'Turnbull's blue' definitions:

Definition of 'Turnbull's blue'

From: GCIDE

Turnbull's blue \Turn"bull's blue`\ (t[^u]rn"b[.u]lz bl[=u]`). (Chem.) The double cyanide of ferrous and ferric iron, a dark blue amorphous substance having a coppery luster, used in dyeing, calico printing, etc. Cf. Prussian blue, under Prussian. [1913 Webster]