Photography On Paper And On Glass
( Originally Published 1898 )
WHILE Niepce and Daguerre were perfecting their process, another investigator was working on similar lines, and arrived at like results by a different method. This was Henry Fox-Talbot, who is entitled to rank with the two Frenchmen as an independent discoverer in photography. Fox-Talbot was born at Laycock Abbey, Wilts, in the first year of the century, and was educated at Harrow and Trinity College, Cambridge, where he carried off the Porson prize for Greek verse in 1820, and graduated as twelfth wrangler in the following year. He sat in the first reformed Parliament for Chippenham; but, scientific investigations being more to his taste, he gave up politics after two years, and devoted himself to studies that led to a discovery which proved one of the first steps towards the realisation of photography.
Fox-Talbot tells us in his " Pencil of Nature," published in parts between 1844 and 1846, how, in attempting to make a drawing, by means of the camera obscura, of a landscape on the shores of Lake Como, his thoughts were turned by the imperfect attempts he made to copy the pictures of surrounding objects presented by the apparatus to the possibility of fixing by some chemical process those exquisite shadows. To the realisation of this idea he devoted himself with the utmost zeal and perseverance, and gradually arrived at a result that was as surprising to him as it was satisfactory.
He began his experiments in 1833, and his first method consisted, as described in the Philosophical Magazine, in soaking fine writing paper in a weak solution of common salt, then brushing one side of it with a 12 per cent solution of nitrate of silver in water, and drying it at the fire. By repeating the process of saturating the paper with salt solution, and then coating it with the nitrate of silver, greater sensitiveness to light was produced. This increased sensitiveness was due to the use in combination of the two salts of silver, the nitrate being in excess.
Fox-Talbot states that by means of this paper, he was enabled to obtain in the solar microscope an outline of the object to be depicted in full sunshine in half a second; while, after an exposure of about an hour, he had the gratification of receiving an impression of the image cast by the lens upon the white paper in the camera obscura. To this point in his discoveries he had attained in 1835.
Thus far Talbot's process was the same as that by which Wedgwood and Davy had obtained their results more than thirty years before; only he had succeeded in rendering chloride of silver much more sensitive to light than they were able to do. The problem, therefore, which had baffled those investigators yielded to the perseverance of Fox-Talbot. He found that by thoroughly washing his impressions, and then soaking them in a solution of common salt, or in a solution of potassium iodide or bromide, he turned them into permanent pictures. In short, he had discovered the secret of "fixing."
For six years Fox-Talbot kept the secret of his investigations to himself, and was only then impelled to divulge his process by hearing that a Frenchman had succeeded in fixing the silhouette of the camera obscura. On the 25th of January 1839, Professor Faraday described Fox-Talbot's method of " Photogenic Drawing," as the inventor called it, to the members of the Royal Institution ; and a few days later the inventor himself read a paper before the Royal Society giving a full account of his process.
In this paper he says: " The first kind of objects which I attempted to copy by this process were flowers and leaves, either fresh or selected from my herbarium. These it renders with the utmost truth and fidelity, exhibiting even the venation of the leaves, the minute hairs that clothe the plant, etc., etc."
He proceeds: " At the very commencement of my experiments upon the subject, when I saw how beautiful were the images which were thus produced by the action of light, I regretted the more that they were destined to have such a brief .existence, and I resolved to attempt to find out, if possible, some method of preventing this, or retarding it as much as possible. The following considerations led me to conceive the possibility of discovering a preservative process.
" The nitrate of silver, which has become black by the action of light, is no longer the same chemical substance that it was before. Consequently, if a picture produced by solar light is subjected afterwards to any chemical process, the white and dark parts of it will be differently acted upon; and there is no evidence that after this action has taken place, these white and dark parts will any longer be subject to a spontaneous change; or, if they are so, still it does not follow that that change will now tend to assimilate them to each other. In case of their remaining dissimilar, the picture will remain visible, and therefore our object will be accomplished."
Applying this process of reasoning, Fox-Talbot, after some unsuccessful trials, " discovered a method which answered perfectly, and shortly afterwards another." After commenting on the marvellousness of the process by which " a shadow, the proverbial emblem of all that is fleeting and momentary, may be fettered," he has the following reflection on the value of scientific method. " This remarkable phenomenon," he says, "of whatever value it may turn out in its application to the arts, will at least be accepted as a new proof of the value of the inductive methods of modern science, which by noticing the occurrence of unusual circumstances (which accident perhaps first manifests in some small degree), and by following them up. with experiments, and varying the conditions of these until the true law of nature which they express is apprehended, conducts us at length to consequences altogether unexpected, remote from usual experience, and contrary to almost universal belief. Such is the fact, that we may receive on paper the fleeting shadow, arrest it there, and in the space of a single minute fix it so firmly as to be no more capable of change, even if thrown back into the sunbeam from which it derived its origin."
