Iridescent inks are widely used on most high security documents, such as passports, banknotes and visas.
They are manufactured with very special pigments providing a change of colours with a very efficient flip-flop effect; they are almost transparent under a 90° view angle and coloured under a 45° angle.
They are very usefull against colour photocopies because their appearance change totally between the original and a photocopy.
Various colours are available for flexography, silk-screen and gravure, but offset or letterpress cannot be used with those inks. With flexography the deposit must be important with a minimum of 15 to 20cm3/sqm.
Iridescent inks can have also 2 colours, for example red and blue, or green and blue, or green and gold.