Expository text - How does instant photography work?

When I was a kid, my parents used to have a polaroid camera. They took pictures and shortly afterwards the image magically appeared. For those of you who, very much like me, have always wondered how this was even possible, here is the explanation.

Instant film or film for polaroid cameras is very similar to regular film. The main difference between the two of them is the developing process. While a regular film has to be developed externally, in a dark room, the instant film already has all the needed chemicals in its layers. Therefore, the picture develops as soon as it's been taken.

The film itself comprises of several different layers, as you can see in the image.

When a photograph is taken, the silver atoms on the film react with the light photons and create an image. In order to get a real picture, it needs to be developed. For this, rollers inside the instant camera spread the reagent layer, which is made of opacifiers (light-blockers), alkali (acid neutralizers), white pigment and other elements.

Underneath the reagent layer, there are three different light sensitive layers (blue, green and red). Under each of them lies a dye developer in its complementary color (yellow, magenta and cyan respectively). When a certain color of light reaches its sensitive layer, the opacifiers block the dye developer right underneath it. The other two developers can move up to the image layer.

This means that if blue light hits the blue sensitive layer, the yellow dye developer gets blocked. Therefore, only magenta and cyan reach the image layer, creating the color blue.

If you have ever seen an instant photograph develop, you know that it is usually greyish at first and only slowly becomes visible. This is due to the opacifiers. The reagent chemicals not only work their way down through the dye developers but also up through the image, timing and acid layer. The picture will stay greyish until the opacifiers and the alkali reach the acid layer where they react. This reaction makes the opacifiers become invisible and the picture visible. The timing layer slows the reagent chemicals down, leaving the picture underneath enough time to develop.

And voila, that is how instant films work. You see, it, unfortunately, has nothing to do with magic after all.