Cores

Film cores make a convenient centre for the film that enables the film to be placed on winding equipment, and other film transport mechanisms, without damage to the film at the centre of the reel.

Fig 8.1 Film cores

Film cores are specific to the format i.e. 35mm wide cores for 35mm film. Smaller gauges of film, e.g. 16mm or 8mm, may be stored on projection reels.

It is not good practice to use adhesive tape to secure the film to the core for any reason. Not only are there concerns over the suitability of the adhesive but the sudden shock when the film is unwound and reaches the end can cause cinching.

Core diameter

The film core size plays a significant role in some forms of curl that develop during long term storage. A larger diameter core, either 75 or 100mm, will help reduce the effect of 'cold flow curling’. The smaller 50mm cores can be used although they are not recommended for this reason.

Cold flow curling occurs when the film base polymer adjusts to a new shape over a long period of time. In the instance of film the base will take on the curve of the film reel, the smaller the diameter the tighter the curl effect. Cellulose triacetate is faster to react to cold flow curl than polyester, however cellulose triacetate is also faster to reverse the curl. The cold flow curl in polyester film is referred to as core set. Core set can be reversed over time, however it does create handling issues.

If a film has developed cold flow curl then rewind the film in the opposite direction around the core, i.e. if the film was originally wound emulsion in, then rewind the film emulsion out.

Core materials

The materials that the core is made from is very important. Whatever is used must not harm the film in the short or longer term.

In general a 'safe’ plastic is most suitable. Cardboard and wood should not be used.

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