This formula is recommended because it is convenient in use and gives permanent results. The degree and character of intensification can be controlled to an extent by modification of the developing time used for the redeveloper.
|Potassium Bichromate||9 g|
|Hydrochloric Acid||6 ml|
|Water to make||1 L|
Immerse negatives in this solution until bleached, wash for 5 minutes in running water, and develop in bright but diffused light in a metol-hydroquinone developer such as Ansco 47. Negatives should then be given a 15-minute wash before drying. Intensification may be repeated for increased effect.
If any blue coloration of the film base is noticeable after intensification, it may be easily removed by washing the film for two or three seconds in water containing a few drops of ammonia, in a 5% solution of potassium metabisulfite, on in a 5% solution of sodium sulfite. This treatment should be followed by a through washing in water.
From Ansco Formulas for Black and White Film by GAF, 1948 – Formulas are provided for historical reference. They may not work well with modern films and papers. Some of the chemicals can be dangerous. As with all photographic processes, be careful.