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Herschel's Double Negatives

Herschel's Double Negatives

Two examples occur among Sir John Herschel's photographic experiments of 'doubled' photogenic drawings - two negative copies of the same engraving attached together (superimposed). The purpose is to use them in experiments with 're-transfer' or 're-reversal' (of the tones), as he called it at first - meaning positive printing, the techniques and viability of which were, along with fixing, the chief thrust of his experiments during 1839. Since silver-based photography (though not all photography) reversed the tones (see narrative to 34848), the invention's future depended on a straightforward method of 're-reversing' them that did not involve significant loss of clarity, detail, and contrast. Various expedients were tried - from manual ink retouching (see 42550) to waxing or varnishing (see 81920) to attaching sheets of mica (see 50435) - in the struggle to preserve and enhance detail and contrast (good clean light areas and good solid dark areas and lines) within the limited capabilities of the photogenic drawing at that primitive stage.

The double negative is one such expedient. Two nearly identical negative photogenic drawings on thin paper are superimposed in careful register. It increases the solidity (opaqueness) of the dark parts without (so long as they are clean hypo-fixed negatives) unduly compromising the light areas. One of the surviving pairs (87974) is attached by a small hinge of paper at the top right corner, and the top negative delicately retouched in areas carrying detailed highlights. Both negatives appear, perhaps deliberately, to be overexposed in the light areas. The other pair (27282) are stuck together by a translucent adhesive, probably canada balsam, and both coated with oil or varnish. The varnish, which darkens the dark areas and gives the rest an amber colour, makes it difficult to see whether they may also have been retouched. It also renders the paper extremely brittle, and the varnished double negative is consequently in poor and very fragile condition.

Other negatives surviving singly may of course have been used double or temporarily attached together. The only experimental positive certainly annotated as made from a double negative ('transfer from double-paper photog') is 97225, dated April 15-16, 1839. It is not made from either of the surviving double negatives, and is not significantly superior to straightforward positives.

Another reason given for making double negatives was that thin paper contained minute pinholes, causing spotting of any positive made from it, which was avoided in using two sheets where the pinhole defects would not coincide. For either reason the double negative could never realistically be more than a temporary experimental device, and illustrates, as with retouching, the painstaking lengths to which Herschel went to try every possibility in achieving his end. It was of course much better achieved by concentrating on the perfecting of the basic hypo-fixed negative (see narrative to 18871), and then in the longer term by the triumph of the latent image process and the glass negative. Although these were invented by others, Herschel anticipated both in his 1839 experiments, noticing a latent image phenomenon (43358 and 98244; and see narrative to 78062) and making the first successful photograph on glass (see 13193, reproduction).

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