I would guess that is the dust burning off the elements over the years.
silver halides
Negative photographic film; both black and white, and colour; are both opaque before they are developed. After development, they are transparent, translucent, or opaque depending on the part of the photographic image.
the film . .
DRF is a photosensitive resin in a multilayer configuration with a carrier film and cover film. DRF thickness is the carrier film thickness.
Photographic film is a type of film used in cameras. This film has one side with transparent plastic coating and the other covered with light-reflecting crystals of silver halide.
Black Out - film - was created in 1970.
The duration of Black Out - film - is 1.53 hours.
Black Rage - film - was created in 1972.
Black Film Review was created in 1984.
Black Sun - film - was created in 2005.
Penny Black - film - was created in 2013.
Black Cadillac - film - was created in 2003.
Black August - film - was created in 2007.
Black Jack - film - was created in 1950.
Black Roots - film - was created in 1970.
Black Fist - film - was created in 1974.
Black Dahlia - film - was created in 2006.