"thing which makes (something else) black," 1570s; as "action of making black," c. 1600, verbal noun from black (v.).

(n) a substance used to produce a shiny protective surface on footwear

shoe or boot polish. As a child Dickens was employed at Warren's Blacking factory.

A practice used by certain seafarers' trades union against flag-of-convenience shipowners to compel them, by measures causing economic duress (e.g. refusing to load or discharge ships or to allow them to set sail), to sign collective labour agreements with unions with the trade union doing the "blacking". See Tetley, Int'l C. of [..]

British for Bluing;