How instant photographs work
In general, all cameras capture patterns of
light on a plastic-based film covered with particles of silver compound which
are sensitive to light. Whereas a black-and-white film only has one layer of
silver compound, a color film has three. This text will focus on the
development process of color films as they are more relevant nowadays. In order
for the film to be turned into a photograph, it has to be developed. While
common camera films are processed outside of the camera, the instant camera
film already contains the necessary chemicals.
The structure of an instant camera film sheet
Although an instant film can be bought as a
film roll, they usually comprise separate plastic sheets. To understand the
developing process of an instant photograph, it is essential to know of which
layers of chemical an instant camera film sheet is composed of. The sheet has
three layers sensitive to different colors of light: blue, green and red,
respectively. Underneath each layer, a dye developer layer for the respective
complementary colors yellow, magenta and cyan is found. All of these layers are
located on the black Base Layer and underneath the Image Layer, Timing Layer,
Acid Layer and Clear Plastic Layer. This arrangement is a chemical chain
reaction waiting to be set in motion.
Photo development in an instant camera
The reaction is set off with the Reagent. The
Reagent Layer is located between the Image Layer and the Color Layers. In
contrast to the other layers, it is accumulated at the border of the plastic
sheet, separated from the light-sensitive material. When the picture is taken,
the sheet is pushed out of the camera through a pair of rollers. Now the
Reagent is spread out into the middle of the sheet and a chemical reaction is
started. The reagent chemicals move downward through the light-sensitive
layers. Particles on the exposed color layers are changed into metallic silver.
Therefore, the respective dye layer behind them is blocked which causes the
remaining dye layers to move up to the image layer where the requested color is
created. At the same time, other reagent chemicals react with the acid layer
which finally makes the image visible. This reaction is delayed by the timing
layer to assure that the film is not exposed to light before it is fully
developed.
When the image is slowly brought to appearance
before our eyes, this chemical reaction can be observed.
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