Foma produce a 2-part sepia toner based on thiourea. First a fully processed & well washed print is bleached in a ferricyanide toner. Most of the image vanishes at this stage as the silver of the image is converted back into silver halide salts. After washing the print is then ut into the toning bath, where it rapidly re-appears, but now converted into yellow-brown silver sulphide, which views as a sepia colour.
The degree of warmth can be controlled by altering the bleaching time. Partial bleaching will reduce the warmth of the sepia & by retaining silver in the shadows will give a more solid black.
Fomatone Indigo comprises concentrates for making a single solution blue toner. Using ammonium ferric citrate, a blue prussian blue image is formed when used with well washed prints. The degree of colour can be controlled by the time of toning.