the white ground, it follows that the greater the proportion of color present in the film of a given thickness, the deeper will be the tint secured; and the less the amount of color present, the thicker must be the layer of the material in order to get depth. If, then, we take a sample of tissue prepared for a good negative, and print with a hard, dense negative, sufficient thickness of the colored translucent film is rendered insoluble to produce deep shadows and well-marked half-tones in the deepest gradations, long before the more delicate half-tones have been formed at all. If the printing be continued until these are secured, the lower half-tones forming the details in the shadows are obscured, sufficient thickness being rendered insoluble in the lighter of these shades to completely mask the underlying white ground. If with such a negative, however, we employ a tissue containing a much smaller proportion of color, it permits a considerable thickness to be rendered insoluble before the deeper half-tones are obscured; and in the time required for this, sufficient light has penetrated through the dense parts of the negative to render the details in the lights properly. On the other hand, by increasing the proportion of color, great contrast may be secured in the print, although little contrast may exist in the negative, as a slight thickness of the translucent material will, if it possess a large proportion of color, give great depth; and by the time the light has passed sufficiently through the thin deposit of a feeble negative to produce details in the lights, sufficient color will have been secured in the shadows to give vigor, without continuing the printing further, and so degrading the picture by rendering insoluble a further layer of color in the lights.
It will be seen, then, that by forming the picture in a thin film of insoluble matter of intense color, vigorous contrasts and perfect gradations from light to dark may
