2. FILM SPECIFICS: STOCKS AND SOUNDTRACKS

2.1   FILM BASES
2.11 Nitrate
2.12 Acetate
2.13 Polyester
2.2   B&W VS COLOR
2.3   REVERSAL VS NEGATIVE
2.4   SOUNDTRACKS
2.41 Super/8mm
2.42 Soundtrack-Picture Displacement
2.43 Magnetic

Motion picture film comes in countless varieties, each with its own idiosyncrasies, but all have the same essential physical structure consisting of two primary parts--the base and the emulsion. The emulsion is the image layer containing the image material (i.e., metallic silver or color dyes) within the gelatin binder. The mass of the film is the base, which is the transparent support on which the emulsion lies. There are three types of bases: acetate, nitrate and polyester.

EMULSION
The emulsion is the thin layer of gelatin in which the photographic image resides. The emulsion side of the film can usually be identified by its dull, tacky finish. The base side appears smooth and shiny. On color film where both sides appear glossy, you may identify the emulsion side by holding the film to a light. The side on which the image appears raised is the emulsion side.

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2.1 FILM BASES
2.11 Nitrate
The earliest 35mm professional film stocks were produced on a cellulose nitrate base. Nitrate film is highly combustible and cannot be extinguished once it has ignited; it has to be allowed to burn itself out. Nitrate film is considered a hazardous material, and as such there are strict laws for projecting, storing and shipping nitrate film. If nitrate film is found in your collection it should be kept as cool as possible, be stored in a vented (not sealed) can, and separated from acetate reels. A film archive should be contacted for further advice. Nitrate has a distinctive sweet odor, but the easiest way to identify it is to first unwind it to the picture area, and examine the edges of the film. After the introduction of safety film in the 1920s, Kodak printed the words 'Nitrate Film' along the edges of many of its stocks. If you're still unsure, there are laboratory tests that can be performed to determine if a film is nitrate or not. Despite its renowned chemical instability, recent studies indicated that nitrate base films can be preserved for extended period of time when kept in proper storage conditions. Ultimately nitrate film should be kept under cold storage temperatures.

For further information about nitrate film, see Kodak's publication Safe Handling, Storage, and Destruction of Nitrate - Based Motion Picture Films (Publication H-182), which is available online. This site gives information on shipping, storage, decomposition, and identification of nitrate film.

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2.12 Acetate
Most 16mm and virtually all 8mm film used by amateur and independent filmmakers isacetate (or more properly cellulose acetate propionate or cellulose triacetate). Acetate is commonly called 'safety' film (as is polyester) because it does not have the combustible qualities that nitrate film has, and therefore was considered to be safe for use in homes. All 16mm and 8mm film produced in the United States (as well as all 35mm film produced in the U.S. after 1951) is safety film.

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2.13 Polyester
Polyester film, also known as Mylar or Estar, was first introduced in the 1950s and in recent years has been increasingly popular for 16mm film negatives and prints. Kodak did not use polyester for its camera films, but they produced Super 8 projection cartridge reduction prints for the commercial market. Fuji used polyester film for its Single 8 system, which was a competitor of Kodak’s Super 8. It was reversal camera stock.

Polyester is thinner than acetate film but much stronger and cannot be torn. It has greater chemical stability and is not subject to vinegar syndrome, giving it a typical lifespan at least ten times as long as acetate film. One of the main drawbacks of using polyester film is that it cannot be spliced with cement, so tape splices must be used (professionals use ultra-sonic splicers). Polyester film can often be identified by the Kodak brand name ESTAR found printed on the edge of the film.

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2.2 BLACK & WHITE vs. COLOR
There are crucial chemical differences between black & white and color film. In black-and-white films the image is made of silver metal particles. The silver image is very stable compared to other film components such as color dyes, and not likely to fade unless it is exposed to high humidity, contaminants or was improperly processed.

The vast majority of color films employ chromogenic dyes produced during processing. Color film consists of three layers of dyes, which render the yellow, cyan, and magenta portions of the color spectrum. Of the three, the least stable in the dark is the yellow layer, which is why faded color films frequently have a pinkish hue to them. Once color has faded, there is no way to retrieve it, aside from some (currently) expensive digital reconstruction processes.

During the silent era, commercially produced films were often tinted and toned. Silent 35mm nitrate films come in a variety of colors; often many different tints and tones were used within one film. Common to small collections are Kodascope brand reduction prints from the 1920s and 1930s, which were 16mm silent and tinted amber or yellow.


