Before Indigo was imported from the East in the 16th Century, the only source of rich blue dye was Woad, Isatis Tinctoria, a plant which is a member of the cabbage family and which was brought to Britain by the Celts. They called it Glasto, hence Glastonbury, which means ‘a place where woad grows’.
The process by which the dye was extracted was lengthy and very smelly indeed, (think combination of raw sewage and rotten cabbage) and the people who did this work, woad dyers, were outcasts of society, since they smelt so much. As a result they were isolated and inbred. There was no way of hiding if you were a woad dyer as even if you washed yourself really well to remove the stench, the blue dye could be seen on your fingers and under your fingernails. Queen Elizabeth I, not being able to stand the stench from their workshops, decreed that woad dyers should be at least 5 miles away from wherever she was staying. As it took 50 kilos of woad in order to produce 5 kilos of pigment, the woad dyer’s job was pretty much a dawn to dusk stinking situation…
For more information on woad: http://www.colourhistory.cwc.net/woad.htm