Any good Elon-Hydrochinon, Kodelon-Hydrochinon, or straight
Hydrochinon formula will give satisfactory tones, though in the case
of Tone G an Elon-Hydrochinon developer is essential in order that a
rich olive color may be obtained.
For toning, it is necessary that the developed film should be
entirely free from fog, since a thin veil becomes intensified in most
of the toning processes. Fog may be caused by:
(a) Oxidation of the developer, noticeable by the brown coloration
produced after continued use. The remedy is to renew the developer.
(b) Carelessness in compounding the developer. The usual mistake
consists in adding the carbonate to the Elon and Hydrochinon without
previously adding a portion of sulphite to prevent oxidation. It
is not advisable, however, to add the whole of the sulphite to the
Elon and Hydrochinon in the first place, otherwise the Elon may
precipitate. Mixing the developer with water which is too warm will
often cause fog.
(c) The presence of copper, brass, and tin, the fumes from sodium
sulphide, etc., in the developing baths are to be strictly avoided.
A salt of copper if present only to the extent of one part in 10,000
will produce fog on cine positive film.