Woad and it's mis-association with Pictish BodyArt
Julius Caesar brings the next evidence in with his description in the Gallic Wars book V. But this information has been a moot point for antiquarians as you will see." All the Brittani, indeed, dye themselves with woad, which produces a dark blue coloring." Has been the common translation of," Omnes vero se Britanni vitro inficiunt, quod caeruleum efficit colorem."
The debate comes from there being no mention of woad as the causative agent and a second better rendering of the quotation would be "dye themselves with glazes." There is also the possibility that it read "infect themselves with glass" which could have been a description of a scarification ritual which left dark blue scars. Or a direct reference to tattooing. Thats without starting the argument about how the Picts were named.
These 1st century southern practices (of the Brittani, a tribe south of the Thames) have been placed upon the northern peoples in an attempt to explain the name Picti which came into use only in the 3rd century. The comments on the tribes from the areas of the actual Picts from this section of the Gallic Wars are that they have "designs carved into their faces by iron". Ouch, that's hardcore.
The Pictish culture of north eastern Scotland had survived the celtic insurgence of 450BCE and the Roman invasion and expansion to retain a separate language and architectural heritage. They are the builders of the forts that stud the east by the thousand. The builders of the duns and brochs had separate cultural identities but their positions far to the west and north respectively, removed them from the reach of roman pen and classification.
So what's my point you may ask?
Well it's this, after my experiments and research on woad and the short comings of it as a body dye, I'm still in love with the idea of it. I've come to the conclusion that 'if' it was used (and it is only later writers, not Julius Ceasar who talk of it) then it was probably tattooed under the skin.
Update: Here's what the exceptionally well informed traditional tattooist Pat Fish thought about the previous paragraph:
...(woad) is also an amazing astringent. The tattoo I did with it literally burned itself to the surface, causing me to drag the poor experimented-upon fellow to my doctor who gave me a stern chastizing for using innappropriate ink. It produced quite a bit of scar tissue, but healed very quickly, and no blue was left behind. This leads me to think it may have been used for closing battle wounds. I believe the Celts used copper for blue tattoos, they had plenty of it, and soot ash cardon for black. Unfortunately we need more bog bodies to prove this point!
So I can now only asume that woad was used merely for dyeing fabrics and the bodyart of the Ancient Britons utilised a medium other than woad.