Dye Mordant - Method Two.

1. Processed print film was immersed in uranium nitrate toner solution as described above for about 2 minutes by which time the image had faded to a light brown.

2. The film was briefly washed before being dyed in the dye solution. Apparently, this very effective process gave good results without too much loss in contrast.

Trying to identify which method was used, not to say which dye was used, is extremely difficult. Several early textbooks give lists of dyes suitable for mordant toning and paper prints were still being toned using this method until at least 1950.