Black wash /(blăk"wŏsh)/

Black· wash

Black wash

n.
  1. A lotion made by mixing calomel and lime water. (Med.)
  2. A wash that blackens, as opposed to whitewash; hence, figuratively, calumny.
    To remove as far as he can the modern layers of black wash, and let the man himself, fair or foul, be seen.