A Manual Of Photography

256 PRACTICE OF PHOTOGRAPHY. plates. The required surface is thus produced with one-third the labour, and a very great saving of time ; besides which, the silver is in a much more susceptible state for receiving the vapour ot the iodine. The plate being thus prepared, we proceed in the manner before directed., It is somewhat singular, that on the first notice of Daguerres pictures. long before the publication of his process, when 1 fearnt that they were on ‘1 hard polished tablets,” I entertamed the idea that'plates of copper thus silvered were oxidised, and then acted on by iodine. I applied the iodine both in solution and vapour; but, of course, as the mercury was not used, I failed to effect any perfect pictures. It is, however, worthy of remark, that on one occasion, having placed a piece of silvered copper in a trough containing a weak solution of iodine, with some leaves of hemlock superimposed, these being kept close by means of a piece of glass, over all the exposed portions the silver was completely removed, and the copper abraded to a considerable extent while beneath the leaves the silver was scarcely affected. I thus procured a very beautiful etching, the figures benig in hi^h relief. This was frequently repeated with success ; but other inquiries having drawn off my attention, the process has been long neglected, although I am convinced it is capable of being turned to much useful account. ., In November 1839, I pursued a series of experiments with bromine but no very definite advantage was obtained. Some curious effects which I noticed at that time are worthy of notice. I copy the remarks made in my memorandum-book at the time. 41 Exposed a plate to the vapour of bromine: it assumed a leaden-grey colour, which blackened by light very readily. Ex- posed this to mercury without much improving the effect or altering the lights. Upon immersing this plate in a solution of the muriate of soda, the parts unacted on by light became a jet black, whilst the parts on which light had acted were dissolved off leaving a clean coating of silver. The effect was most decisive—« black picture on a white ground. 8 Allowed three plates to assume—the first a straw-yellow, the second a steel-blue, and the third a dull blue, and examined their sensitiveness ; the plate which had arrived at the dull blue colour appeared to be the most sensitive.. These experiments, which were then pursued with a view to produce more permanent pictures—to fix the mercury, or o engrave the plate-were, however, abandoned, and have not yet been resumed, although it is desirable that some one should turn his attention to this point. On one occasion, after having prepared a picture according to the process prescri e )