A film base is a
transparent
Transparency, transparence or transparent most often refer to:
* Transparency (optics), the physical property of allowing the transmission of light through a material
They may also refer to:
Literal uses
* Transparency (photography), a still, ...
substrate which acts as a support medium for the
photosensitive Photosensitivity is the amount to which an object reacts upon receiving photons, especially visible light. In medicine, the term is principally used for abnormal reactions of the skin, and two types are distinguished, photoallergy and phototoxicit ...
emulsion
An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Altho ...
that lies atop it. Despite the numerous layers and coatings associated with the emulsion layer, the base generally accounts for the vast majority of the thickness of any given
film stock. Since the late 19th century, there have been three major types of film base in use:
nitrate (until about 1951),
acetate, and
polyester.
Nitrate
In the literature of photography "nitrate" is used as a synonym for the chemical
nitrocellulose
Nitrocellulose (also known as cellulose nitrate, flash paper, flash cotton, guncotton, pyroxylin and flash string, depending on form) is a highly flammable compound formed by nitrating cellulose through exposure to a mixture of nitric acid and ...
. It is also referred to as "cellulose nitrate". Nitrocellulose is
guncotton
Nitrocellulose (also known as cellulose nitrate, flash paper, flash cotton, guncotton, pyroxylin and flash string, depending on form) is a highly flammable compound formed by nitrating cellulose through exposure to a mixture of nitric acid and ...
, the first replacement
propellant for
gun powder in firearms.
![Decomposing Nitrate Film](https://upload.wikimedia.org/wikipedia/commons/e/e4/Decomposing_Nitrate_Film.jpg)
Film stock with a nitrate base was the first transparent flexible plasticized base commercially available, thanks to
celluloid
Celluloids are a class of materials produced by mixing nitrocellulose and camphor, often with added dyes and other agents. Once much more common for its use as photographic film before the advent of safer methods, celluloid's common contemporary ...
developments by
John Carbutt
John Carbutt (1832–1905) was a photographic pioneer, stereo card publisher, and photographic entrepreneur. He came to be the first to use celluloid for photographic film and to market dry-plate glass negatives.
He was born in Sheffield, Engl ...
,
Hannibal Goodwin
Hannibal Williston Goodwin (April 21, 1822 – December 31, 1900), patented a method for making transparent, flexible roll film out of nitrocellulose film base, which was used in Thomas Edison's Kinetoscope, an early machine for viewing mot ...
, and
Eastman Kodak in the 1880s. Eastman was the first to manufacture the film stock for public sale, in 1889. Unfortunately, nitrate also had the serious drawback of being extremely flammable, the characteristic that made it a suitable substitute for gunpowder. It gradually decomposes producing a flammable gas, becomes sticky and, at a late stage of decomposition, the film oozes a gooey fluid, ultimately leading the substance to become dust. As this happened, the possibility of
auto-ignition increased further.
Projection booth fires were not uncommon in the early decades of cinema if a film managed to be exposed to too much heat while passing through the projector's film gate, and several incidents of this type resulted in audience deaths by flame, smoke, or the resulting stampede. An accidental fire caused by the film jamming in the gate formed a significant plot point in the movie ''
Cinema Paradiso'' (1988).
The year 1978 was particularly devastating for film archives when both the United States
National Archives and Records Administration
The National Archives and Records Administration (NARA) is an " independent federal agency of the United States government within the executive branch", charged with the preservation and documentation of government and historical records. It ...
and George Eastman House had their nitrate film vaults auto-ignite. Eastman House lost the original camera negatives for 329 films, while the National Archives lost 12.6 million feet of newsreel footage. Because cellulose nitrate contains oxygen, nitrate fires are impossible to extinguish. The US Navy has produced an instructional movie about the safe handling and usage of nitrate films which includes footage of a full reel of nitrate film burning under water. The base is so flammable that intentionally igniting the film for test purposes is recommended in quantities no greater than one frame without extensive safety precautions. The smoke produced by burning nitrate film is highly toxic, containing several poisonous gases and can become lethal if inhaled enough.
