How Instant Photography Works

Traditional slide films used in photography consist of a plastic base that is coated with a layer of light-sensitive silver compound. Color films use three layers: one is sensitive to red light, one to blue light, and one to green light. When the film is exposed to light, each layer forms metallic silver when met with light of the right color, e.g. the green-sensitive layer forms metallic silver when exposed to green light reflected from a green shirt. Therefore, a chemical record of light and color patterns is produced. In order to get a picture from from this, a series of chemical baths containing dye developers and dye couplers has to be applied.

The paper used in instant photography consists of the same layers as traditional slide films, but there are additional layers containing all the chemicals needed for the development of the picture. The base layer is black and on top of it sit the different color layers. Under each color layer there is a developer layer with dye coupler. On the very top sit the image layer, the timing layer, and the acid layer.

A critical part for the chemical process, during which the picture will be developed, is the reagent. It consists of opacifier, alkali, and other chemical substances and is located between the light-sensitive layers and the image layer. The reagent is kept in a blob at the very edge of the plastic sheet of the paper, so the light-sensitive layers will not start to develop before they have been exposed. After taking a picture with an instant camera, the paper will come out of the camera. In doing so, it passes rollers that spread the reagent over the plastic sheet which starts the development process. As the reagent chemicals move downwards, they create metallic silver from exposed particles in each layers. The reagent also dissolves the dye couplers which then start to move towards the image layer. Metallic silver stops the dye from travelling up, therefore only dye from underneath of unexposed layers can make it to the image layer to create the picture. Meanwhile, the opacifiers and alkali in the reagent react with the acid layer of the paper. As a result, the opacifiers become clear, which makes the image visible. The timing layer is used to slow down the opacifiers and alkali, so the opacifiers will not turn clear before the image is fully developed underneath.
As soon as the opacifiers are clear, you can view your photograph!