Polaroid Instant Cameras: The Secret Is in the Film
All cameras function in the same way--they capture patterns of light (what we see as images) on plastic-based film covered with a silver compound. When you take a photo, the shutter opens briefly to capture the image the lens "sees" and imprints it on the film's silver compound. Color film has three layers of silver compounds, each sensitive to different hues of light: blue, green and red. In order for the film to be turned into an actual photograph, it has to be developed. The secret to Polaroid Instant Cameras is in the film: The film itself already contains the chemicals necessary for photo development, whereas regular cameras need their film to be processed separately, outside of the camera.
Photo Development Chemicals in Polaroid Film
Beneath each of the three silver compounds that are respectively sensitive to blue, green and red light, there are four special chemicals waiting to react: the developer layer, image layer, timing layer and acid layer. These four chemicals are set off by a "reagent." Before a picture is taken, the reagent is set along the white plastic border of the Polaroid film, away from the silver compound.
Chemical Reactions Make Photos
After you snap a picture and capture the image on the silver compound, the Polaroid film is spit out through two rollers that smoosh the reagent on the white plastic borders onto the silver compound. The reagent causes the four special chemicals (developer layer, image layer, timing layer and acid layer) to react, causing the silver compound layers to process--thus producing blue, green and red light patterns, which result in an images. When you first see a Polaroid image come out of the camera, the photo itself is still gray. As the image appears slowly before your eyes, what you're actually seeing is a chemical reaction: the special chemicals reacting with the silver compound.