Polaroid (polarizer)

The original material, patented in 1929[1] 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 the manufacture of the film by stretching or by applying electric or magnetic fields.

The electrons moving in this current will collide with other particles and re-emit the light backwards and forwards.

[citation needed] This material, known as J-sheet, was later replaced by the improved H-sheet Polaroid, invented in 1938 by Land.

During manufacture, the PVA polymer chains are stretched such that they form an array of aligned, linear molecules in the material.