_Tone N_—Copper-Iron-Dye Tone.
By first partially toning the black and white film (Medium) in Tone
A for three to four minutes at 65 degrees to 70 degrees F., so that
the half-tones are completely toned but the shadows only partially,
washing for ten minutes and then completing the toning process in the
blue toning bath H, the residual silver in the shadows is toned blue.
In this way a double tone is obtained, the shadows appearing dark
blue and the half-tones reddish brown.
By immersing the film toned in this manner in the Chrysoidin dye-bath
as given under Tone K, the dye is mordanted to the half-tones which
contain copper ferrocyanide, producing the effect indicated.