Great Facts / A Popular History and Description of the Most Remarkable Inventions During the Present Century

by Frederick C. Bakewell

"The woody fibres of leaves, and the wings of insects, may be pretty accurately copied; and in this case it is only necessary to cause the direct solar light to pass through them, and to receive the shadows on prepared leather. Images formed by means of the camera obscura have been found too faint to produce, in any moderate time, an effect on nitrate of silver. To copy those images was the first object of Mr. Wedgwood in his researches on this subject, and for this purpose he first used the nitrate of silver, which was mentioned to him by a friend as a substance very sensible to the influence of light; but all his numerous experiments, as to their primary end, proved unsuccessful."

It will be seen, from the foregoing account of the results of their experiments, that Mr. Wedgwood's process and the early processes of Mr. Talbot were nearly alike; and if he had possessed the means which the compound salt hyposulphite of soda afforded to subsequent photographers, of destroying the sensibility of the prepared paper to further impressions of the rays of light, there can be little doubt that the invention would have attained a high degree of perfection at the commencement of the present century. As it was, the failure of Mr. Wedgwood to accomplish the object he was so nearly attaining appears to have discouraged attempts by others, and twenty years elapsed without any advance having been made towards its realization.

M. Niepce, of Chalons on the Saone, who was the first to succeed in obtaining permanent representations of the images of the camera, commenced experimenting on the subject in 1814, at least ten years before M. Daguerre directed his attention to Photography. In 1826 these two gentlemen became acquainted, and conjointly prosecuted the investigations which led to the beautiful result of the Daguerreotype. M. Niepce having previously succeeded in obtaining durable representations of the pictures focused in the camera, he came to this country in 1827, and exhibited several of the results of his process, and communicated to the Royal Society an account of his experiments. These photographs, which may be considered the first durable ones that had been obtained, were, with one exception, taken on plates made of pewter. One of the largest was 5¼ inches long and 4 inches wide. It was taken from a print 2½ feet in length, representing the ruins of an abbey. When seen in a proper light, the impression appeared very distinct. Another one, which was stated to have been the first successful attempt, was a view taken from nature, representing a court-yard. Its size was 7½ inches by 6 inches, but it was not so distinct as the preceding one. A third specimen was an impression on paper, printed from a photograph on metal, the picture having been etched into the plate by nitric acid, and then printed from. All these specimens, though extremely curious as the first successful attempts to preserve the images of the camera, were more or less imperfect, and were far from presenting the beautiful results of Photography now attained. It is remarkable, however, that the original process of etching the picture on a metal plate, and printing from it, has now, in the perfected state of the art, become the most recent improvement; and the prints from photographic plates present some of the most beautiful effects hitherto produced.[2]

M. Niepce communicated the particulars of his process to M. Daguerre in December, 1829. They then entered into an agreement to pursue their investigations jointly, but it was not until ten years afterwards that the invention of the Daguerreotype by M. Daguerre was made known. To M. Niepce must, therefore, be awarded the honour of having first discovered the means of rendering permanent the transient images of the camera obscura. The plan he adopted was to cover a plate of white metal with asphalte varnish, and expose it to the action of light in a camera, when the parts whereon the light was concentrated became hardened, and the other parts remained unaltered, and could be washed away.

In M. Niepce's account of the process, after describing the preparation of the asphalte varnish, he says:—"A tablet of plated silver, or well-cleaned and warm glass, is to be highly polished, on which a thin coating of 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 on heated iron, which is wrapped round with several folds of paper, from which, by this method, all moisture has 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. The plate, thus prepared, may be immediately subjected to the action of the luminous fluid in the focus of the camera; but even after having been thus exposed a length of time sufficient for receiving the impressions of external objects, nothing is apparent to show that these impressions exist. The forms of the future picture remain still invisible. The next operation then is to disengage the shrouded image, and this is accomplished by a solvent."

The solvent employed was a mixture of one part of oil of lavender, and ten parts of oil of petroleum. The solvent was poured over the plate, and allowed to remain. M. Niepce continues: "The operator, observing it by reflected light, begins to perceive the images of the objects to which it has been exposed gradually unfolding their forms, though still veiled by the supernatant fluid, continually becoming darker from saturation with the varnish."

The time required for the exposure of the plates in the camera was six or eight hours. For the purpose of darkening the pictures, M. Niepce used iodine, and it has been supposed that the use of iodine for that purpose suggested the employment of it to his partner.

The process adopted by M. Daguerre was, to deposit a film of iodine on a highly polished silver plate, by exposing the plate to the vapour of iodine in a dark box. The prepared plate was then placed in the camera, and after an exposure of ten minutes or more, according to the brightness of the day, an impression was made on the iodised silver, but too faint to be visible. To bring out the image thus invisibly impressed, the plate was exposed to the vapour of mercury, in a closed box. The mercury adhered to the parts on which the light had acted, and left the other parts of the plate untouched; and by this means a beautiful representation was produced, in which the deposited mercury represented the lights of the picture, and the polished silver the shadows. The iodised silver remaining on the plate not acted on by light, was washed away by a solution of hyposulphite of soda, and the picture could then be exposed without injury.

Nothing can exceed the delicacy of delineation by such a Daguerreotype; for the fine surface of the highly polished silver seems to exhibit the impressions of the smallest objects that emit rays of light. The length of time required to produce an impression was, however, a serious obstacle to the use of the process, as originally invented, for taking portraits. Numerous attempts were consequently made to obtain a more sensitive material. Bromine was tried, in addition to iodine, and with such complete success, that a few seconds were sufficient to effect an impression on the plate, which could be forcibly brought out by the vapour of mercury.

It was in 1840 that portraits were first taken by the Daguerreotype process in this country. In the first instance, a concave mirror was employed to concentrate the rays of light on the plate, instead of a lens; and the author has now in his possession a portrait taken in this manner, by "Wolcott's reflecting apparatus." The object of using a concave mirror was to be able to concentrate a greater number of the rays of light than could be done by a lens, and thus to form a brighter image. At the time that portrait was taken, the means had not been discovered of making the mercury adhere to the plate, and a feather would brush it away. Soon afterwards, however, M. Fizeau ingeniously contrived to fix the images on the plate by gilding it. This was done by pouring on to the plate a few drops of a diluted solution of muriate of gold, and holding it horizontally over the flame of a spirit lamp; by which means the gold was deposited and formed a thin, beautiful film of the metal over the surface, and thus not only made the picture more durable, but gave it increased effect.