1. The chemistry and application of dyes;Waring,1990
2. Dyes from antiquity to synthesis;Wisniak;Ind J Hist Chem,2004
3. Adolph von Baeyer and the indigo molecule;Cooksey;Dyes Hist Archaeol,2001
4. Organic chemistry in colour;Gordon,1983
5. Why is indigo blue?;Christie;Biotech Histochem,2007