Once the normal time is known, under the experimental conditions, the times of develop ment of the same emulsion, but for other printing methods, can be obtained from the table' shown on page 262 by the aid of factors mentioned in the table by which the normal time of development should be multiplied, according to circumstances. For rapid develop ment (average time 5 min. at 6° F.) Dr. Glover recommends— Metol-hydroquinone— Metol . . . gr. (1-25 grm.) Soda sulphite, anhydrous 2OZ. (75 grm) Hydroquinone . 33 gr. (3-75 grm.) Soda carbonate, anhydrous 4 oz., (25 grin.) Potassium bromide (to% solution) 2l drm, (15 c.c.) Water, to make . 20 oz. (1.000 c.c.) For tank development (average time 30 min. at F.) the slow glycin developer is used.
Glycin Developer- Soda sulphite, anhydrous 130 gr, (15 grin.) Glycin . 90 gr. (10 grin.) Potassium carbonate, dry 400 gr. (45 grm.) Water, to make . 20 OZ, C.c.) At the time of use mix t part of this stock with 5 parts water.
388. Development by Visual Inspection of the Image. The semi-automatic and automatic methods of development which have been described (§ 384 and § 385) cannot be used satisfactorily by the cinematographer, who receives for development films of subjects very varied in character taken on films of various batches and various makes, nor by the technical photographer, who, of necessity, has to use emulsions of different types, nor by the amateur purchasing his supplies day by day and making no note of the character of the emulsions used or of the character of the subject. All these photographers must base their judgment of the point at which to stop development (at the moment considered to be right) on the appear ance of the image.
In these circumstances, often the only method of supervising development is the estimation of the degree of contrast in the negative when it is examined by transmitted light. Development is usually done in a bath of constant composition, a condition which, moreover, is imposed by considerations of economy when development involves large quantities of developing solution which have to be used to exhaustion. This would not be feasible if the bath during use were modified as regards its content of active substances. The most that can be done with this inspection method, when a plate or film comes up very unsatisfactorily, is to attempt to save it by placing it in a dish of clean water to stop development, then employing one of the special methods of development which are described later (§ 387 to § 389).
As already stated (§ 374), the judgment of the moment when the difference between the extreme densities of the negative reaches a.
favourable point demands a very long experi ence, and even then leads sometimes to mistakes, at least if one is limited to one given method of printing.
Unless otherwise stated, the developing for mulae usually published apply to this method of development by inspection.
In addition to the various formulae already given for automatic development, and perfectly adapted to the present case, a selection of other formulae are given here Maximum-energy Metol-hydroquinone Devel oper for Under-exposures I. Crabtree, 1921) to be used undiluted ; normal duration of de velopment 4 to 5 min. at 65° F. This developer will keep only for a few days, unless stored in bottles full to the neck and corked air-tight Metol . . 140 gr. (so grin.) Soda sulphite, anhydrous 525 gr. (Co grin.) Hydroquinone . . 540 gr. (16 grin.) Caustic soda . . 90 gr. (so grm.) Potassium bromide . 90 gr. (so grin.) Denatured alcohol . i oz. (5o c.c.) Water, tepid, to make 20 02. (i,000 c.c.) Concentrated Paraminopkenol Developer of the Rodinal Type (J. Desalme, 1913). Dissolve oz. (75 grm.) of paraminoplienol hydrochloride in 6 to 7 oz. (600 to 700 c.c.) of hot and filter if necessary.
Add to this solution 45 gr. (io grm.) of sodium sulphite and io gr. (35 grm.) of dry sodium carbonate, previously dissolved in 2 oz. (fluid) (200 c.c.) of tepid water. This produces a precipitate of the free base, which is filtered on a cloth after cooling. The paste is drained so that it does not occupy a bulk of more than 3 oz. (300 c.c.), and to it is added i oz. (Ioo c.c.) of liquid sodium bisulphite of density 35° Be., and then, little by little, soda lye of density 4o° Be. until the precipitate has completely dissolved. Then a very small quantity of the bisulphite is again added to obtain a persisting precipitate. Add water to bring up the total to 5 oz. (fluid) (5oo c.c.). Filter, and divide into a number of small, hermetically-sealed bottles. For use, this concentrated developer is diluted with 20 to 30 times its volume of water.
Paraphenylenediamine Developer (J. Desalme, I911)— Paraphenylenediamine (free base) 90 gr. (Io grm.) Liquid sodium bisulphite 35 Be. oz_ (fluid) (25 e.e.) Soda lye 4° Be. . (inn. (4o C.C.) Potassium bromide . . 25 gr. (3 gnu.) Water, to make . io oz_ ( i,000 c.c.) This developer oxidizes only slowly. Its keeping quality is enhanced by keeping the caustic soda separately dissolved in half the total amount of water. The developer is then prepared at the moment of use by mixing equal parts of the two stock solutions.