Chromium intensifier for approximately proportional intensification of thin negatives whether arising from slight under-exposure or under-development.

Mix chemicals in order.
Potassium bichromate90
Hydrochloric acid64mililiters
Water to make1liter

Dilute 1:10. Harden the negative first in the formalin hardener. Bleach thoroughly at 18–21°C then wash until the yellow stain is removed (immersing the bleached and rinsed negative in a 5% solution of sodium carbonate for a few moments quickens this stage) and redevelop in artificial light or daylight (not direct sunlight) in any rapid non-staining developer which does not contain an excess of sulphite, such as Kodak Developer D72 diluted 1:3. The time of redevelopment varies from 3 to 10 minutes at 18–21°C depending on the degree of intensification desired. Then rinse and immerse in a fixing bath for 5 minutes and wash thoroughly.

Greater intensification can be secured by repeating the process. The degree of intensification can also be controlled by varying the time of redevelopment.

Note: Fine-grain developers of the borax type containing a high concentration of sulphite, such as Kodak Developer D76, are not suitable for re-development since the sulphite tends to dissolve the silver chloride before the developing agents have time to act on it.