Polaroid (polarizer) Polaroid (polarizer) Polaroid is a type of synthetic plastic sheet which is used as a polarizer or polarizing filter. A trademark of the Polaroid Corporation, the term has since entered common use. The original material, patented in 1929 and further developed in 1932 by Edwin H. Land, consists of many microscopic crystals of iodoquinine sulphate (herapathite) embedded in a transparent nitrocellulose polymer film. The needle-like crystals are aligned during manufacture of the film by stretching or by applying electric or magnetic fields. With the crystals aligned, the sheet is dichroic: it tends to absorb light which is polarized parallel to
Polaroid type 55 series film) requires a Polaroid Model 545 Film Packet Back. This is mounted onto the back of a camera, usually a large format 4x5 inch type, in place of a conventional film carrier. A self-contained waterproof transparent sleeve containing positive and negative film sheets and a small reservoir of reagent gel is inserted into the Packet Back, an exposure made and the Packet Back is removed. By flipping a lever and withdrawing the sleeve the gel is squeezed between the negative and positive emulsion layers. After the set time the layers can be peeled apart. some gel is retained at