THE power possessed by solar light, and in a less degree by artificial light, in producing chemical change in the various organic and metallic compounds of the earth has been long known, and excited the attention of the most able chemists and philosophers of the day.

For several centuries the darkening effect of the solar rays on chloride of silver has been remarked. More recently, Sir Humphrey Davy and Mr. Wedgwood turned their attention to this curious subject, and endeavoured, but without success, to apply it to useful purposes. They were stopped at the very commencement of their inquiries, by the want of a fixing agent, to prevent any further change taking place on the prepared surface employed, after the required effect had been produced. They were unable to overcome this difficulty, and consequently abandoned the pursuit.

Although the progress of the inquiry was checked by this difficulty, it was not entirely abandoned; for, after much labour and patient investigation, means were found to prevent the action of light beyond the desired point. Without this power, the entire labour would be thrown away, for the impression received would quickly disappear in the general darkening of the whole surface.

From these small beginnings, a new Art has been discovered, beautiful in its results, commanding equally the attention of the artist and the man of science. The chemical philosopher will find in it a new study, and wide field of research open to his view; presenting, in fact, an entirely new branch of chemical inquiry; and he cannot fail to be struck with the great power which a very feeble ray of solar light possesses, in producing a rapid chemical change in some bodies when presented to its influence, the consideration of which may induce him to devote some portion of his time to the investigation of a subject, so interesting in its details and marvellous in its effect. He will also observe how very large a portion of the solar rays, though not absolutely necessary to illuminate and brighten the face of the natural world, are not less essential to our well-being, and are silently working with powerful effect in producing remarkable changes, and modifying by their influence the most enduring, as well as the most fragile, of nature's productions.

The artist will avail himself of Photography for noting down the aspect and changes which are constantly varying the face of nature, opening to his observation many striking effects of light and shadow, which, without its aid, would altogether escape his observation, or elude the vigilance of his pencil to note down. To him it will prove a valuable assistant in abridging the labour in collecting sketches of various objects of interest, the minute details of which he , hut which would encroach too much on his time and patience, if obliged to have recourse to his pencil to delineate them.

Although the great precision and minuteness of detail of the impression produced on the prepared plate would go far beyond his ideas of what is absolutely required of him to be produced with his pencil, still he has the power, when assisted by a proper judgment, of omitting in his finished productions such details as are not necessary to produce the effect he desires.

It must not be imagined that photography can ever take the place of the painter's art in its higher branches, as more likely to give faithful portraiture and correct ideas of character and expression.

In Portraiture, for instance, the artist will seek for a certain and well-known expression characteristic of his sitter, without which, he well knows, that his picture, although conveying every other detail with correctness, would be a failure. On the other hand, what photographer has not observed how the various impressions he has taken of the same features, perhaps in succession, vary considerably, without any of them representing fully the characteristic expression of the sitter? In this point of view, it will be seen, that photography is widely separated from art, and cannot easily accomplish all that is required at the hands of the artist.

The process with Collodion was originally given by me in the March number of "The Chemist", 1851; and I had in a previous communication to the same journal made known the great power of pyrogallic acid as a developing agent.

Since their introduction, photography has made most rapid strides towards perfection, various improvements have been suggested in its manipulation, all tending towards the ultimate perfection of the process; and it will be my aim in the present Manual to describe such improvements as I consider essential, and worthy to be adopted by the photographer.

It will be as well to say a few words in reference to the various experiments which led me to adopt collodion as a medium, so well adapted for receiving the chemical agents necessary in this beautiful art.

In my first account of the Collodion Process, I alluded to the difficulties attending the use of paper, and described them as being too great ever to be overcome, on account of the unevenness of its texture and other defects.

My first attempts with collodion were directed to the improvement of the surface of paper, by spreading over one side a thick solution of collodion.

These essays were not successful, for, after the necessary washing, &c., in the process, the collodion film did not adhere to the paper sufficiently to be of any use.

However, previous to and during the progress of these experiments, I was trying various other substances as media, for holding the chemical agents zyloidin, other modifications of starch, extremely fine paper pulp, tanno gelatine solutions, and several combinations of albumen. Each had its turn, and it was only after innumerable experiments in various ways that I decided on collodion as being the best, and, at the same time, the most available substitute for paper. Its exceeding ease of manipulation, and the brilliancy of the pictures obtained with it, cannot fail to strike every one who sees them; and justifies me in the opinion I entertain of its value and practical importance.

With regard to the introduction of collodion as the foundation of the process, I must say a few words.

Collodion, there is no doubt, early attracted the attention of photographers, but who first actually suggested its use, we have no means of determining with any precision; since however its value as a photographic agent has been known and appreciated, many claimants have come forward anxious to obtain a share in the merit of its first introduction.

There can be little doubt that many of those engaged in the the pursuit of photography, anxious to improve the then known processes or invent others, would very soon have collodion brought under their notice, proceed to test its capabilities as a photographic agent, and possibly endeavour to work out a process by which it could be made available in the art.

It is indeed obvious, from a consideration of its remarkable qualities, that it could not long escape their observation, and we may easily imagine also that it would be likely to attract simultaneously the attention of many parties who were labouring in the same field of research.

It is evident that, in deciding a question of this kind, the first published account must take precedence of any other kind of proof, and it is due to M. Gustavus le Gray, a gentleman whose great services in other branches of the art of photography are well known, and are held in high regard, to say that he was the first to publish an account of collodion as a photographic agent. I allude to his pamphlet published in 1850, wherein he mentions collodion and its possible use.

His first application of it appears to have been as an encollage for paper. Afterwards he used it on glass, and gave in his memoir a short account of his researches, but no manipulation in as made known, such as would entitle it to be called a photographic process; and from the wording of his published notice, it would appear to have been merely an extract from his note book of chemical experiments; as such it attracted little attention at the time; still M. le Gray must be considered the first party who, by publication, made known his researches on the subject, and although this notice did not lead to its practical use, it establishes his claim to be considered the first to suggest its value in photography.

About the month of June, 1849, I began to turn my attention to collodion as a substitute for paper, with the hope that by its means a surer and more delicate medium might be produced to work upon than paper was ever likely to be.

I tried numberless experiments with it, and varied the mode of using collodion, with the hope of getting at a practicable and sure method of working it.

These experiments were carried on until the month of March, 1851, when I published in "The Chemist" a short account of my experience in the matter; giving a process in detail, the mode of preparing collodion with iodide of potassium and silver, the proper strength of the nitrate of silver bath, the best proportion of pyrogallic acid for developing the latent picture, with the manner of fixing the picture produced; in fact, giving the whole of the process in detail.

It will therefore be evident, that although M. le Gray has the merit of having been the first to make known this valuable photographic agent, still as he did not, at the time of his publication, produce it as a process with the necessary details to make it intelligible to the photographer, his claim must in consequence be limited, and cannot in justice interfere with the merit of another party, who, from his own experience, made known a process with collodion, and that without any assistance from, or reference to, the labours of others in the same field of research.



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