The DARKROOM COOKBOOK, Third Edition

300 THE DARKROOM COOKBOOK
Strong Ammonium Thiosulfate Reducer
Dilute 1 part of rapid fi xer containing hardener with 2 parts of water. To each liter of the
diluted fi xer add 30.0 grams of citric acid, anhydrous.
This dilution is useful for reducing high-speed negative materials. The reaction is very slow
and will depend on the specifi c emulsion and the degree of reduction desired.
NOTE 1: Before reducing a negative or print clean thoroughly with fi lm cleaner to remove
any surface grease left from handling. To promote uniform reduction pre-wet the emulsion in
a wetting agent such as Edwal’s LFN.
NOTE 2: Possible sulfurization of the fi xer can be avoided by dissolving the citric acid in a
portion of the water used for dilution.
Caution: This reducer gives off a strong odor of sulfur dioxide and should be used in a wellventilated
room. Do not use near sensitized photographic products.
FORMULA #168
DuPont 4-R
Eder’s Harmonizing Reducer
This reducer acts in a unique fashion, intensifying lighter densities and reducing the heavier
densities. It is useful for correcting excessive contrast.
Bleach solution:
Water, 750.0 ml
Hydrochloric acid, concentrate, 30.0 ml
*Potassium bichromate, 10.0 g
Alum, 50.0 g
Water to make 1.0 liter
* Potassium bichromate is an allergen to some people and a suspected carcinogen. See precautions
under potassium bichromate in Pharmacopoeia.
Bleach to completion. Wash thoroughly until the yellow stain has disappeared. The
removal of yellow stain is accelerated if after a 2 to 3 minute wash the negative is immersed
in a 2% solution of sodium bisulfi te for a few minutes and then returned to the wash.
Redevelop in a slow-acting developer, such as D-23 diluted 1:5, then fi x and wash in the usual
manner.
Caution: Always add the hydrochloric acid to the water slowly, stirring constantly, and never
add the water to the acid.