History of whitening.

Man's earliest endeavours to enhance the brightness of white objects in everyday use, especially clothing, led to the invention of various bleaching processes. KRAIS'S discovery in 1929 that the natural substance esculin could be applied to textiles to give whites of unprecedented brilliance led to the industrial development of fluorescent whitening agents (FWA's). The limited effectiveness of esculin, a glycoside of 6,7-dihydroxycoumarin prompted research which led to the synthesis of other compounds of the same class, many of which have proved useful as whiteners; though the really broad developments of the 1940's stemmed from the synthesis of the 4,4'-diaminostilbene-2,2'disulfonic acid derivatives which are sill the most important groups of FWAs.