Polaroid Originals produces an online magazine which this month features a piece on the chemistry behind the Polaroid print. A presentation recorded on SoundCloud features a 15 minute or so in-depth talk by Polaroid Originals Scientist and CTO: Stephen Herchen. Stephen describes the make up of an integral Polaroid print, the chemistry behind the development process inside the print and the magic pod of chemistry at the bottom border of every Polaroid print.
An integral Polaroid print consists of 12 layers on the lower part of the print, an air gap between that and a transparent sheet of plastic at the top, which in turn has 4 layers coated on the inside of it. Of the 12 layers, 3 are colour sensitized silver crystal layers, much like any colour film. Below each silver halide layer are colour dyes.
These dyes use the subtractive colour model to produce the final colours in the print. When a particular colour of light coming into the camera activates one of the colour sensitive silver crystals, that crystal pins down the dye that is below it. e.g. If red light from a subject, such as an apple, strikes a red sensitive silver crystal, the cyan dye below is pinned by the development process. The red light does not activate the green sensitive or blue sensitive silver layers. So in development, the magenta and yellow dyes are then freed from below the green and blue sensitive layers. The dyes then combine and diffuse to the top layer to make red in the final print. (Combining yellow and magenta makes red.)
In fact, there are more than 50 chemical processes involved in the development of a Polaroid. One of the most important components in the developer pod is an opaque dye that covers the sensitized silver layers as the print is ejected from the camera. This protects the print from exposure to any further light while one of the most complex man-made chemical processes does it work. One of the last steps of the carefully timed chemical reactions is to make that opaque layer transparent. Then, voila, a developed print.
