Iodine

Iodine is a shiny, blue-black solid that gives off a violet vapor when warmed; its name comes from the Greek for violet. Bernard Courtois discovered it in 1811 in the ash of seaweed. Today it comes mostly from nitrate deposits in Chile's Atacama Desert and from underground brines in Japan.

Our thyroid gland needs iodine, which is why it is added to table salt, and it is a common disinfectant for wounds. In the television, iodine is soaked into the stretched polyvinyl alcohol film of each polarizer. It forms long chains along the plastic's lined-up molecules, absorbing light that vibrates in one direction and letting the rest through.