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.
Library by the Seed Dry Plate Company.
642. Without going into a scientific explanation of the chemical action of the light on the exposed plate, we know that the plate exposed in the camera bears a latent image of various light intensities which must be made visible by development.
643. Intelligent development necessitates a knowledge of the purposes of the various component parts of the developer.
644. First, we have the developing agent proper (Pyro-gallic Acid, Metol, Hydroquinon, Eikonogen, or other preparations of a similar nature) which, in solution, in a process of oxidization, reduces to a metallic form the silver in the emulsion that has been acted upon by the light. Carbonate of soda or other alkalies increase the affinity of the developing agent for oxygen, and also serve the double purpose of opening the cells of gelatin wherein lie the particles of silver to be acted upon, and this action is slow or rapid in proportion to the amount and quality of the alkali used.
645. The rapid oxidization of the developing agent by the alkali needs a corrective agent which we find in sulphite of soda, which also seeks oxygen, and, used in proper proportion, controls the color of the resulting image.
646. Without the sulphite the negative would be yellow and stained, and as yellow is a non-actinic color, if development were carried to a proper point of density, the highlights would be absolutely incapable of transmitting light, and the resulting print would be chalky white except in the deepest shadows.
647. The action of sulphite of soda is to eliminate this color to a greater or less degree, and the amount used regulates the color, bringing it to the point desired.
648. If too much sulphite be used the resulting negative is blue-gray in color and as this color readily admits the passage of light, the resulting prints are apt to be flat and lacking in brilliancy, unless development is carried to a point of density where many of the higher tones of light run together and are lost. The most desirable color, therefore, in a negative is a warm black with a slight tinge of yellow through the image, keeping in mind that color is equivalent to density, and currying development only to the point where the highest lights are sufficiently transparent to print detail.
649. This character of negative prints quickly, and if proper balance has been observed in lighting, it will be found the most satisfactory quality for printing in any medium. With a proper understanding of the purposes of the chemicals going to make up the developer it is easy to understand the necessity of maintaining a harmony of arrangement of the component parts, and to adapt them to the conditions under which one is working.
651. Many impure carbonates of soda contain caustic soda or caustic potash, which are most active alkalis, and being an unknown quantity will produce an alkaline action that one cannot provide for. Impure sulphites too are apt to have an indefinite amount of alkali, causing uncertain and variable action.
652. Seed's sulphite and carbonate of soda obviate these uncertainties, as they are always pure and uniform in quality, and once they have been adjusted to produce the required quality of negative they can be depended on to give uniform results.
653. As to the various developing agents in use, each has its peculiar merits according to the manufacturers, and all are good, either separately or in the various combinations of Metol-Hydro, Eikonogen-Hydroquinone, Pyro-Metol, etc., as given in the formulae following.
654. Pyro, however, seems to hold its own with the professional photographer owing to the printing color which it gives and the ease of its manipulation.
656. The dark room and solutions should if possible be kept at a temperature of sixty-five to seventy degrees Fahr., and the developer should never be permitted to go above seventy degrees in summer, or below sixty-five degrees in winter.
657. Too cold developer in winter produces thin negatives with an appearance of being under-exposed and this effect is also due frequently to plates being kept in a very cold room where they become chilled.
658. Too warm developer, particularly in summer, produces a heavy, flat quality in negatives, lacking in gradation and atmosphere, due to a swelling of the minute cells of gelatine and running together of the deposit of silver. Every dark room should be provided with a thermometer, and solutions tested before developing.
660. Tank development has its advantages in this regard asthe developer being in a compact body, with such a small surface exposed to the air, does not change so rapidly in temperature. Any of the following formulae can be adapted to tank development by the addition of more water to slow the action and a corresponding increase of sulphite of soda to correct the additional color that comes from prolonged development.
661. Certain control is possible in development, particularly if the exposure is known to be over or under the normal, before development begins.
662. The addition of a few drops of ten per cent, solution of bromide of potassium to the developer and a decrease of the alkali will correct to a great degree an exposure that is very much above the normal. If, however, development has begun before it is discovered that the plate is over-exposed, the developer should be washed out of the emulsion, and the plate immersed in old developer containing bromide. If this does not bring proper balance of highlights and shadows, development should be carried beyond the normal point and the plate reduced with red prussiate of potash (ferricyanide of potash).
663. In known under-exposures of portrait, or pictures made in a low key of light, add two or three times the normal amount of water (warm if in winter) and a slight increase of alkali, and develop till the detail is well out in the shadows; then complete development in normal solution.
664. If a plate shows under-exposure after development begins, take it from the developer and without rinsing it lay it in a tray of water, repeating the process until the detail is well out, and then proceed in normal solution to the required density.
The foregoing applies to indoor exposures.
665. Paradoxical as it may seem, we would recommend opposite treatment for instantaneous outdoor exposures. When this character of exposure is under-timed use less than the normal amount of water and a material increase in the alkali.
666. The point of complete development is often a matter of uncertainty with photographers, largely because of the lack of attention to the temperature of solutions, as negatives will appear to reduce very much in the fixing if developed in cold developers, or the reverse if developed in warm solutions.
667. Another cause of uncertainty in this regard is working in too weak a developing light.
668. The dark room light should be of good volume so development can be judged up to the last stage.
669. There is no light absolutely safe, but a combination of ruby glass and transparent post-office paper will be safe, in which to examine plates after development has begun, and should be sufficient volume to enable one to read a newspaper at a distance of two feet from the light.
670. If the quality of the light is correct the quantity need cause no alarm. With this kind of developing light, and provided temperatures are approximately correct, it becomes only a matter of experience to be able to judge the density of negatives during development.
671. Complete development of the negative is reached when all the various light intensities of your subject are recorded in their relative values, and the highlights have reached the limit of density through which you can print detail without obscuring the shadows.
672. There is no rule that can be laid down for determining when this point is reached. Practice, only, will educate the eye to correct judgment of complete development.
673. To our amateur friends whose subjects and exposures vary greatly, we offer the factorial system of development by Mr. Alfred Watkins. The theory of the system is that no matter what the exposure, development proceeds at a regular rate. The time of appearance of the first highlights of the image is a definite fraction of the time in which development is completed.