Over-exposure is the most common fault of the beginner in photography. A properly exposed plate grows into a negative step by step, until the whole image, with all its delicate gradations of lights and shadows, is fully developed. An over-exposed plate acts in a very different manner. When placed in the developer, instead of the high lights first appearing and the objects coming out gradually, the whole image comes out almost at once—"flashes up" is the technical and really appropriate term. If the plate is left in the developer, the image will fade away almost as quickly as it came out, and the result will be a thin negative, from which satisfactory prints cannot be made.
TREATMENT.
As soon as the image flashes up, showing that the plate has been over-exposed, take it from the developer and place it in a dish of clean water to stop development. Turn the developer from the tray and rinse the tray. Mix up a weak solution of developer, or dilute this same developer one-third with water. Add to this weak developer a few drops of a solution of bromide of potassium, prepared with a quarter of an ounce of bromide of potassium and five ounces of water. This solution should be mixed and kept always ready for use. Label the bottle "Restrainer." The bromide is called a restrainer, as it makes the development of the image proceed more slowly.
Put the plate back in the tray, and turn the developer, to which the bromide has been added, over it, rocking the plate gently. Watch the development closely, and if the image still comes up too fast add a few more drops of bromide. Unless the plate has been very much over-exposed, by taking it from the developer and using the restrainer carefully, a good negative can usually be obtained. If the plate has been too much over-exposed, there is no way of saving it.
If one knows or thinks that a plate has been over-exposed, the plate should not be put in a normal developer—that is, a developer which would be used for a correctly exposed plate—but it should be put into the weak developer to which bromide has been added.
Some amateurs, in developing, have three trays of developer. The first tray contains normal developer, the second tray contains developer prepared for over-exposed plates, and the third for under-exposed plates.
If a plate is found to be under or over exposed, it is washed and removed to the tray containing the proper solution. This is a very good plan if one has a quantity of plates to develop which have been exposed at different times and under different circumstances, as it saves preparing fresh developer after development has been started.
Sir Knight Frank Kane asks what is meant by a flat negative. A flat or thin negative is one which has been over-exposed, and not sufficiently developed to give the necessary density, so that the light passes through all parts quickly, and gives a flat picture, wanting in contrast. The next number of the Round Table will give methods for strengthening or redeveloping thin negatives.