The following excerpt comes from A Manual of Photography by Robert Hunt. This 1854 version is the fourth edition of the book – amazing when you consider that photography was still a very young technology. Hunt goes into its history for us, beginning with Niepce, who is stilled credited as the first photographer.
Heliography: The Process of M. Niepce
M. NIEPCE was the 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 particular 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 lavender1, 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. In winter, or during rainy weather, the precaution is doubly necessary. 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 this method all moisture had been previously expelled.
When the varnish has ceased to simmer, the plate is withdrawn from the heat, and left to cool and dry in a gentle temperature, and protected from a damp atmosphere. In this part of the
operation a light disk of metal, with a handle in the centre, should be held before the mouth, in order to condense the moistureof the breath."
The plate thus prepared is now in a fit state for use, and may be immediately fixed in the correct focus of the camera. After it has been exposed a sufficient length of time for receiving the
impression, a very faint outline alone is visible. The next operation is to bring out the hidden picture, which is accomplished by a solvent.
This solvent must be carefully adapted to the purposes for which it is designed: it is difficult to fix with certainty the proportions of its components, but in all cases it is better that it be too weak than too strong; in the former case the image does not come out strongly; in the latter it is completely destroyed. The solution is prepared of one part – not by weight, but volume – of the essential oil of lavender, poured upon ten parts, by measure also, of oil of white petroleum. The mixture which is first milky, becomes clear in two or three days. This compound will act until it becomes saturated with the asphaltum, which state is readily distinguished by an opaque appearance, and dark brown colour. A tin vessel somewhat larger than the photographic tablet, and one inch deep, must be provided. This is to have as much of the solvent in it as will cover the plate. The tablet is plunged into the solution, and the operator, observing it by reflected light, begins to see the images of the objects to which it has been exposed slowly unfolding their forms, though still veiled by the gradually darkening supernatant fluid. The plate is then lifted out, and held in a vertical position, till as much as possible of the solvent has been allowed to drop away. When the dropping has ceased, we proceed to the last, and not the least important operation, of washing the plate.
This is performed by carefully placing the tablet upon a board, B, fixed at a large angle, in the trough a a, the supports being joined to it by hinges, to admit of the necessary changes of inclination, under different circumstances: two small blocks, not thicker than the tablet,
are fixed on the board, on which the plate rests. "Water must now be slowly poured upon the upper part of the board, and allowed to flow evenly over the surface of the picture. The descending stream clears away all the solvent that may yet adhere to the varnish. The plate is now to be dried with great care by a gentle evaporation: to preseire the picture, it is requisite to cover it up from the action of light, and protect it from humidity.
Editor's Note: – It's kind of amazing to read about pioneer process-makers. Just think: if you didn't know how to do this, could you have come up with it? We are also impressed with the patience and care it took to prepare the plates and develop the pictures. That's dedication. The next time somebody drones on and on at you about the latest in digital cameras – yeah, I know, I want a Light L16, too, but I don't have $1300 lying around – and beats your ear about f-stops and the like, just think of Niepce and smile knowingly.