Bismarck brown is a product that is used in feather dyeing to a
considerable extent, chiefly in a diluted form. It dissolves readily
in boiling water. It comes in the form of a powder, of a dirty black
hue, and in liquid it is a heavy yellowish red. It makes a fast
color, alkali having but little effect on it. Oxalic or sulphuric
acid will brighten the color, and turning it more on the red order.
In giving a brownish hue to such light colors as beige, ecru, etc.,
it is invaluable. It is used by some in the topping of dark brown. It
has such a great affinity for the fibre of feathers that it is very
difficult to remove therefrom.