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.
Properly Exposed Plates Developing Slowly. As already stated, the first consideration in developing is the temperature of your developer. If the developer is cold the plate will develop slowly and thin. If the developer is diluted too much it will develop very slowly If your carbonate of soda is of poor quality, or if you have not the proper strength called for, the plate will develop slowly. You must, therefore, be careful in preparing your developer. See that your sodas are of good quality. The anhydrous or pure crystals should be used. Always buy the same brand either in bottles or in sealed packages. Another important factor is the temperature of your dark room. If it is extremely cold the action of the developer will be very slow.
Plate Flashing Up Quickly And Darkening All Over At Once, Detail Very Dim. When a plate acts like this it is a certain sign that it is over-exposed, or the entire plate has been fogged (light struck) before or after exposure.
Judging If Plate Is Under - Timed. If a plate is under-timed you will have trouble in getting it started in developing. When it finally does start, the highlights will build up contrasty, but very slowly, and the shadows will remain clear. In case of extreme under-exposure the shadows will be almost clear glass. There will be little or no detail.
Judging If Plate Is Over-Timed. If a plate is over-timed the action of the developing will be very fast. The highlights will develop rapidly, but will be closely followed by the shadows. The shadows will fill with detail, then the entire plate will appear to fog over as it were, and instead of gaining in strength will grow dim.
Producing Proper Contrast. You can only get proper contrast by being careful and developing the plates according to their exposure. If over-exposed, treat it as such or you will produce weak, flat negatives. If under-exposed and you do not treat it as such, you will produce negatives with too much contrast, strong highlights and no detail in the shadows.
Proper Color. The proper color of the negative should be on the gray order with just a tinge of brown. With the proper exposure and developer prepared according to the instructions, this is the color you will produce. If the plate is over-exposed, necessitating prolonged development, the plate will become stained a slight yellow, which, however, is not objectionable, as it will add strength to the printing quality. A thin, yellow negative will give a stronger print than one which is a blue-gray, for if a plate is extremely gray, or blue-gray, it will produce prints with weak shadows and highlights; a very pretty negative to look at, but one that will not give a snappy, brilliant print. The printing from such a negative will be very quick, so quick that the surface of the print only is affected, and when the print is washed the strength is washed away, resulting in a weak, mealy picture.