With this first success, however, Fox-Talbot did not rest satisfied. After seeing a description of Daguerre's process, he made some experiments with silver iodide in place of chloride, the process to which he gave the name of " Calotype " being the outcome. Paper already sensitive was brushed over with a mixture of silver nitrate and gallic acid, and then, in a half-wet state, exposed in the camera. By this method the time necessary to secure a picture was greatly reduced. Development was effected by an application of gallo-nitrate of silver, exposing the picture at the same time to a gentle heat.
In lighting upon gallic acid as a developer, Fox-Talbot showed a remarkable application of the induction process of reasoning. Daguerre had found that if his prepared plates were exposed to the light, even only for a few seconds, a picture could be obtained by afterwards exposing them to the action of mercurial vapour. As Talbot used for the preparation of his paper the same material Daguerre had on his plates, he concluded that the exposure of the paper for a few seconds to the action of light in the camera obscura must have produced an impression. Talbot was convinced therefore that there must be a picture on the paper, although he could not see the least trace of one. This conviction spurred him on to search for something that would make the latent image visible, for he had no doubt such a thing was really to be found.
How came he then to employ for this purpose a solution of gallic acid ?
The solution of this problem most persons might be inclined to attribute to chance, as was the case with Daguerre's pictures. Talbot's selection of gallic acid, however, was no haphazard affair. Daguerre had not placed the vessel of mercury in the cupboard in prosecution of his experiments. His pictures were obtained without his doing anything for this purpose. Talbot, on the contrary, racked his brains in the search after a means suited to his particular object. He had before his mind's eye many thousands of substances from which to choose, but his analytical faculty instinctively excluded from his survey all those that stood in no relation to his purpose, and directed him to those which acted in a similar manner when under the influence of light.
The salts of silver are blackened by gallic acid when slightly heated, as well as by light; the action of both is identical in kind, although gallic acid is much the more powerful of the two. The solar rays had, as he conceived, produced an action upon the prepared paper in the camera obscura, albeit so slight that it was not visible; perhaps—so he reasoned—this action might be carried on and augmented by means of gallic acid. Acting upon his thought, he tried the experiment. It was entirely successful, and the justness of the induction was thereby proved.
The "fixing" was done by washing in pure water, and, after drying, treating the paper with a solution of bromide of potassium, and again washing and drying. The paper "negative," as it was called, was now rendered translucent with wax, and used for the production of positive prints.
This was effected by placing beneath the negative a piece of sensitized paper and then exposing it to the action of light. By this means a second impression was obtained, the image being in this case, so far as light and shade were concerned, the exact reverse of the first one. Talbot appears to have been the first to conceive the idea of thus making use of the negative for the purpose of getting a direct image, and hence may be said to have been the originator of photographic printing.
It should be said that the method of developing by means of gallic acid and nitrate of silver appears to have been first known and applied by the Rev. J. B. Reade, who, when taking objects in the solar microscope, employed those agents to render his silver chloride paper more sensitive. Fox-Talbot, however, laid claim to priority of discovery, and in an action at law to establish his right he gained the day, although he did so apparently on the technical point that he was the first to make publication of the discovery. That he made an independent discovery of the process, however, there can be no question.
In the Daguerrean process, as we, have seen, the picture was produced upon metal plates, while in that of Fox-Talbot paper alone was used. The former was at first most employed, because the image was clearer than in the other. But the Talbotype (as it was named) soon became the more generally used, especially by amateurs, on account of the cheapness of the paper in comparison with the metal plates required in daguerrotype as well as by reason of the difficulty of obtaining the plates. In 1841 Fox-Talbot had protected his Calotype (i.e. beautiful picture) process by patent; but he subsequently presented his patents to the nation, which of course had the effect of making his process more popular.
In 1842 the Royal Society presented him with its medal in honour of his discovery. His " Pencil of Nature," referred to above, is a collection of landscapes, portraits, facsimiles of engravings and lithographs, etc., produced by his process. In that work he says: " The chief object of the present work is to place on record some of the early beginnings of a new art, before the period, which we trust is approaching, of its being brought to maturity by the aid of British talent." Some of the works thus given to the public will bear comparison with much of the best, and most artistic works of today. Unfortunately they show a tendency to fade—a thing not to be wondered at perhaps when we consider that they are the first fruits of photography.
Amongst other works Talbot published a description of the experiments he made in order to obtain instantaneous photographic pictures (1851), and a notice of his method of engraving on steel by means of light upon a surface composed of gelatine and bichromate of potash in 1853. In the latter, however, to which he gave the name of photoglyphy, he does not appear to have been very successful. Amongst Fox-Talbot's other contributions to photography may be mentioned his introduction of albumen to give a gloss to the surface of paper on which positives are printed.