Kodak's reversal color process Kodachrome film was introduced in 1935 and quickly became the standard for 16mm and 8mm color movies. The earliest types of Kodachrome were prone to fade, but Kodak perfected the process in around 1938 and these films remain remarkably vibrant, even after several decades. Kodachrome remains a standard for amateur color film.

The professional process Technicolor processes also defied fade. In Hollywood, Technicolor was replaced in the 1950s, by Kodak’s Eastmancolor, which was cheaper and, incidentally, much more prone to color loss. Technicolor prints were still being made through the 1970s for some productions.
Other brands of film have their own idiosyncratic characteristics, for better or worse. Despite the fact that the stability of color dyes has been improved significantly in the mid 1980s color fading remains a major threat for preserving film. This can only be addressed by providing proper storage. [See section 8.]

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2.3 REVERSAL vs. NEGATIVE
The vast majority of 16mm and virtually all 8mm and Super-8 film found in both amateur and independent collections is reversal film. This means that the same piece of film that ran through the camera is developed into a positive image, intended for projection. Because there is no negative, reversal films are unique objects and should be treated with care.

The main advantage to reversal film is that it uses half as much film as the negative/positive process, and therefore is less expensive. The main disadvantage is that each time the film is run through the projector (and in some cases this might be hundreds of times), it is subject to all sorts of stresses and dangers. When duplicate copies of reversal films are made they're usually contact printed onto reversal stock. These copies are almost invariably less sharp and have higher contrast than the originals.

 

When there is a 16mm negative available it is important to remember that it may have gone through the same deterioration (such as color fade) as a print made at the same time. However, it has most likely not faced the same physical risks that a projection print has.

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2.4 SOUNDTRACKS
Older and independently produced films have two types of soundtracks: optical and magnetic. (Hollywood now uses digital tracks in addition to optical ones.) Optical tracks are read by projecting a narrow beam of light through the film, causing a sensor to translate the varying intensity of the light into electrical signals that are further converted to sound. Magnetic (mag) tracks are recorded onto oxide stripes on the edge of the film, which are read by playback heads in the projector. Mag tracks work the same way as audiotape and look similar to tape, appearing as a dull, brownish coating on side of the film.

     

16mm sound prints are much more common than sound Super 8, especially among independent films. Typically, soundtracks were recorded on separate audiotapes (such as reel-to-reel, cassettes, and later DATs). Following mixing, the finished audio track would be transferred to film either as an optical track (if done in a lab), a full-coat mag track, or a composite sound print (picture and track).

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2.41 Super 8 & 8mm
Both optical and mag tracks can be found on super 8 and 16mm, while regular 8 only rarely can be found with magnetic stripes which were added after processing. In fact, it was very rare for early home movies to have soundtracks, as only the most serious amateurs made the necessary expenditures to record sound (though equipment was available as early as the 1930s). In 1973, Kodak introduced a Super 8 sound-on-film system, and cameras began to come equipped with microphones. Additionally, Super 8 film could also have sound stripes added after processing and have soundtracks recorded later (usually in the projector). Some projectors can use it for recording an additional sound track.

To avoid having one side of the film thicker than the other, films with magnetic soundtracks often have a "balance stripe." This is a thin blank mag stripe on the opposite edge of the film from the magnetic sound track that keeps the film level on the reel. Super 8 magnetic sound cameras ran at both 18fps and 24fps, and occasionally the cameras ran at a slightly different speed (usually one frame above or below) than advertised. Obviously, this produces playback problems.

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2.42 Soundtrack-Picture Displacement
Because the projectors' soundtrack heads come after the lens for the picture, the soundtracks are not alongside their corresponding images, but instead precede them. This displacement is 56 frames in regular 8 magnetic (rare), 18 frames in Super 8 magnetic, 22 frames in super 8 optical, 26 frames in 16mm optical, and 28 frames for 16mm magnetic.

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2.43 Magnetic Sound
Films with magnetic tracks (and especially separate full-coat mag tracks) have shown to be more susceptible to vinegar syndrome, and should be monitored more closely than silent films or reels with optical tracks. When possible, tracks should be re-recorded as soon as there is any sign of deterioration. It is possible, especially if the film gets damp, that the track will become sticky and partly adhere to the wrong side of base side of the next layer of film. If this happens when the film is stored heads-out, you will hear a muffled version of the track before you're supposed to, and then again in synch with the picture. If the film is stored tails-out, the muffled sound will be heard as a less-distracting echo.

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