The Photographer's Formulary Reducer I for Film is a hypo-potassium ferricyanide negative reducer. The chemicals in the kit are used to make two stock solutions.
Depending upon the relative amounts of the two stock solutions that are used to make the working solution, Reducer 1 can act either as a sub proportional or as a proportional reducer.
A sub proportional reducer removes silver metal from low density areas faster than it does from the high-density areas. This mode of removal increases the negatives contrast.
A proportional reducer removes silver metal from both high- and low-density areas at the same rate. This mode of removal improves over-developed negatives. Working solution amounts depend upon the dilution you use.