The DARKROOM COOKBOOK, Third Edition

Photographic Reduction and Intensifi cation 129
● Intensifi cation may take place in room light.
● Negatives should be well washed and wet. If they have been dried, soak them for 5 minutes
before intensifying.
● Some intensifi ers can cause a color change to the negative which may affect printing with multicontrast
papers.
Chromium Intensifi er Chromium intensifi er is a proportional intensifi er; the amount of intensifi cation
is proportional to the amount of silver present in the negative. Therefore, denser areas of
the negative are affected more than thin areas. Chromium intensifi cation is useful for increasing
contrast since it has little effect on thin, shadow areas. To be effective, chromium intensifi -
cation must often be repeated several times.
The two main ingredients in chromium intensifi er—potassium dichromate and hydrochloric
acid—are both hazardous chemicals. Hydrochloric acid can burn a hole in your
skin, and dichromate can cause serious skin irritation. Handle chromium intensifi er with
gloves and use a respirator, observing all safety precautions (Appendix 1: Safety in Handling
Photographic Chemicals).
Instructions for Chromium Intensifi cation Two formulas for chromium intensifi cation are given in
the Formula section. Intensifi er #1 gives more intensifi cation than #2.
Negatives to be intensifi ed with chromium should fi rst be hardened either in the fi xer or
after fi xing in a hardening bath. Failure to do so may cause the gelatin to reticulate and ruin
the negative.
Immerse the negatives in the bath until completely bleached; this converts the silver
image into a combination of chloride and chromium compound. The negative is then
washed until completely free from yellow stain, about 5 minutes, and redeveloped with a
normal developer (not a fi ne-grain developer) until the image has blackened completely.
A good developer to use for redevelopment is Kodak D-72 1:3. After redevelopment, fi x
the negative for 3 to 5 minutes, and then wash thoroughly and dry. One advantage of using
chromium is that if suffi cient intensifi cation is not achieved, the process may be repeated.
Silver Intensifi cation Silver intensifi cation has a noticeable effect on low values, which is where
thin, underexposed negatives usually need help. It does, however, have the unfortunate habit
of staining everything black. Wear gloves and try not to get it on your hands or clothes, but
if you accidentally stain yourself, try using the Developer Stain Remover for Hands found
in Formulas. Instructions for silver intensifi cation will be found in Formulas: Negative
Intensifi ers: Kodak IN-5 Silver Intensifi er.
Sepia Intensifi cation Bleach and redevelop sepia toners, such as Ansco 221 Sepia Toner or Kodak
T-7a Sulfi de Sepia Toner, are more effective than chromium intensifi er and will provide maximum
archival protection for your negatives. The reason for the latter is explained more fully
in Chapter 10, Toning Prints: Protective Toners, though simply put, converting an image from
silver metal to silver sulfi de makes the image as permanent as it possibly can be.