The DARKROOM COOKBOOK, Third Edition

184 THE DARKROOM COOKBOOK
Caution: Metol has a reputation for causing skin poisoning (a painful rash that looks and feels
like poison oak). It includes severe itching, red rash, and peeling skin. This poisoning usually
occurs after being exposed to the substance over a period of years but in some cases can
happen even sooner.
It is believed that metol poisoning results from trace contamination of para-phenylenediamine
(ppd) in the metol, not from the metol itself. Knowledge of this has changed the
manufacturing process, and as a result, metol poisoning is less common than it once was.
Good-quality metol does not usually cause a rash. However, some people are still sensitive
to even the purest grade of metol. It is possible to avoid metol poisoning either by wearing
protective gloves or by substituting Phenidone.
MONOMETHYL PARA-AMINOPHENOL SULFATE (see Metol)
6-NITROBENZIMIDAZOLE NITRATE (see Antifog No. 2)
ORTHO-PHENYLENEDIAMINE (opd)
Formulas: 1,2-Benzenediamine, ortho-Diaminobenzene, para-aminophenol hydrochloride.
Appearance: White to brownish-yellow crystals.
Uses: As a fi ne-grain silver solvent; a substitute for p-phenylenediamine; or very weak developing
agent. Usually used in combination with metol.
(see para-Phenylenediamine)
PARA-AMINOPHENOL HYDROCHLORIDE
Formulas: 4-Amino-1hydroxy-benzene hydrochloride; para-Hydroxyaniline.
Trade Names: Activol, Azol, Kodelon (Kodak), Para, Rhodinal.
Appearance: White, crystalline substance.
Uses: As a developing agent used in conjunction with sodium or potassium carbonates or
with caustic alkali. The sodium salt of this is the developing agent in the concentrated solution
of prepared developer. It is marketed under the trade name of Rodinal by Agfa.
Notes: At one time this was a very popular developing agent. In 1931 the Eighth International
Congress of Photography adopted as a standard developer for scientifi c sensitometric work
the following formula:
para-Aminophenol hydrochloride, 7.25 g
Sodium sulfi te, anhydrous, 50.0 g
Sodium carbonate, anhydrous, 50.0 g
Water to make 1.0 liter
p-Aminophenol hydrochloride is very soluble in cold water. Its principal use is in the
preparation of very concentrated developers with caustic alkali that could be diluted from 20
to 100 times. Concentrates keep well and should not be diluted until immediately before use.
These developers work rapidly, are free from fogging properties, and do not stain. They
are not sensitive to temperature variations, nor do high temperatures affect their clean