Identifying Polyester Film Base
If it is necessary to identify polyester film base from other bases then apart from trying to tear the film which cannot be seen as good archival practise, the usual method is rather hit and miss and that is checking to see if when the roll is on edge the film base appears transparent. The most reliable method is to view a piece of film through a pair of crossed polarising filters. Acetate and nitrate film will have no transmission through the filters whilst the polyester will be transparent where there is no image. An even simpler method is to view the film through a single polarising filter by transmission from an LED computer monitor. You must first rotate the filter until it is black and then interpose the polyester film. The picture below shows the effect; nitrate and acetate will not be visible. The polarising filters supplied for digital cameras are suitable for this purpose.
