Even careful handling may not entirely prevent dirt, dust or oil from accumulating on a film surface.   These can become visible on projection but may also lead to deterioration or decay whether by dirt scratching or acidic finger or projector oils slowly taking their toll.

Set-up
Before you begin cleaning, inspect the film for perforation damage and other tears; these could easily be caught in a cloth and made far worse.  Either clean a damaged film with great care or preferably repair any damage beforehand.  

You can clean off surface dirt by running your film through a soft, folded velvet or cotton batiste cloth held firmly with your fingers.  For a more thorough clean, put some solvent cleaner  (see below) on your cloth and again, run your film through.  You should wind slowly to allow the cleaner to evaporate before the cleaned piece of film moves onto the take-up reel.  Take care to either refold or wash and thoroughly dry your cloth, once it becomes dirty

You can use this method to clean any mould, mildew or fungi from your film's surface too. These can cause severe damage to the emulsion and while they usually form on the wound edge, they can also make their way inside.  The best way to avoid this is to store your film in cool, dry conditions.

You can clean off particular marks of dirt or oil with a cotton bud dipped insolvent.

Various solvents and chemicals have been used to clean film over the years and many are still.   Isopropanol is well considered and can usually be bought from a chemist. Do not use water for cleaning as this can remove the emulsion.

If you want to clean a particularly dirty film, it is recommended that you contact a facilities house.  There are details in the film resources section.  Their procedures may use toxic chemicals and/or specialist equipment.  These include ultrasonic cleaning, buffer roller cleaners and particle transfer rollers.

For more infromation about these and other methods, see www.screensound.gov.au