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Negative Plate: To take these small portraits, Disderi first made a wet-plate negative plate with a special Camera that had four lenses and a plateholder that could be slid from side to side. Four exposures were made on each half of the plate; thus eight poses could be taken on one negative plate. A single print from this negative plate could then be cut up into eight separate portraits. Unskilled labor was used for this work; the production of the cameraman and printer was thus increased eightfold.
The dots appear in varying size, depending on the tones of the original photographs. A negative plate copy of the picture is first made with a camera, inside of which is fitted the halftone screen. This negative plate is then printed on a metal coated with bichromated gelatin. The dots on the negative plate allow light to penetrate and render the glue insoluble, so that when the plate is etched with acid each single dot remains on the surface of the plate, which is then mounted at type height on a wooden block. In the final print the minute clusters of dots cannot be distinguished, but appear as tones of gray.
At gross overexposure a negative plate will reverse to a positive. Direct exposure to the sun will often produce a transparent disc in the negative plate, which will appear in the print as menacingly black. Hence this reversal of tones is known as solarization. Because of this phenomenon the skies in wet-plate landscape negative plates were not uniformly black, but had patches of low density that gave a mottled appearance to the print. Consequently they were generally retouched around the contours with opaque paint and the remaining sky area was protected with a paper mask. |
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