The chemical processes used by John and Robert Adamson and the possibility that they might have used some special ingredient has long been the subject of speculation. In the early stages of photography in Scotland, the chemical processes used were probably based on William Henry Fox Talbot's, but it is likely that independent experimentation followed rapidly. Visual differences among the images produced by John Adamson and, to a lesser extent, David Octavius Hill and Robert Adamson, support the use of several different processes. In a few instances, annotations in the original albums or on the negatives provide tantalizing clues to the chemistry used, but these are scarce and there are no known notebooks left by either John or Robert Adamson to reveal their photographic recipes. They did, however, leave a vast corpus of images, which may be able to shed light on the chemical processes employed. This requires non-destructive analytical methods for determining the elements now present in the image and relating these to the chemicals employed originally.
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