Gradually the paper process of photography made headway, threatening totally to supersede the daguerrotype method, when, in consequence of certain inconveniences attached to the use of paper—its grain, for instance, and the difficulty of getting it to lie flat in the camera—caused Niepce St. Victor, a cousin of the original discoverer of photography, to turn his attention to glass as a support for the sensitizing material.
St. Victor, like Nicephore Niepce, was a soldier by profession. Nevertheless, he found time to devote considerable attention to scientific study and investigation. It was natural perhaps that his thoughts should turn to photography, and that he should endeavour to perfect the invention with which the name of his family was so intimately identified. He was not the first,, however, to use glass as a support for the sensitive salts of silver, Sir John Herschel having some years before suggested, and even tried, its employment for that purpose.
In order to find out how far organic matter was necessary to the discoloration of silver solutions, Herschel prepared a very diluted solution of salt, which he mixed with muriate of silver. This was poured over a plate of glass, laid at the bottom of a shallow vessel. Gradually the white silver salt was deposited, in the form of a film, on the surface of the glass. The water was then removed by means of a syphon, and the glass left to dry. A solution of silver nitrate was now spread over the film, causing it to become highly sensitive. Exposed in this state in the camera, the silvered glass responded to the light by receiving a faint negative picture. But, although intensified to some extent by electro-deposition, it was found impossible to get good prints therefrom.
These experiments of Sir John Herschel were made public through the Journal of the Royal Society, and no doubt had the effect of turning the attention of many investigators to glass as a support. Amongst the number was Niepce St. Victor, who perceiving that Herschel had failed from not coating his glass plates with a layer of some suitable organic substance to serve as a nidus for the chemical particles to be submitted to the action of light, began experimenting with a view to discovering such a medium. As early as 1847 he had made such progress in the development of his idea as to be able to announce a discovery whereby through the instrumentality of a film of starch, he had succeeded in producing a photograph on glass. Unfortunately his labours were interrupted by the Revolution of 1848, during which troubles the barracks in which he had his laboratory were burned down. Being now for some time on the retired list, he made the most of his enforced leisure to continue his studies, and on the 12th of June 1848 he communicated to the Academy of Sciences his process of photography on glass by the use of albumen.
To make his negative, says M. Tissandier, St. Victor spread upon a plate of glass a thin layer of albumen, which forms a homogeneous coating, smooth and admirably adapted for the purpose required. To sensitize this film of albumen, the inventor saturated it with iodide of silver. For this purpose he plunged it first of all in a bath of iodide of potassium, then in a solution of nitrate of silver. When dry, the sensitized plate of glass served to obtain a negative impression in the camera. When the image was fixed St. Victor found it a comparatively easy matter to obtain positive prints from his glass negative.
This invention of the negative on glass rendered an immense service to photography. Indeed, it produced a complete revolution in the art.
Although M. St. Victor does not appear to have reaped much advantage from his invention, decided step in advancc though it was, in the hands of M. Blanquart-Evrard it produced practical results of a high order. It was soon carried to still greater perfection by M. Le Gray and others.
One of the many improved methods of preparing albumen then in use was as follows:—The whites of five fresh eggs are thrown into a deep dish and carefully beaten together with a whisk or wooden fork for two or three minutes; about 600 grains of iodide of potassium, 20 grains of bromide of potassium, and 10 grains of common salt are then added, and the whole again thoroughly beaten up until it is converted into a white froth. The mixture is then strained through muslin and allowed to remain at rest for ten or twelve hours, when the clear liquid is drained off into a suitable bottle. A sufficient quantity of the iodized albumen is poured on to a plate of glass to cover it with a thin even film. The plate is now allowed to dry spontaneously,,,after which it may be given a final heating before the fire. This hardens the albumen, and puts it in a condition for sensitizing.
This process consists in immersing the prepared side of the plate in a solution composed of nitrate of silver (50 grains), glacial acetic acid (2 drachms), and one ounce of distilled water. The plate may be exposed in the camera whilst still wet, or it may be slightly washed and again dried and exposed in its dry state.
The image is developed by gallic acid in the usual way. If, on development, the image is of a somewhat faint colour, a small quantity of gallic acid and aceto-nitrate of silver, in equal proportions, is poured evenly over it, the tones will be deepened and force and vigour given to the picture.
When the operation has been finished by the application of the hyposulphite of soda, a negative is obtained from which positive impressions may be taken without its being varnished.
The sensitized albumenized plate, thus prepared, might be dried and kept in a dark place till wanted. Indeed dry plates produced by this method were much used by travellers and others.
After the publication of the albumen process many modifications and improvements were suggested, those of the Frenchmen, Blanquart-Evrard and Le Gray, being the most valuable.
Besides the researches which led to his method of photography on glass, St. Victor, following Becquerel, devoted much time to the subject of colour photography, and succeeded in obtaining yellows, blues, reds, and greens, all very vivid, though equally evanescent. He found it impossible to fix them. Exposed to diffused light, they quickly faded.