In some old processes, the film emulsion was hardened during the process, typically before the bleach.
Today we have better film emulsions, printing papers and developers than were available in black-and-white's heyday.
If used with modern film emulsions, the results can be very good.
The design means there is no waste of film emulsion for the targeted aspect ratio.
Different layers of the film emulsion respond differently to lower light levels, and choice of film can be very important.
To make matters worse, many objects' spectra do not line up with the film emulsion's sensitivity curves.
The film emulsion at the time had limited sensitivity and skies would often have little to no detail.
The fastest and most sensitive film emulsions available to photographers need about 25 times as many photons in order to detect a point of light.
Advancements in film emulsion and grain structure provided a wide range of available film stocks.
It uniquely identifies the type and manufacturer (sensitizer) of a film emulsion.