A Manual Of Photography

@@8665 CHAPTER II. HELIOGRAPHY- THE PROCESS OF M. NIEPCE. M. Niepce was tlie first inquirer who appears to have produced permanent pictures by the influence of the sun's rays. This process—Heliography—is in many respects peculiar, which renders it necessary, although his preparation was only acted on by an exposure of many hours to full sunshine, to give a parti- cular account of it; the more so, as some points of considerable interest require further elucidation. , The substance employed by M. Niepce was asphaltum, or bitumen of Judea. He thus directs its preparation:—“ I about half fill a wine-glass with this pulverised bitumen; I pour upon it, drop by drop, the essential oil of lavender,1 until the bitumen is completely saturated. I afterwards add as much more of the essential oil as causes the whole to stand about three lines above the mixture, which is then covered and submitted to a gentle heat until the essential oil is fully impregnated with the colouring matter of the bitumen. If this varnish is not of the required consistency, it is to be allowed to evaporate slowly, without heat, in a shallow dish, care being taken to protect it from moisture, by which it is injured, and at last decomposed. Tn winter, or during rainy weather, the precaution is doubly neces- sary. A tablet of plated silver, or well cleaned and warm glass, is to be highly polished, on which a thin coating of the varnish is to be applied cold, with a light roll of very soft skin: this will impart to it a fine vermilion colour, and cover it with a very thin and equal coating. The plate is then placed upon heated iron, which is wrapped round with several folds of paper, from which by tins method all moisture had been previously expelled. When the varnish has ceased to simmer, the plate is withdrawn from the heat, and le ft to cool and dry in a gentle temperature, and protected from a damp atmosphere. In this part of the operation a light disc of metal, with a handle in the centre, 1The English oil of lavender is too expensive for this purpose. An article sold as the French oil of lavender, redrawn, is very much cheaper and answers in every respect as well, if not better.