Film base
A film base is a transparent 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.- Human medicine :Sensitivity of the skin to a light source can take various forms. People with particular skin types are more sensitive to sunburn...

An emulsion is a mixture of two or more liquids that are normally immiscible . Emulsions are part of a more general class of two-phase systems of matter called colloids. Although the terms colloid and emulsion are sometimes used interchangeably, emulsion is used when both the dispersed and the...

 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
Film stock
Film stock is photographic film on which filmmaking of motion pictures are shot and reproduced. The equivalent in television production is video tape.-1889–1899:...

. Historically there have been three major types of film base in use: nitrocellulose
Nitrocellulose is a highly flammable compound formed by nitrating cellulose through exposure to nitric acid or another powerful nitrating agent. When used as a propellant or low-order explosive, it is also known as guncotton...

 (cellulose nitrate), cellulose acetate
Cellulose acetate
Cellulose acetate , first prepared in 1865, is the acetate ester of cellulose. Cellulose acetate is used as a film base in photography, as a component in some adhesives, and as a frame material for eyeglasses; it is also used as a synthetic fiber and in the manufacture of cigarette filters and...

, (cellulose triacetate
Cellulose triacetate
Cellulose triacetate, also known simply as triacetate, CTA and TAC, is manufactured from cellulose and a source of acetate esters, typically acetic anhydride...

, cellulose diacetate, cellulose acetate propionate, and cellulose acetate butyrate), and polyester
Polyester is a category of polymers which contain the ester functional group in their main chain. Although there are many polyesters, the term "polyester" as a specific material most commonly refers to polyethylene terephthalate...

 (polyethylene terephthalate
Polyethylene terephthalate
Polyethylene terephthalate , commonly abbreviated PET, PETE, or the obsolete PETP or PET-P, is a thermoplastic polymer resin of the polyester family and is used in synthetic fibers; beverage, food and other liquid containers; thermoforming applications; and engineering resins often in combination...

 (PET) (Kodak trade-name: ESTAR)).


Nitrate film base was the first transparent flexible plasticized base commercially available, thanks to celluloid
Celluloid is the name of a class of compounds created from nitrocellulose and camphor, plus dyes and other agents. Generally regarded to be the first thermoplastic, it was first created as Parkesine in 1862 and as Xylonite in 1869, before being registered as Celluloid in 1870. Celluloid is...

 developments by John Carbutt, Hannibal Goodwin
Hannibal Goodwin
Hannibal Goodwin , was an Episcopal priest at the House of Prayer in Newark, New Jersey, 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 animation.-Biography:He was born in...

, and Eastman Kodak
Eastman Kodak
Eastman Kodak Company is a multinational imaging and photographic equipment, materials and services company headquarted in Rochester, New York, United States. It was founded by George Eastman in 1892....

 in the 1880s. Eastman was the first to manufacture this for public sale, in 1889. Unfortunately, nitrate also had the drawback that it was extremely flammable (being essentially the same chemically as guncotton) and decomposed after several decades into a no less flammable gas, leaving the film sticky and goo-like (and ultimately dust).

As this happened, the likelihood of auto-ignition
Autoignition temperature
The autoignition temperature or kindling point of a substance is the lowest temperature at which it will spontaneously ignite in a normal atmosphere without an external source of ignition, such as a flame or spark. This temperature is required to supply the activation energy needed for combustion...

 increased even 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 gate, and several incidents of this type resulted in audience deaths by flames, smoke, or the resulting stampede. While an accident of this kind was recreated in Cinema Paradiso (1988), the risk was certainly far from fictional; in one instance, at the Laurier Palace Cinema in Montreal
Montreal is a city in Canada. It is the largest city in the province of Quebec, the second-largest city in Canada and the seventh largest in North America...

 on January 9, 1927, a fire broke out during a children's film program and resulted in the deaths of 77 children between the ages of 4 and 18.

The year 1978 was particularly devastating for film archives when both the United States National Archives and Records Administration
National Archives and Records Administration
The National Archives and Records Administration is an independent agency of the United States government charged with preserving and documenting government and historical records and with increasing public access to those documents, which comprise the National Archives...

 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 can be very difficult 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 underwater. 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.

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 give off 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 film gate should a trigger piece of fabric ignite. Nitrate film is classified as "dangerous goods", which requires licenses for storage and transportation.


Despite the dangers of the nitrate film base being known practically since its development, it was used in virtually all major motion pictures 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
8 mm film
8 mm film is a motion picture film format in which the filmstrip is eight millimeters wide. It exists in two main versions: the original standard 8mm film, also known as regular 8 mm or Double 8 mm, and Super 8...

 and 16 mm 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
Original camera negative
The original camera negative is the film in a motion picture camera which captures the original image. This is the film from which all other copies will be made. It is known as raw stock prior to exposure....

 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
Film splicer
A film splicer is a device which can be used to physically join together lengths of photographic film. It is mostly used in motion pictures...

 with film cement, while polyester can only be spliced with tape or an ultrasonic splicer, so polyester would be hard to edit
Film editing
Film editing is part of the creative post-production process of filmmaking. It involves the selection and combining of shots into sequences, and ultimately creating a finished motion picture. It is an art of storytelling...

. 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
Persona (film)
Persona is a film by Swedish director Ingmar Bergman, released in 1966, and starring Bibi Andersson and Liv Ullmann. Bergman held this film to be one of his most important; in his book Images, he writes: "Today I feel that in Persona—and later in Cries and Whispers—I had gone as far as I could go...

(1966) or Velvet Goldmine
Velvet Goldmine
Velvet Goldmine is a 1998 British/American drama film directed and co-written by Todd Haynes. The film tells the story of a pop star based mainly on David Bowie's 'Ziggy Stardust' character and is set in Britain during the days of glam rock in the early 1970s.Sandy Powell received another Academy...

, or, if one is unlucky, in real life 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
In organic chemistry, acetyl is a functional group, the acyl with chemical formula COCH3. It is sometimes represented by the symbol Ac . The acetyl group contains a methyl group single-bonded to a carbonyl...

 groups which are attached to long chains of cellulose which form the film base are broken from their molecular bonds and free acetic acid is released with a characteristic smell of vinegar. This is known as vinegar syndrome. As the degradation progresses the film base becomes brittle and shrinks.


Polyester is the most recent film base to have been developed, and 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.

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 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.
  • 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 diphenylalanine 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 consumes the film almost completely. (ONLY PERFORM WITH THE HIGHEST OF CAUTION)
  • 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 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.
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