DEVELOPERS, MIXED OR COMBINED Mixed developers—as, for example, hydro quinone and metol—have become popular. Developers are of two distinct kinds : (1) those that give detail quickly and density afterwards ; these include metol, rodinal, etc ; (2) those that give density first and detail gradually—for example, hydroquinone and pyro. Taking one of each class and blending, it is possible to obtain a combination of characteristics ; thus metol with hydroquinone gives detail without excessive thinness of the image or duration of development. The most is obtained with a combined developer by compounding it from one having a low factor number (see " Development, Factorial ") with one of a high factor ; and while most developers may be mixed together, there is no advantage in combining two developers of practically the same factor numbers, as, for instance, pyro and hydroquinone, both of which may be said to have, roughly, the factor of 6. A better combination is hydroquinone (factor 6) and metol (factor 3o).
The best known and most widely used com binations are hydroquinone and metol, and pyres and metal, but the following have also their advocates : Metol-adurol, hydroquinone-eikono gen, hydroquinone-pyrocatechin, hydroquinone rodinal, hydroquinone-amidol, metol-glycin, and others. Formulae for some of the best known mixtures are : Hydroquinone-Metol Metal • • • 33 grs- 3'4 g• Sodium sulphite • 99 ,, I0'2 „Hydroquinone . . 4o „ 4 If Potassium carbonate . 198 „ 20 „ Water to . . . 20 OZ. 1,000 CCS.
The above is a one-solution developer, ready for use. (See also " Metol-Hydroquinone.") Pyro-Metol A. Pyrogallic acid . 55 grs. 5'5 g• Metol . • • 45 ,, 4'5 )1 Potassium metabi sulphite . . Izo „ 12 „ Potassium bromide 20 „ 2 „ Water (boiled) to 20 oz. i,000 ccs.
B. Sodium carbonate (crystals) . 4 OZ. 200 g.
Water (boiled) to 20 „ 1,000 ccs. Use equal parts of A and B.
Eikonogen-Hydroquinone A. Hydroquinone . 4o grs. 4 g.
Eikonogen . . 120 „ 12 „ Sodium sulphite . I oz. 5o „ Citric acid . . so grs. 2 „ Water to . . 20 oz. i,000 ces,
B. Sodium carbonate 6o grs. 6 g.
Sodium hydrate . 32 „ 3.2 Potassium bromide 6 „ -6 Water to . . 20 OZ. 1,000 ccse Mix A and B in equal parts.
Metol-Glycine Glycine . . . 5o grs. 5 fl• Metol . . . 10 „ I „ Sodium sulphite OZ. 125 „ Potassium carbonate . 2i „ 125 „ Water to . . . 20 „ 1,000 CCS.
One solution, ready for use.
Edinol-Hydroquinone Water to . • . 20 oz. i,000 ccs.
Acetone sulphite . 75 grs. 7.5 g.
Sodium sulphite . I oz. ,,Edinol . . . 3o grs. 3 11 Hydroquinone . . 15 „ 1 • 5 „ Potassium carbonate . 2 oz. 100 „ Dissolve in the order named, and for over exposure add one drop of a io per cent. solution of potassium bromide to each ounce of developer used. The above is a one-solution, ready for use.
Hydroquinone-Rodinal A. Hydroquinone . 12o grs. 13'6 g.
Sodium sulphite . I oz. 54.5 „ Citric acid . . 5 grs.
•5 Potassium bromide 6o „ 6'8 „ Water to . . 20 oz. I,000 ccs.
B. Potassium carbonate 2 „ ioo g.
Rodinal 5o „Water to . 20 „ 1,000 CCS.
For soft negatives use equal parts of A and B and water. For brilliant and harder negatives use equal parts of A and B without water. For detail increase the proportion of B, and for density increase that of A.
Pyro-Arnidol Sodium sulphite . 198 grs. zo g.
Sodium carbonate . 66 „ 6.6 „ Pyrogallic acid . 20 „ 2 „ Amidol . . . io „ 1 ,, Water to . . . zo oz. 1,000 ccs.
Add the amidol just before developer is required, and it will be ready for use. It will not keep.
A durol-Metol Metol . . . 118 grs. 13-5 g.
Adurol . • • 47 ,, Sodium sulphite . 7 oz. ,,Potassium carbonate • 4'7 ,, 256 „ Potassium bromide . zi grs. 2.4 ,, Water to . . . 20 oz. Imo ccs.
Dissolve the chemicals in the water in the order named. To develop plates add 1 part of the above to 2 parts of water.
Pyro-Hydroquinone This is a mixed developer sometimes advo cated, but both agents being slow-acting and somewhat alike, it is not particularly advan tageous. It is included here chiefly because of the boric acid in the formula : A. Hydroquinone . 8 grs. -8 g.