Instant
cameras were a real revolution in the world of photography. Their invention made
it possible for people to take a picture and hold the actual photograph in
their hands only a few seconds later. How does that work? The film inside the
camera is a plastic base coat with particles of silver compounds that are
sensitive to light. Color films, such as those in instant cameras, have three layers
of silver compounds – the top layer is sensitive to blue light, the middle
layer to green and the bottom layer to red light. Underneath each layer, there
is a developer layer containing dye couplers. All these layers sit on top of a
black base layer and underneath the image layer, the timing layer and the acid
layer. When exposed to light, the sensitive particles at each layer react to
light of that color, forming metallic silver at that layer. The developing
process is then started by the reagent. It is a mix of light blockers, alkali and
white pigment. It is collected in a blob at the white bottom of the film sheet,
away from the light-sensitive material to keep the film from developing
before it has been exposed. After taking a picture, the film sheet passes out
of the camera through a pair of rolls. The rolls help spread the reagent out in
the middle of the film sheet where it reacts with other chemical layers in the
film. The opacifier material stops the light from filtering onto the layers
below. The reagent then dissolves the developer dye so it begins to diffuse up
toward the image layer. Only the dyes from the unexposed layers will reach the
image layer. The acid layer in the film reacts with the alkali and opacifiers
in the reagent, making the opacifier become clear. The timing layer slows the
reagent down on its way to the acid layer, to give the film time to develop
before it is exposed to light. When the film sheet gets out of the camera you
are actually able to see the last chemical reaction, namely the acid layer
clearing up the opacifier in the reagent and making the image visible.
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