Copper Toning.

A red tone, more a strong red brown, was produced by generating, in exactly the same way, Copper ferrocyanide using Copper sulphate and Potassium ferricyanide. The old examples of this tone in manufacturer's example sheets are now very faded and seem just a warm neutral. It is possible that the original effect of this tone is very unlike the results we see today. Modern materials tone well by this method but we have no method of knowing whether the effect is the same as in the early years of the century.

Copper toning was recommended in early manuals but by about 1922 copper toning seems to be replaced by Uranium toning. The resulting colours were much the same but copper toning seems to leave the emulsion much softer and more liable to damage. This is true of modern print stocks - copper toning creates a nice clear warm brown image but the emulsion is very soft and easily marked.