Tearing and scratching of the film base and emulsion layer are the most common forms of physical damage.
Cellulose based films can be easily torn by poor handling. Common places for tearing damage to occur are outwards from perforations and around splices.
Polyester based films are very resistant to tearing. Even so, polyester can tear if the edge of the film is damaged in some other way — for example, cut on a sharp sprocket or broken piece of equipment.
Perforations are particularly prone to wear and damage as this is where the most tension is applied to film while it is being transported through sprocket driven equipment. Small tears leading out from the edges of the perforation are known as 'crowsfooting’ and may eventually tear further. Damage by crowsfooting will cause a film to be unstable during transport through equipment.
Tearing around splices is also common. After many years the cement splices may suffer from loss of plasticiser, causing the area surrounding the splice to become more brittle or the adhesion between the film sections to weaken. This is often described as a 'dry splice’. The brittleness may not be consistent across the whole of the films width. If the splice begins to break apart, part of the splice may hold sufficiently well so that the film will tear rather than the rest of the splice breaking.
Scratching is the most common form of damage that occurs to film materials. All film handling operations involve a degree of risk of scratching. Light scratching is often called rain as it can appear as if rain is falling in the projected image.
Cinching is caused by the action of film moving against itself in the roll. This movement can be caused by loosely wound film, where it has been rewound without sufficient care. As the reel tightens up on itself, any dirt or other irregularities will cause scratching. The result can be seen as fine scratches angled in the direction of the movement (Fig 6.3).
Machine transport mechanisms are another source of scratching. Any dirt that comes in contact with moving film will almost certainly cause a scratch. Machine scratches are usually very long straight lines. It is sometimes observed as a waving line oscillating with a regular frequency (Fig 6.4).
Any scratching on the base of the film will have an effect on the quality of the image by causing the transmitted light to diffract (Fig 6.5). This causes annoying lines to appear on the screen during projection and will be transferred during duplication to either film or video (Fig 6.5).
The emulsion holds the image and as such any scratch will cause a loss of information. Black and white films will show a scratch as loss in density, as well as diffraction on projection. Because colour films are comprised of layers of dyes, a scratch will show as a different colour depending on how far through the dye layers the scratch extends. Any scratch on the base or emulsion will attract dirt that will show very distinctly on projection.
Water damage and other blemishes
Water droplets can cause localised damage to the film emulsion. It is possible that the damaged could be caused either by biological action (e.g. bacteria) or by dissolving the gelatin. Also the emulsion may so strongly adhere to the adjacent layer of film that it can be torn away by careless winding.
Small foreign objects, such as particles of rust, can cause the image or base to become stained. Often 'normal’ cleaning will not remove these marks. The foreign material may have altered the image forming material by chemical action or become permanently attached to the base polymer.