John W. Mollett, An Illustrated Dictionary of Words used in Art and Archaeology (1883)
“ Umber. A massive mineral pigment used by painters as a brown colour, and to make varnish dry quickly. Raw umber is of an olive brown, which becomes much redder when burnt. (See Ochres.) Umbilici, R. (lit. navels) , were the ornamental bosses which projected from each end of the staff round which a volume of papyrus or parchment (liber) was rolled. They were also called cornua, and geminæ frontes. (See Liber.) Umbo (Gr. ὀμφαλός) . (1) The boss of a shield, often sharp and projecting so as to form an offensive weapon in itself. ”
