Instant Film Explained

If you’re a baby boomer, when you were a child, it’s likely that your family owned a Polaroid camera. For special events like birthdays and graduations, Dad would pull out the Polaroid and take a few shots. Then everyone stood around anxiously waiting to see how the photos turned out. Let’s explore what made those pictures mysteriously appear on the paper.

To understand instant film, it’s good to understand basic film processing first. Standard film is a strip of plastic coated with compounds containing silver halide. Color film has three layers, each sensitive to a different color spectrum of light – red, green, and blue. When you expose the film by opening the shutter of the camera to light, the chemicals in each layer react according to their sensitivity and create a record of the pattern of light and color that the camera “sees.”

To turn the exposed film into a negative, you have to process the film using dye developers that match the light colors to complementary dye colors of cyan, magenta, and yellow. The developing solution turns the silver halides into metallic silver and creates areas of dye concentration corresponding to the amount and density of the colors on the exposed film. The bleaching step turns the metallic silver back into silver halide, and the fixing step removes the silver and stabilizes the dye colors. Finally, the film is rinsed and dried.

In order to create a print from the negative, you must use color printing paper that also has an emulsion coating which reacts to the colors in the negative to produce a finished photo. The developing steps are similar to those for the film itself.

In an instant camera, the steps are combined. Instant film layers the silver halide emulsion for exposure of each light color with the dye developing emulsion for the same color just below it.

The print from an instant camera is a thick, stiff paper with a sort of pocket of chemicals to one side. The pocket contains a reagent chemical including light-blockers and acid neutralizers. After the shutter has exposed the print to light, the print ejects from the camera past a set of rollers that spreads the reagent from that pocket onto the print area to begin a chemical reaction that creates the picture.

If you separated the layers of the instant print you would find the light-sensitive image layer at the top, a reagent layer, six layers of emulsion – each color layer above its corresponding developer layer, and a black base layer at the bottom.

Once the reagent is applied by the rollers, the developing layers begin doing their work, releasing the silver and forming the dye patterns that correspond to the photo image. While this is happening, the neutralizers in the reagent gradually begin to make the light-blockers turn clear. This is when you begin to see the image developing on the paper. If the light-blockers weren’t there at the start, the entire print would be exposed before the dye developers had a chance to create the picture.

With the shift to digital photography, with all its flexibility and power, instant photos have a new meaning these days. But once upon a time, instant photos seemed like a small bit of magic.