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.
Under-Exposure. An under-exposed plate has usually a lack of detail in the shadows and weakly lighted parts, with too much tendency to density in the strongly lighted portions. To counteract this as much as possible, it is best to remove the plate from the normal developer as soon as its condition is known, and, without washing, place it in a tray of water where no light of any kind can reach it. If this treatment in 2 or 3 minutes brings out the detail of the shadows where there has been but little action of light, it may then be developed in normal developer in a dark place. No plate much under-exposed ever gives a satisfactory result. It is no use to employ a large excess of alkali with the idea of "forcing" out the detail, for such proceedings will only result in fog and stain.
299. Plates or films which are under-exposed will develop slowly, and the developed negative will be thin and transparent in the shadows. If upon developing a plate an image fails to appear, the cause may be attributed to one of five things:
The slide of the holder was not withdrawn.
The shutter failed to open.
The plate was not in the holder.
The developing solution lacked an essential constituent.
The exposure was too short to give even the ghost of an image.
Under-Development. This is caused by removing from the developer too soon. The difference between a correctly exposed under-developed plate and an under-exposure is, that the entire plate of the former is thin and full of detail, instead of strong in the high-lights and thin in the shadows, as is the case with an under-exposure. The underdeveloped plate can be improved after fixing and washing by redeveloping, or in other words, by intensifying. (See instructions for Intensifying.)
Over-Exposure. An over-exposed plate is flat, wanting in contrast, full of detail but lacking in intensity in the high-lights, or foggy. Where over-exposure has occurred the image appears almost instantly after placing the plate or film in the developing solution, and the entire image develops at the same time - the shadows as fast as the high-lights - there being no contrast, no visible high-lights nor deep shadows. Over-exposure can be overcome, to a certain extent, if, as soon as a negative shows signs of overexposure, as described above, you add a few drops of bromide of potassium solution to the developer; this will restrain the development. Of course, the negative must be removed from the bath while adding the bromide. Mix the bromide well with the developer, then return the plate again to the developing bath and conclude the development. If a plate is known to be considerably over-exposed, commence with a developer containing a full dose of pyro and some bromide, but very little of the alkali, and then small quantities of the alkali may be added from time to time as the development progresses.
WINTER AFTERNOON Study No. 6 By K. T. Krantz.