -- less than thirty seconds of viewing time. The film width and perforations were much like today's 35mm motion picture film.
By 1896, the Kinetoscope craze began to wane as motion picture projectors were being perfected on a global-scale. Although there were competing film formats such as the Lumiere Cinematograph, the "Edison Standard" for 35mm motion picture stock became the de facto standard through sheer economic force.
Testing for Nitrate Film Stock
Nitrate film stocks can be identified by visible frame line markings, the "float" test, the fluorescent or "backlight" test, and by a simple if dangerous method; the burn test.
With the adoption of safety-base stocks in the mid 1950's, a method was needed to quickly identify Nitrate and Safety stocks at a glance. Nitrate stocks had been imprinted with an inked, visible frame line mark that was oriented across the width of the material. Eastman Kodak simply changed this orientation from across the width of the film to perpendicular to the length of the film stock to denote safety based products. However, not all stocks contain this mark.
Kodak also added a florescent dye in the base of all 35mm (and some 16mm) film stocks. This dye can be detected under a UV lamp as a faint, bluish-purple fluorescence. Nitrate base appears black.
Another test to distinguish between nitrate and safety film was to place a small sample in a test tube of trichloroethylene. If it sinks it's nitrate film. Trichloroethylene was banned. It's about half the toxity of the solvent tetrachloride (that was used for cleaning film).
A conclusive test for a nitrate or a safety film is a burn test, but precautions must be taken. Never ignite film in a roll or even a long piece of film. Nitrate can't be put out, not even by dunking in water! Like a trick birthday candle, nitrate is impossible to extinguish due to the fact that it contains its own oxygen source. However, nitrate film exploding without cause is a myth. If an explosion occurs it's due to built-up gasses that are generated during combustion in a confined area. With this in mind, never burn nitrate in a confined area of any kind and do NOT breathe the fumes from the test burn!.
Only a small sample can be burned safely. Cut off a small sample about the size of one frame of film, approximately 16mm (0.63 in.) wide and 35mm (1.38 in.) long. Bend the film lengthwise and crease it sufficiently so that when released it will stand upright. Stand the film sample (with the crease vertical) on a fireproof flat surface such as an ash tray. Do not do this test in a room containing any film stock!. Go outside or to another location. If a long piece of film is ignited and it turns out to be nitrate a serious burn or a bad fire can result.
With a match flame, ignite one of the top corners of the film. Nitrate film ignites easily, burns downward vigorously with rapidly increasing speed and a bright yellow flame, and is completely consumed in less than 15 seconds. Nitrate film burns with logarithmic speed. If the film sample ignites with difficulty and burns only partially, or if it burns longer than 15 seconds the film can be classified as safety film.
Duplitized nitrate film with emulsion on both sides does not always burn as fiercely as one expects, and sometimes small pieces of safety film held in a match flame burn more rapidly than expected. This field test described in the American Standard Specifications for Safety Photographic Film can't always distinguish nitrate and safety film by burning. If the results are doubtful, laboratory tests should be conducted.
If the results are doubtful, treat the material as nitrate until it can be proven otherwise. Better to be safe than sorry. Nitrate film can be handled safely with careful precautions.
Here are some movies at Film-Tech showing how not to burn nitrate film. Don't do this!
