Brewer's: Æson's Bath
Sir Thomas Browne (Religio Medici, p. 67) rationalises this into “hair-dye.” The reference is to Medea renovating Æson, father of Jason, with the juices of a concoction made of sundry articles. After Æson had imbibed these juices, Ovid says:
Barba comæque, Canitie posita, nigrum rapuere, colorem.
—Metamorphoses, vii, 288.