TREATING WRONGLY EXPOSED PLATES.
It occasionally happens, when develop ing on the above system, that a plate will turn out to be under- or over-exposed. Over-exposure makes itself evident by the flashing up of the image immediately on the application of the developer ; it then quickly veils over. In such a case instant action is necessary. A half-plate dish con taining a 10 per cent. solution of potassium bromide is kept ready, and the plate re moved as quickly as possible to this, after a rapid rinsing under the tap. A new developer is made up, containing 2 parts of the No. 1 or pyro. solution, and only 1 part of No. 2, which contains the soda or accel erator; a few drops of bromide are also added. The plate is then removed from the bromide dish, and development com pleted with the more restrained mixture, another dish being used for the purpose. All this time, the remaining negative or negatives in the 10 in. by S in. dish arc carefully watched, or they will be over developed. For under-exposure—indicated by the image being a long time in appear ing and the slow emergence of detail— the plate is transferred to a dish contain ing a developer made up in the proportions of 2 parts of No. 1 to 1 part of No. 2 ; or
(and this is in many cases a better plan) to a developer diluted with about four times its amount of water, and containing the developer. This being ascertained, development is continued for a certain multiple of that time, when the plate is found to be of correct density. This is explained by the fact that development, with most reducing agents, proceeds in regular and definite proportion, the total time of development being always in exact relation to that taken by the first appear ance of the image. Suppose, for instance, that metol is being used, and the image a larger quantity of soda. Prints from negatives of the same subject which have been correctly, under-, and over-exposed respectively, are shown in the full page plates.