By drawing on information about how film has behaved in the past, this gauges and stocks section makes suggestions for what to consider and what signs of decay you should keep an-eye-out for, when approaching different types of film stock.

Gauges
There are essentially four different film gauges in use today; 35mm, 16mm, super 16 and super 8.  Super 16 is16mm wide and super 8 is 8mm, but both these gauges push further into the sprocket area than the standard same width gauges, and in doing so succeed in increasing the size of their frame and thus the definition of their image. 

Kodak also makes reversal stocks of all the current gauges, meaning you get a positive print back from the lab but no negative. See Copies section for more information.

The link below provides a lengthy but comprehensive history of the numerous different gauges used in the past, including 9.5mm, a gauge still maintained by enthusiast groups but no longer being made in the lab.   Originally featuring in the quarterly of the Fotografica Society, Netherlands, it comes with illustrations and photographs of the different stocks and cameras.

www.xs4all.nl/%7Ewichm/filmsize.html

All film gauges are made up from the same structure of a base layer and a covering emulsion that holds the picture.  The base layer for 35mm was originally made of cellulose nitrate, a highly unstable material prone to self-combustion.   The production of nitrate ceased in 1951 and many calls have been made to recover any remaining stocks still hidden away. 

35mm is traditionally associated with feature films while the smaller 16mm and 8mm gauges are commonly attributed to home movie and/or low-budget films.   These smaller gauges initially used a base made of acetate, often referred to as 'safety'.  Whilst not exactly dangerous like nitrate, acetate suffers a different chemical deterioration know as vinegar syndrome. 

Vinegar Syndrome
The name vinegar syndrome derives from the acrid, vinegary smell produced when the acetate base decays.  Acetate is sensitive to heat, moisture, humidity and acid and all these factors encourage changes in the chemical state.  As well as producing the vinegary acetic acid, on deterioration, the base also produces a white powder or plastizer that gather s round the side of the film.  Once this reaches a critical point, deterioration is rapid.  The film becomes brittle and shrunken and past this state the film literally decomposes.

Vinegar syndrome is contagious; if you suspect a film is turning, separate it from your other films.  To save the images on the film, get it transferred. This may be the only chance to rescue the picture, so think carefully whether to transfer it at home or at a lab and to what medium.  If the film has already shrunk, labs can temporarily resize it and have a negative struck and new prints made.

The acrid vinegary smell is a clear indication that a film has vinegar syndrome but an acidity test can detect it before this stage begins and thus give you more time to take action.  You can slow the decay by placing a 'molecular sieve' in the can, in with the film.  This absorbs the gases and retards the decay.

The link below provides some basic instructions for vinegar syndrome testing.  This test uses A-D (acidity detection) strips.  The information in the link notes how these are placed in a can for a day or so and then removed and compared to a calibrated colour chart.  (For information about stockists of A-D strips go to the resources section within film.)

www.filmpreservation.org/preservation/testing.html

Polyester
A new 16mm and 8mm polyester base was introduced in the 1950s.  Stronger and thinner than acetate, the polyester base is impossible to tear and, as film cement will not take to it, must be joined either electronically or with tape.  It also provides greater chemical stability and, most significantly, no risk of vinegar syndrome.  

The fact that it won't tear, however, could be problematic.  Tales are told of large projectors being pulled of their stations as the polyester print inside refuses to be broken.  

Colour and Black and White
Black and white stocks are much more stable than colour.  The silver metal particles in black and white films almost only deteriorate on exposure to high humidity while the dyes in colour films break down far easier.  Colour films are made-up of three layers of dye that through combination yield full colour.  The layer that provides the yellow is the most susceptible to fading and in its absence stocks take on the pinkish quality that is sometimes seen in older colour films.

Unlike the standard colour negative stocks, reversal film is known for its long -term stability and brightness of colour.  It does however come with its own causes for concern; the copies section provides details.

Sound tracks
There are two different types of synchronised film soundtrack, optical and magnetic.  Optical sound tracks are visual renditions of sound wave forms and provide sound through their reception and translation with a light beam in the projector.  Magnetic sound tracks are made up from an encoded magnetic signal and are essentially the same as that which runs through an old tape cassette player.  Like a tape player, these signals are decoded or played by a tape head.

Because of their dependence on light, optical soundtracks loose their definition with multiple film copying, an eventuality possibly necessary in light of a missing negative.

Magnetic sound tracks can be joined with the moving image but sometimes turn-up as a separate perforated magnetic tape that looks similar to film.  If you do use, or have films with a magnetic track, you should keep them away from strong magnetic signals, like televisions.   These can weaken or wipe the magnetic sound signal.   Magnetic sound on an acetate base is also more prone to vinegar syndrome than a film with just the image. 

Unlike the film image that creates the illusion of continuity, sound tracks are continuous.  This means that if you cut and splice film with a combined soundtrack, the image will cut cleanly but the sound track will probably produce a cracking sound.  Fingerprints on the film may also produce cracking or interference.

Should you wish to use sound, there is of course no reason for employing either a magnetic or an optical sound track.  You could use a secondary source to play alongside   your images but bear in mind that precise synching may be difficult.   If you do use a secondary source, make sure you look after and document it precisely, as you would with the film it accompanies.   You might also want to keep yourself informed for the future by looking into the technological information and history of the medium of this other source.

This Canadian archives and libraries link provides straightforward information for looking after CDs, home audiotape and vinyl.

www.collectionscanada.ca/6/28/s28-1019-e.html#a11

If sound is of particular interest, this link goes to another preservation link page, both long and comprehensive.  This comes from the American, Conservation On-Line.

palimpsest.stanford.edu/bytopic/audio/