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Herschel's Amphitypes (Mercurial Photographs)

Herschel's Amphitypes (Mercurial Photographs)

The specimens of 'Amphitype' and 'Mercurial Photographs' in packets 32 and 33 respectively of Sir John Herschel's photographic experiments are essentially the same process, and have a similar appearance. They were made on December 17, 18, and 19, 1842, and one in January 1843. The note (65918) indicates that they were exhibited, perhaps at the Royal Society, while the annotation on the wrapper of packet 32 (91242) indicates that those specimens, probably extracted from packet 33, were later exhibited or lent to someone, possibly at the 1844 meeting of the British Association for the Advancement of Science, by which time (as the note says) they were to Herschel 'very old impressions'.

Given the use of mercury in the daguerreotype (where it is not itself photo-sensitive but merely combines with the photo-sensitive silver), Herschel was interested to see if mercury salts had photographic capability of their own. He found that they produced photographic images which, under appropriate conditions, were of exceptional sharpness and attractiveness, but which either lost this quality on attempting to fix them, or faded continuously after fixing, even in the dark. The paper was prepared with ammonio-citrate of iron, as used for cyanotypes, and proto-nitrate of mercury. On exposure a negative image formed of a 'velvety brown'. It was fixed with bichromate of potash and long soaking in water; but although this arrested its darkening by light, Herschel found no way of preventing its fading over time.

Once faded, however, he found that the 'dormant' image could be restored by soaking in a weak solution of pernitrate of mercury, and then washing and ironing with a warm iron (so Herschel claimed). Surprisingly the image thus restored was a positive in black tones, not the brown negative it had started as. It was (in spite of common assumptions) one of the few literally black and white processes achieved in all the vast range of early photographic experiments. Because the strong black resembled printer's ink, the results in copying engravings were particularly striking, looking as if one of the aims of Herschel and his fellow experimenters, to develop photography as a print-making technique, might be achieved. However, there was no way to fix the image either against darkening or against fading. This dual process (the negative fading and then being restored as a positive) was actually what Herschel intended the term 'amphitype' to apply to, and the 'Black Specimen' mentioned on the note (65918) was an example of it.

Presumably because of their propensity to fade, Herschel has packaged his 'Mercurial Photographs' in two protective wrappers (11886 and 30634), one within the other, both made of paper with a black coating on one side -- the only example of such in the collection. The ageing test for instance (94276) is contained in a wrapper of thick brown paper. The aim may be partly to minimise the photographs' deterioration by affording them complete protection against light; more consistent with Herschel's experimental approach, its purpose is to afford them complete protection against light in order to validate his conclusion, that they fade anyway.

It has been assumed, and lamented, by Schultze and other scholars who have studied the Oxford collection, that the black specimen is not present. However, given Herschel's conclusion that the black image could not be preserved and would fade over time even in its protective packet, and his implication (in his published remarks) that the exposed mercury papers fade back to the yellowish colour of the pre-exposed paper, it might rather be the case that one of the surviving examples is in fact the formerly black specimen. The three photographs presently in packet 33 are all negatives (though without discernible images), two of them yellow; while both of those in packet 32, assumed to have been extracted by Herschel from packet 33, are positives, with very faint surviving images, one yellowy and the other pale sepia. The former is dated both December 18 and 19, and so is definitely a companion to those in packet 33, but unlike them has been subjected to two procedures; the other was made in January 1843, and has several annotations including the word amphitype and 'Brought out Jan 15/43' (Herschel's term for developing or reviving a latent image). Both of these were thus originally true amphitypes -- the negative revived as a black positive -- and one of them was thus presumably the original 'Black Specimen' in packet 33. They were already faded by the time of Herschel's second note (91242, on the wrapper of packet 32): 'both much faded very old impressions'.

The word amphitype was suggested to Herschel by Talbot. The Greek amphi- means both ways, though it can also mean ambiguous. It became ambiguous, as a term, since Talbot used it again later for an entirely different process, and it was also the original name for the collodion positive (ambrotype). By this time it was apparent that nothing would come of Herschel's mercury processes, promising and scientifically interesting as they were. It is tempting to think that even his original term for these 'Mercurial Photographs' was used playfully, in view of their fickleness, since of course the word 'mercurial' in common parlance means fickle or volatile.

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