How instant photography works

In this blogpost I am going to tell you how instant photography works. 

Basically, it can be said, that instant film follows the same principles as regular camera film. Patterns of light are captured on a plastic-based film which is covered with a light sensitive silver compound. These light sensitive silvers produce a latent image, which becomes visible during the developing process. The difference to regular camera film is that instant film already contains all the chemicals needed for developing the photograph.

The whole film is organized in layers. All these layers with the chemicals and the light sensitive silver compounds inside are attached to a black base layer. The bottom layers are the three light sensitive layers, sensitive to blue, green and red light respectively, and the developer layers containing the dye couplers. On top of these bottom layers, there lies the reagent layer.The reagent is a mixture of chemicals, which later triggers the chemical reactions. Before a photograph is taken, the reagent layer is empty and the reagent sits in the white frame, separated from the picture to prevent it from developing too early. On top of the reagent layer there are three more layers with chemicals. These are the image layer, the timing layer and the acid layer. All these layers are concealed by clear plastic on the very top. A regular colour instant film, therefore, consists of up to 15 different layers.

While taking an instant photograph, various reactions happen at the different layers of the instant film. Once you press the trigger, the instant film is exposed to light for a short moment, causing the light sensitive layers to react.The photograph then is ejected from the camera. It passes between two stainless steel rollers which spread the reagent evenly over the reagent layer. This is the start for several chemical reactions.

The reagent is a mix of different chemicals causing the other chemicals in the different layers of the instant film to react. First of all, it prevents the light from filtering on to the light sensitive layers below, so they will not react anymore. Secondly, the reagent causes the developer layers to release their dye couplers. The dye couplers then react with the different colour layers and move to the image layer, where the image is captured. On top of the image layer lies the timing layer. Its only purpose is to slow down the reagent on its way to the acid layer, giving the image time to develop. The top layer, the acid layer, clears up the particles in the reagent that prevented the light from filtering through.

When we look at an instant photograph and it seems as if it was developing right there infront of our eyes, what we actually see is just the last step. We only see the acid layer dissolving the last particles, so that the image becomes visible for our eyes.