Many nitrate films have been transferred in recent decades to safety stock, and original nitrate prints are generally stored separately to prevent a nitrate fire from destroying other non-nitrate films; the gas they release also affects the emulsion of safety film. Usually nitrate collections are even split up into several different fireproof rooms to minimize damage to an entire collection should a fire occur in one part. It is normal for a theater today to pass rigorous safety standards and precautions before being certified to run nitrate films; this includes a fireproof projection booth, fire chambers surrounding the feed and take-up reels, and several fire extinguishers built into the projector and aimed at the projector's film gate with a trigger released if the film ignites. Nitrate film is classified as "dangerous goods", which requires licenses for storage and transportation.
Nitrate film stock was used in every major film production before about 1951. Many silent films only survived because they were printed to
16 mm film, which did not use a nitrate base. A report published by the United States
Library of Congress
The Library of Congress (LOC) is the research library that officially serves the United States Congress and is the ''de facto'' national library of the United States. It is the oldest federal cultural institution in the country. The library ...
in September 2013 states that 70 percent of all American silent feature films are lost.
Acetate
In the literature of photography "acetate" is used as a synonym for several chemicals:
cellulose acetate
In biochemistry, cellulose acetate refers to any acetate ester of cellulose, usually cellulose diacetate. It was first prepared in 1865. A bioplastic, cellulose acetate is used as a film base in photography, as a component in some coatings, and ...
,
cellulose triacetate,
cellulose diacetate
Cellulose diacetate, sometimes called diacetate, is a synthetic polymer made by treating cellulose with acetic acid. It consists of two acetyl functional groups on each unit of D-anhydroglucopyranose of the cellulose molecule. It was first deve ...
,
cellulose acetate propionate
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall ...
, and
cellulose acetate butyrate Cellulose acetate butyrate (CAB) is a mixed ester thermoplastic derivative of cellulose acetate that contains both acetate and butyrate
The conjugate acids are in :Carboxylic acids.
{{Commons category, Carboxylate ions, Carboxylate anions
Carbon ...
. All have been used separately and in mixtures, to produce film base.
Despite the dangers of the nitrate film base being known practically since its development, it was used in virtually all major
motion pictures
A film also called a movie, motion picture, moving picture, picture, photoplay or (slang) flick is a work of visual art that simulates experiences and otherwise communicates ideas, stories, perceptions, feelings, beauty, or atmosphere ...
prior to 1952, when Kodak completed a four-year conversion program to the sole manufacturing of acetate base film stocks. Kodak began working with acetate "safety film" as early as 1909, and started selling it in 1910 for 22 mm film. Acetate has always been used with
8 mm and
16 mm
16 mm film is a historically popular and economical gauge of film. 16 mm refers to the width of the film (about inch); other common film gauges include 8 and 35 mm. It is generally used for non-theatrical (e.g., industrial, edu ...
formats, as they were originally created for amateur home movie usage, and generally was used for most sub-35 mm formats to minimize risk to the general public. Several formats, such as 17.5 mm, which were often re-slit from 35 mm, were nitrate, however. One of Kodak's reasons for choosing 16 mm instead of 17.5 mm for a standard amateur format width was specifically to prevent nitrate re-slits from being used in home movies.
All motion picture
camera negatives are now shot on acetate film because it is safer than nitrate but not as strong as polyester bases, which may damage the camera rather than the film should a jam occur. Acetate can also be
spliced
Spliced may refer to:
*Spliced, the result of rope splicing
Rope splicing in ropework is the forming of a semi-permanent joint between two ropes or two parts of the same rope by partly untwisting and then interweaving their strands. Splices ca ...
with film cement, while polyester can only be spliced with tape or an ultrasonic splicer, so polyester is hard to
edit
Edit may refer to:
Concepts
* an action that is part of an editing process (including of images, video, and film)
* a particular version that is the result of editing, especially of film (for example, fan edit), or music (for example, radi ...
. Acetate film does not burn under intense heat, but rather melts, causing a bubbling burn-out effect — this can be seen simulated in films such as ''
Persona
A persona (plural personae or personas), depending on the context, is the public image of one's personality, the social role that one adopts, or simply a fictional character. The word derives from Latin, where it originally referred to a theatr ...
'' (1966) or ''
Velvet Goldmine
''Velvet Goldmine'' is a 1998 musical drama film written and directed by Todd Haynes from a story by Haynes and James Lyons. It is set in Britain during the glam rock days of the early 1970s, and tells the story of fictional bisexual pop star ...
