'Black wash' definitions:

Definition of 'Black wash'

From: GCIDE

Black wash \Black" wash`\ (bl[a^]k"w[o^]sh) or Blackwash \Black"wash\, n.
1. (Med.) A lotion made by mixing calomel and lime water. [1913 Webster]
2. A wash that blackens, as opposed to whitewash; hence, figuratively, calumny. [1913 Webster]
To remove as far as he can the modern layers of black wash, and let the man himself, fair or foul, be seen. --C. Kingsley. [1913 Webster]