The Romans used indigo

… for painting, medicine, and cosmetics.  It was imported to the Mediteranean from Arab merchants.  It was rare in Europe, where the chemical “twin” dye woad (“Isatis tinctoria”) was used instead. Late in the 15th century, Portuguese explorer Vasco de Gama found a sea route to India, which led to …

In Europe, woad…

… a plant containing similar chemicals was used for dying things blue, but these and others had low concentrations which make them difficult to work with and the color is more easily miscolored by other chemicals which often leads to a greenish tinge to the blue. The “Indigofera tinctoria” consistently …

Indigo actually came from different…

…plants through history, but most came from the “Indigofera” plant genus, which are native to the tropics and specifically from India.  Another species called “strobilanthes” from Japan’s Ryukyu Islands and Taiwan produces indigo. Dyer’s knotweed (“polygonum tinctorum”) was the most important blue dye in East Asia until  the “Indigofera” was …