Step into a darkroom and discover how film is transformed into photographs

WORDS SCOTT DUTFIELD

The science of photographic film developing works similarly to how our eyes see and process images. Our ability to see comes from the interaction of our eyes with tiny particles of light called photons. When light is emitted, photons bounce off the objects around us, head into our eyes and onto photoreceptor cells. These cells send signals to the brain, which then builds an image of what we’ve seen. The developing of photographic film begins the instant a photo is taken. When a camera’s shutter ‘eyelid’ opens, light is temporarily allowed to enter the camera through the lens and hit the photosensitive film. The light leaves an imprint on the film that can be interpreted and printed by a photographer in a darkroom.

Photographic film has been in use since the early 1800s, when French painter Louis Daguerre created a process that used liquid iodine and a copper plate to create the first photographs. Since the modern era of film photography, a material called cellulose acetate has been used, which is derived from wood pulp and acid. To give the cellulose acetate its photosensitive abilities, it’s coated with a photographic emulsion that contains silver and gelatin. Like the chocolate chips suspended in cookie dough, microscopic crystals of silver halide are imprisoned in a gelatin insulator. This coating is what gives film its photographic qualities. When the crystals are exposed to photons of light, their structure changes as they obtain energy from photons. The changes in the crystals’ structure are what you see in photo film. When an object, such as a tree, bounces photons through the camera lens, its impression is captured on the film in the form of affected crystals. This is typically how black-and-white photos are produced. Colour film applies the same principles, but uses different layers of silver halides that are sensitive to different wavelengths of light, such as blue, green and red.