REGISTRATION OF PHOTOGRAPHS (See " Copyright.") A method of converting into a haloid salt the silver which forms the image of a negative, and then, by re-development, obtaining a negative of, if required, reduced density compared with the original. One of the most simple and satis factory formula is : Potassium ferricyanide 8o grs. 18 g.
Potassium bromide . 120 „ 27 Water . . . zo OZ. 1,000 ccs.
The negative is immersed in this solution until the image is thoroughly bleached, as in mercurial intensification, and then well washed for about twenty minutes. It is now ready for re-develop merit Any developer may be used. The plate must be exposed to light after bleaching ; but exposure during the washing will be found suffi dent. If the negative is fully re-developed, the re-halogenised plate will be practically unchanged from its original character. But shorter develop ment will naturally convert only a portion of the haloid salt into metallic silver, thereby pro dudng a negative possessing less density than the original. It is somewhat difficult to judge the
degree of strength produced, although the de velopment is carried out in white light ; the unchanged haloid adds so much to the apparent strength in the early stages of development. The time will assist in judging the proportion of the silver salt developed into metallic silver ; the full time would be the same as that originally occupied in development. After re-development, fixing is necessary in the same manner as with an ordinary negative.
The only change that can be effected by this method of working is reduction of density, and this takes place uniformly throughout the scale. The re-halogenised plate may be afterwards intensified or reduced by any other method.