What is "blue verdigris"

Verdigris \Ver"di*gris\, n. [F. vert-de-gris, apparently from verd, vert, green + de of + gris gray, but really a corruption of LL. viride aeris (equivalent to L. aerugo), from L. viridis green + aes, aeris, brass. See Verdant, and 2d Ore.]

1. (Chem.) A green poisonous substance used as a pigment and drug, obtained by the action of acetic acid on copper, and consisting essentially of a complex mixture of several basic copper acetates.

2. The green rust formed on copper. [Colloq.]

   Note: This rust is a carbonate of copper, and should not be confounded with true verdigris.
   --U. S. Disp.

   Blue verdigris (Chem.), a verdigris having a blue color, used a pigment, etc.

   Distilled verdigris (Old Chem.), an acid copper acetate; -- so called because the acetic acid used in making it was obtained from distilled vinegar.

   Verdigris green, clear bluish green, the color of verdigris.