Dye Mordant - Method One.

1. Processed print film was immersed in "mordant bath", sometimes called a "mordant bleach bath" consisting of an aqueous acid solution of potassium ferricyanide that converted the silver image to white silver ferrocyanide.

A typical formula was:

• Potassium ferricyanide 2 gm per litre
• Acetic acid [glacial] 5 ml per litre

Alternative procedures were to use bleach solutions that converted the silver image to silver thiocyanate, using copper thiocyanate bleach, or to silver iodide, using an iodide/iodine bleach.

2. The film is then washed in water and dyed in a solution of basic dye. The result is a clear transparent dye image, with an additional slightly opaque image of the residual mordant salt.