REPORT OF MR. W. J. STILLMAN.
363
effected by allowing the granular substance to depose gradually in the fluid gelatine, so that, when the film has been exposed, the induration caused by light penetrates to the coarser deposit, which elsewhere is washed away, leaving the coarseness of grain in the result proportional to the depth of induration, i. e., to the transparency of the negative; and, as this is in the shadows, of course the photo-engraving plate produced by electro-deposit, will have the desired granulation more strongly marked as the shadows are deeper.
The results of this process, in the hands of a French firm who are working it commercially, rival in effect and far surpass in fidelity the best mezzotint engraving.
The chromatized gelatine, charged with such color as may be desired, becomes also the basis of a light-printing process, long known as the Autotype, in which a tissue prepared for the purpose is exposed to the action of light under the negative ; and then, being immersed in tepid water, the unindurated gelatine is washed away, carrying the color with it and leaving the protected parts of the tissue thin and colorless in proportion to their degree of protection.
Any tint or pigment may be employed. This process, however, from the fact of its continual dependence on light, each impression being produced from the negative as in the chloride of silver process of printing, can hardly be expected to maintain a permanent footing beside the mechanical processes. The Autotype Company, however, have developed another admirable use for this gelatine tissue, by preparing it with a strong color and then supporting it by glass instead °f paper, so that, on development, it makes a transparency with all the exquisite delicacy of detail and gradation which have been alluded to as belonging to the gelatine film. From this, by an enlarging camera, a new negative is made of any required dimensions, preferably not to exceed eight diameters of the original negative, the enlarged prints thus produced having a charm quite unique; and if the original negative was well calculated for the purpose, with no loss of an y of the qualities most desirable in a photograph. By this a Pplication of the various facilities drawn from the optical, chemical and mechanical resources of photography, the small- est apparatus which it is desirable to use may be made to