A Manual Of Photography

ON THE APPLICATION OE THE DAGUERREOTYPE TO PAPER. 91 Section VIII.—On the Application of the Daguerreotype TO Paper. The expense and inconvenience of metallic tablets rendered it in the highest degree desirable that paper should he employed in their place. A very extensive series of experiments at length led to the pleasing conclusion of being enabled to prepare a paper which answered in every respect as well as the silver plates, and in many much better., This discovery formed the subject of a communication to the Royal Society, which that learned body did me the honour to print in their Transactions. My memoir is entitled,—“ On the Influence of Iodine in rendering several Argentine Compounds, spread on Paper, sensitive to Light ; and on a New Method of Pro- ducing, with greater distinctness, the Photographic Image. 1 is paper contains the substance of the following remarks ; but since the publication of the Transactions I have been successful in simplifying the process of preparation. My experiments established, in the most satisfactory manner, that even on the silver tablets a semi-oxidized surface was pre- sented to the iodine. They also proved that perfectly pure untarnished silver was by no means readily acted on by the iodine. From this I was led to prepare oxides of silver in many different ways, which enabled me to spread them over paper, and the result was instructive. Any of the ordinary photo- graphie papers allowed to darken to a full brown, which is a stage of induced oxidation, become, by long exposure to iodine, of a steel-blue or violet colour. If exposed in this state to sunshine for a long period, their colour changes from grey to a clear olive. Now, exposure to sunshine for a minute, or to dif- fused daylight for five minutes, produces no apparent change; but mercurial vapour speedily attacks the portions which haae been exposed to light, and a faithful picture is given of whatever may have been superposed. There is, however, a want of suffi- cient contrast between the lights and shadows. By allowing the first darkening to proceed until the paper acquires the olive colour which indicates the formation of a true oxide of silver, it will be found, although it is not more speedily acted on by the iodine, that it is more sensitive, and that a better picture is formed. The kind of photographic preparations used appears to have but little influence on the results,—a chloride, iodide, or bromide of silver, allowed to darken, answers equally well. There are many things, unfortunately, which prevent our