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Herschel's Oak Leaf

Herschel's Oak Leaf

Sir John Herschel's photographic experiments began on January 29, 1839, and in their first phase aimed chiefly at establishing a chemistry and procedure for fixing the image and cleaning its highlights. He concentrated on sodium thiosulphate (which he called hyposulphite of soda, and later photographers called hypo), and this photograph is one of the best of the concentrated series of dated hypo fixing experiments he conducted during February 1839, establishing the validity of the process. Specimens of June to October 1839 (for example 18871, 23691, 32610) show it in fully perfected form.

February 26 was a busy day. Thirteen of the surviving, dated experiments bear that date, though varying from complete failures (such as 36945 and 85108) to surprisingly excellent images (this and 16969). Both hypo and potassium ferrocyanide (33623, 36945, 78723, 87956, 97903) were being tried as fixatives on that day, but although interesting effects were sometimes achieved with the latter (see 18583, 60166), hypo consistently and from the outset did the job better than any of the alternatives.

The chemical basis of the image is the conventional photogenic drawing process as published by Talbot, washing the paper in sodium chloride (common salt solution) and brushing it with a light-sensitive silver salt (usually nitrate, though chloride and carbonate were also effective). It has then been exposed in sunlight in contact with the leaf, held together between sheets of glass, for as long as it took for an image to appear.

Herschel's experiments came to the Museum of the History of Science in 1928, presented by his two surviving and youngest daughters, Miss Francisca Herschel and Lady Constance Lubbock. The oak leaf was one of the specimens displayed in the Museum from about that time until the 1980s. Because it was removed from context at so early a date, its original place in the sequence of Herschel's original packets is not known; February 26 experiments occur in at least four of the packets. Being so distinctive, and being singled out for display, the oak leaf became one of the best known of Herschel's experimental photogenic drawings, being reproduced in several publications from the 1930s onwards. But ironically it is omitted from Schultze's 1965 article (the standard description of the collection) because he failed to notice it was on display in the Museum.

Herschel's experimental photogenic drawings are experiments in photographic chemistry, not pictorial images, nearly all of them being made by copying engravings. Other experimenters such as Talbot and Hunt made more use of leaves and plants (see for instance 49660 and 38110), so it is natural that Herschel should try it. But surprisingly this is one of only three contact-copies of actual objects, and the only leaf, among Herschel's experiments (the other two being pieces of lace, 26027 and 30855). The reason is that the engravings provided a stable and repeatable experimental comparison and control, without which he would not have regarded his work as serious experimental chemistry. He also shared the common assumption at the beginning of photography that its chief usefulness would be as a means of duplicating engraved and other prints.

The particular circumstances that led him to use this oak leaf on February 26, and the significance of the added letter, are not known. The letter is a reversed T (it has usually been read as a J, but comparison with Herschel's handwriting proves it to be a T). It has been written or painted on the leaf itself, and is laterally reversed as were all negative images. Perhaps it was meant to be Talbot's initial, or perhaps someone with that initial was visiting Herschel that day and participating in the experiment (compare the experiment in invisible writing 78062, which contains the names of four of Herschel's children).

The image in 2010 is clear and probably stable, but has faded due to being displayed in the museum for so many years. A black-and-white photograph of it taken in 1933 shows a stronger and more contrasty image.

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