How Film Works
Film is composed of layers. Many layers. These are different for color, slide, black and white, and instant film but all contain millions of light-sensitive silver halide crystals (what we call grain) that you expose when you pop the shutter. While the other layers are crucial, for our purposes we will be looking at the light sensitive layers. Color film has three layers of silver halide: red, blue, and green.
Slide film has a few more layers than C-41:
Black and white paper is what we call “orthochromatic” which is basically a fancy word for “red blind.” This is why you can print black and white in a darkroom with the redlight on, allowing for minimal vision, whereas when printing color you must remain in total darkness. Very weird, and kind of fun. Technically you can still buy orthochromatic black and white film, but it’s not very common. Most black and white film today is panchromatic, which means it is sensitive to all colors of the visible light spectrum. The layer composition of black and white film is simpler:
You’ll notice they all have what we call an “antihalation” coating or layer, which is basically applied to the back layer to absorb stray reflecting light from the film emulsion.