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1035 —
of the principal image of reduced silver. Indeed, the grain of the image is in relation with that of the emulsiun of bromide silver while it is permissible to believe that the formation of the secondary image is produced particulary on the surface of the grain and tends to eliminate the transparency.
However this may be, it is important to state that the attenuation of the grain which is demanded to-day in development baths, representing a minimum of alkalinity and an abundance of alkaline sulphite, may be obtained by a diametrically opposed process, that is to say, by strong alkaline baths without sulphite. The question is worth studying.
Intensification of the Negative Image by the Accumulation of Secondary Images.
Among intensifiers the only one that does not demand the use either of salt, mercury or metal ferrocyanide is that which has been studied by Lumiere and Seywedetz, which utilises chlorochromates.
By this method which we will not describe here, it is made possible to add to the silver image a deposit of oxide of chrome which enhances to a certain extent the opacity of the image. But if the bath of pyrocatechine with caustic
alkali and without sulphite is used, a better result is obtained by means of a simple application of brome to the image without re-development. This application is made with the usual solution of bromide of potassium and red ferrocyanide. The operation may be renewed several times, enhancing the opacity of the image, but after some treatments the clearness and transparency deteriorate.
The alkaline bath of pyrocatechine without sulphite may be advantageously employed as a blackening process for reinforcing with bichloride of mercury ; this yields an opaqueness which is superior to that obtained from the ordinary development baths containing sulphite and is also superior to those which produce tarnishing by the use of ammonia.
For photographs on bromide paper the development, of pyrocatechine without sulphite yields very good images of a brownish tint, but when pyrocatechine without sulphite is used, there is no difference between the tint obtained by other developers.
This study of baths capable of producing a secondary image will be supplemented by further experiments, especially by sensitometric experiments ; for the moment we thought it wise to publish these first observations which may be of very special interest in many cases.
{from the Italian)
DEUTSGHER LICHTBILD DIENST
BERLIN, W. 35. G. m. b. H.
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