'' (1998). It can happen during a film screening when a frame becomes stuck in the projector's film gate. Acetate films are also subject to degradation over time. With exposure to heat, moisture, or acids, the
acetyl groups are broken from their molecular bonds to the cellulose. The now free acetic acid is released into the air. Acetic acid is vinegar, and thus the characteristic smell of vinegar is detected. This is known as
vinegar syndrome
Cellulose acetate film, or safety film, is used in photography as a base material for photographic emulsions. It was introduced in the early 20th century by film manufacturers and intended as a safe film base replacement for unstable and highly ...
. As the degradation progresses the film base becomes brittle and shrinks.
Polyester
In the literature of photography
polyester is
polyethylene terephthalate, which Kodak trade-named "ESTAR".
Polyester is the most recent film base to have been developed. It was first used for specialized photography applications in 1955, but it was only in the 1990s that it became overwhelmingly popular for motion picture prints. It is highly preferable for post-production, exhibition, and archival purposes because of its flexibility, strength, and stability. Its strength is sometimes also seen as a disadvantage, however, in that polyester-base films are so resistant to breakage that they are often more likely to break the film equipment should a jam, or extra tension, occur. Movie cameras therefore do not use this base for shooting the original camera negative, as it is vastly preferable, and less costly in time and money, for the film to break instead of the camera. In addition, cameras require a
lap-spliceable triacetate base to allow the use of all of the negative stock.
PET film base can be ultrasonically spliced or by melting and joining the ends of two films together.
Identifying a film base
There are several factors which can aid in identification of the film base of a roll of film. Many are not 100% conclusive, and it is best to use a selection of these to positively verify a film base.
* Printing along the edge of the film:
** for older films, will often say "nitrate" or "safety" on it, however this text may print through from a negative or other intermediate stock.
** may include a date code
Kodak H-1: Film Identification
retrieved 28 March 2007. (Kodak print films prior to 2001) or an actual printed 4-digit year.
** may include an emulsion number uniquely identifying the print stock (newer stocks, only)
* No Kodak film manufactured after 1951 is nitrate, and no film of any kind is polyester before 1955 (and which was initially introduced by DuPont, not Kodak—Kodak came much later, after DuPont had abandoned the market).
* Deterioration artifacts are distinct between nitrate (noxious nitric acid gas; amber discoloration; soft, sticky, or powdery film) and acetate (acetic acid gas, red or blue discoloration, shrinkage, brittleness, presence of bubbles or crystals).
* Polyester shows red and green interference colors when viewed through cross-polarized filters.
* A solution of diphenylamine and sulfuric acid will turn nitrate deep blue.
* A highly controlled burn of one frame of nitrate will result in a bright yellow flame which almost completely consumes the film. (Note that nitrate film is considered a regulated material in many jurisdictions - intentionally burning it is generally strongly discouraged due to safety concerns, as well as potential legal liability.)
* Nitrate film is soluble in a variety of solvents - namely methyl alcohol, ethyl, and ether.
* Float testing of the specific gravity of the base in trichloroethylene
The chemical compound trichloroethylene is a halocarbon commonly used as an industrial solvent. It is a clear, colourless non-flammable liquid with a chloroform-like sweet smell. It should not be confused with the similar 1,1,1-trichloroethane, w ...
should cause nitrate to sink, acetate to float, and polyester to remain around the middle. However, this can be complicated by impurities and deterioration factors.
* Light aimed through the side of a roll of film will shine through if it is polyester, but will not if it is acetate.
* Polyester film is very strong and hard to tear off, unlike acetate.
References
;Notes
;Further reading
* Wilhelm, Henry and Carol Brower.
The Permanence and Care of Color Photographs: Traditional and Digital Color Prints, Color Negatives, Slides, and Motion Pictures, Chapter 19 - Frost Free Refrigerators for Storing Color and Black-and-White Films and Prints
'. Grinnell, Iowa : Preservation Publishing Company, 1993.
* National Film Preservation Foundation
The Film Preservation Guide - The Basics for Archives, Libraries, and Museums
'. San Francisco, California : National Film Preservation Foundation, 2004.
NEDCC Technical Leaflet - A Short Guide to Film Base Photographic Materials: Identification, Care, and Duplication
External links
{{Photography
Film and video technology