This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
426. The various developers mostly show in their character considerable variation. Each has its special merit, which makes it suitable for a particular work. In order, therefore, to combine developers of these special properties, the various developers can be applied in a mixed form, and a great deal of use is made of such processes.
427. For these combinations metol and hydro qui none, and metol and adurol, are those which deserve the greatest attention, and have, consequently, found the most use. These combinations are distinguished from all others in a remarkable manner, as the properties, or the components, do not simply combine, but they also increase considerably in efficacy. For instance, metol - hydroquinone works with greater energy than metol alone, and gives more density than hydroquinone alone. The reason for this is that when combining metol and hydroquinone it is not simply a mixture, but at the same time in the alkaline solutions, an actual chemical combination takes place, which again possesses other properties than the components. The fact that metol - hydroquinone develops more quickly than metol and gives more density than hydroquinone, makes it preferable in some instances for use in the studio and for instantaneous photography, as it permits in both cases of shorter exposure, and works more rapidly.
428. Metol - hydroquinone, in its class, is the most popular developer of the day, and forms the main substance of nearly all the ready solutions which are on the market. It is the most popular developer for developing papers, and for obtaining clean black tones on bromide paper it is unsurpassed. For negatives, especially lantern plates, it is probably the most used developer, outside of pyro.
Metol - Hydroquinone Developer. Being a very rapid developer, will completely develop a plate, or film, in from two to six minutes. It is recommended for lantern slides, and film developing in particular, but serves as a good plate developer as well. The color of the negative is inclined towards a blue-gray, and, therefore, plates other than lantern plates developed with this bath should be carried a trifle further in development than if developed with pyro, for the pyro gives a brown colored negative which produces vigorous prints, even from a thin negative. While the metol giving a blue - gray negative, if developed thin, will produce flat prints, where if carried a little further in the developing, better prints will result. For lantern slides the blue-gray tone is preferred, and therefore this combination serves as a good developer. Any result may be obtained by manipulating the developer. Certain rules must be observed, however. Deep black tones can only be obtained with short exposures, and strong developers (concentrated solution, and little bromide) ; warm tones going into brown can be obtained with longer exposure and retarded development ( diluted solutions, little alkali and much bromide of potash). The best plan is to follow the instructions given with each kind of lantern plates. It must be observed that with a long duration of development of the lantern plates the plate will become colored, and it is, therefore, important that you develop quickly; two to three minutes is best. Underexposed images are best discarded, generally speaking, especially for obtaining black tones.
430. Metol, to some users, is poisonous and therefore objectionable. Many however are using metol developer without any ill effects whatever, and for those who can use it they will find the formula stated herein to give very good re-suits: -
Metol - Hydroquinone Formula.
Sulphite of Soda (Anhydrous)
Carbonate of Soda (Anhydrous)
5 1/2 ounce
Dissolve the chemicals in the order indicated in the formula, and for use prepare as follows:
To every ounce of this concentrated Stock Solution add eight ounces of water, making nine ounces of solution. One-half of this amount is sufficient for the developing of a 4 x 5 plate.
431. If the factorial method for developing is employed with this combination formula, you will find ten as the factor, and it will completely develop plates in six minutes, and for tank development, by substituting ten ounces of water to every one ounce of concentrated stock solution, you will have an eight minute developer. Slow development with this metol formula is very apt to produce fog; therefore the best results are obtained when development is completed within eight to ten minutes.
432. Metol - hydroquinone keeps better, and consequently is more economical than other developers. The solutions can be used until entirely exhausted. The following are a few additional formulae that will give good results, and are particularly good for lantern plates: -
No. 1. A Two - Solution Metol - Hydroquinone Developer.
Sulphite of Soda (Crystals) .
5 1/4 ounces
If Anhydrous Sulphite is used, use 3 ounces.
Carbonate of Potash.............
3 1/2 ounces
Note. - Carbonate of Soda may be substituted for Potash, as follows : -
Carbonate Soda (Anhydrous).. .
Or Carbonate Soda(Crystals)
433. The metol and hydroquinone must be dissolved before the sulphite of sodium is added. For use take one part A, one part B, one part water, and add, as required, from five to fifteen drops bromide of potassium. It is also permissible to originally add to this Solution B a few drops of bromide of potassium, as it will do no harm. The temperature for development should not exceed sixty-eight degrees Fahr. Duration of development from three to four minutes. The previously used developer can be employed repeatedly.
No. 2. Metol - Hydroquinone One - Solution Developer.
Sulphite of Soda (Crystals) ..
5 1/4 ouncs
Carbonate of Potassium.....
5 1/4 ounces
Bromide of Potassium......
Note. - If Anhydrous Sulphite is used in place of Crystals, use three ounces.
Carbonate of Soda may be substituted for Potash, as follows:
Carbonate of Soda (Anhydrous). ,
Carbonate of Soda (Crystals)...
434. The metol and hydroquinone must be dissolved before the sulphite of soda is added. For use take one part solution to three parts of water. The temperature for development should not exceed sixty - eight degrees Fahr. The image, when applying this developer, will appear almost instantaneously, and development is completed in about three minutes. The used developer can be employed repeatedly.