About 1825 Dagnerre became acquainted with the fact that Niepce had been working in the same direc tion, and with apparently far greater success than him self. The two formed a partnership, and working together invented the process known as Daguerreotype. Before its publication Niepce had died, and Daguerre purchased from his son the right to omit any mention of him in connection with the publication of the process which bears to this day the name of Daguerreotype.
The year 1839 was a momentous one in the history of photography. Daguerre in France published his process, which at once gained popularity ; and almost simultane ously Fox Talbot in England published his method of photographic drawing on paper, which must be con sidered as containing the germ of the negative processes of to-day.
And now there occurred what we almost always see when a great discovery is made, what we have so recently seen in connection with electric light, the tele phone, microphone, and phonograph. The public, at first indifferent, passed over to the opposite extreme. The most wildly-extravagant expectations of what the new process was to do were entertained. Painters were shortly to be no more required. A small step only in advance seemed necessary to secure the rendering of natural colours. The most impossible things were to be done. From this there was naturally a reaction. The Daguerreotype had so far obtained the larger share of public favour. The appearance of a picture by this process may not be known to all. The medium is a plate of polished silver, somewhat like a mirror, and on the surface is a picture beautifully delicate, but neither very bold nor distinct, requiring to be looked at from a certain angle. Daguerreotypes are not in all respects pleasing representations at the best, and it will readily be understood that the crudities which occur too often, even in the present clay, in photographs, from want of artistic knowledge and taste, were much more conspicu ous at a time when few were trained to the process, and when exposures were such as would now be considered extravagantly long.
The Daguerreotype fell into comparative disrepute, and the process of Talbot•, which as improved in 1841 by its originator was of far greater general utility than that of Daguerre, advanced in favoni- but slowly.
It was not till Archer in 1850 invented the process known as "wet-collodion," and which up till within a couple of years ago was the popular process with both amateurs and professionals, that photography began to assume the importance which has been attached to it in late years.
A few words must be said in description of the manipulations used in the processes which we have mentioned.
That of Daguerre is the first which requires descrip tion, those before having never passed the experimental stage.
In this a silver surface is required. For economy a copper plate is used, which is thickly plated with silver. The silver surface is polished and most carefully- cleaned. Afterwards it is exposed to the fumes of iodine. A thin film of iodide of silver is thus produced, and this is sen sitive to light. The sensitiveness is, however, slight as compared with the films which we use in the present clay. An exposure of several hours was generally required.
A great improvement was made by employing the vapour of bromine combined with the iodine. The ex
posure was thereby reduced. The greatest improvement in the process was, however, the discovery of decelop men t.
Development is a process which requires some ex planation, as it is the point on which turns the success of every modern process of photography.
A tale is told of the discovery of development by Daguen.e. It is as ill authenticated as the others which are told of him, but may, nevertheless, be recounted, as it will serve better to give an idea of the operation than a long description would.
It is told that Daguerre, during his experiments, had inadvertently given to several plates so short ex posures that little or no image was perceptible. These he placed on one side in a cupboard, with the intention of repolishing them at his leisure, and of using them again.
His surprise may be imagined when, on returning after the lapse of some time to his cupboard, he found that each plate had on it a picture apparently perfectly exposed. His first idea was that his cupboard was be witched, his second that possibly some of the chemicals which were stored beside the plates affected them. He proceeded to place on the shelf where the first plates had been other under-exposed ones, removing after each was placed there one of the chemicals. Still, however, the apparently magical process went on. At last he bethought him of some mercury which had been spilt on the wood. This was indeed the magic substance. Further investigation showed him that a portion of the iodide of silver film, exposed to light for a period too brief to cause on it a visible change, yet had acquired a selective power and attracted to itself minute globules of this vapour of mercury, thus becoming visible. After wards the process of " development," as it was called, was regularly carried out by placing the plates, bearing apparently no image, over a vessel containing mercury, which was heated. This process of development should be well borne in mind. Something of the same kind— that is to say, a strengthening by some means of an image so weak as to be generally at first invisible, till it becomes as strong as we desire—takes place in every photographic process.
The chief difference between the process of Daguerre and Talbot lay in this, that whereas the Daguerreotype is a positive process, the Talbotype is a negative one. The result of exposing a Daguerreotype plate was one finished picture with the lights and shades correct, but, unless a mirror or prism reflector was used, with right and left transposed. If a second copy were required, the whole operation had to be gone through again.
A Talbotype represented the shades of nature reversed. The darker shades are represented as white, the lighter shades as black. From such a negative it was, however, possible to get any desired number of copies with the shades correct, and without transposition of right and left.
Talbot used paper as a support for his sensitive salt, which, as in Daguerreotype, was iodide of silver. His negatives were developed with a solution of gallic acid, and afterwards the paper was rendered as transparent as possible by the application of white wax so as to faci litate the taking of copies, or " printing," as it is usually termed.