Caesar - "All the British color themselves with glass, which produces a blue color."

"Vitro" translates to a type of blue-green glass that was popular among the Romans, it does not translate to woad. Most authors accepted it as woad though, as woad was used to dye cloth blue at that time.

The only other evidence given is Pliny the Elder's discussion of women's funeral rites that involve using a "Glastum" a "plantain-like" plant to paint themselves to look "like Ethiopians." Also assumed incorrectly to be woade.