Woad - the blue dye comes from the leaves of the plant and not the seed (crushed seed apparently gives you a pale pink dye). The initial infusion from the leaves has to have urine added to it to make a) actually fix as blue and b) fix in the cloth that's being dyed. It takes about 1 - 2 weeks to dye a piece of cloth with woad (depending on how deep a colour you want).

Some how I don't see this as a good material for painting yerself with. There may be the possibility that it was used for tattooing depending on the fixatives that they may have used. Once woad has fixed, it's apparently quite a stable colour. But the quantity needed to make the dye (and the fact that you can only use the plant at certain times during it's two year growing cycle) would have made it reasonably precious.

TTFN Lady P.