The legend of the "Painted People"
Popular etymology has long interpreted the name Pict as if it derived from the Latin the word Picti meaning "painted folk" or possibly "tattooed ones"; and this may relate to the Welsh word Pryd meaning "to mark" or "to draw". Julius Caesar, who never went near Pictland, mentions the British Celtic custom of body painting in Book V of his Gallic Wars, stating Omnes vero se Britanni vitro inficiunt, quod caeruleum efficit colorem, atque hoc horridiores sunt in pugna aspectu; which means: "In fact all Britanni stain themselves with vitrum, which produces a dark blue colour, and by this means they are more terrifying to face in battle;"
Linguists generally translate the Latin word vitro as "with woad". The Latin phrase vitro inficiunt could very well have meant dye themselves with glazes or infect themselves with glass. This could have described a scarification ritual which left dark blue scars, or formed a direct reference to tattooing. Subsequent commentators may have displaced the 1st-century BC southern practices (of the Brittani, a tribe south of the Thames) to the northern peoples in an attempt to explain the name Picti, which came into use only in the 3rd century AD. Julius Caesar himself, commenting in his Gallic Wars on the tribes from the areas where Picts (later) lived, states that they have designs carved into their faces by iron. If they used woad, then it probably penetrated under the skin as a tattoo. More likely, the Celts used copper for blue tattoos (they had plenty of it) and soot-ash carbon for black. Further study of bog bodies may provide more information on the specific tattooing techniques (if any) used by the Picts.