[The original letter has not been located. This was published in The Athenaeum, no. 1258, 6 December 1851, pp. 1286-1287. A few days earlier, WHFT had submitted essentially the same text (either in French or translated into French) to the Compte Rendus des Séances de l'Académie des Sciences, session of 1 December 1854, v. 33 no. 22, 1851, pp. 623-627. See Doc. No: 06493.]
ON THE PRODUCTION OF INSTANTANEOUS PHOTOGRAPHIC IMAGES.
It will probably be in the recollection of some of your readers that in the month of June last a successful experiment <1> was tried at the Royal Institution in which the photographic image was obtained of a printed paper fastened upon a wheel, the wheel being made to revolve as rapidly as possible during the operation.
From this experiment the conclusion is inevitable, that it is in our power to obtain the pictures of all moving objects, no matter in how rapid motion they may be, provided we have the means of sufficiently illuminating them with a sudden electric flash. But here we stand in need of the kind assistance of scientific men who may be acquainted with methods of producing electric discharges more powerful than those in ordinary use. What is required, is, vividly to light up a whole apartment with the discharge of a battery: -the photographic art will then do the rest, and depict whatever may be moving across the field of view.
I had intended to communicate much earlier the details of this experiment at the Royal Institution, but was prevented from doing so at the time, -and soon afterwards I went on the Continent in order to observe the total solar eclipse of the 28th of July. This most interesting phenomenon I had the pleasure of witnessing at the little town of Marienburg, in the northeastern corner of Prussia. The observations will appear, I believe, in a forthcoming volume of the Transactions of the Royal Astronomical Society.<2> Among other things, I was enabled to make a satisfactory estimate of the degree of darkness during the total obscuration; which proved to be equal to that which existed one hour after sunset the same evening, the weather being during that evening peculiarly serene, so as to allow of a just comparison.
This Continental journey having effectually interrupted my photographic labours, I have only recently been able to resume them. I shall, therefore, now proceed to describe to you exactly the mode in which the plates were prepared which we used at the Royal Institution: at the same time not doubting that much greater sensibility will be attained by the efforts of the many ingenious per sons who are now cultivating the art of photography. And it is evident that an increased sensibility would be as useful as an augmentation in the intensity of the electric discharge.
The mode of preparing the plates is as follows.-
1. Take the most liquid portion of the white of an egg, rejecting the rest. Mix it with an equal quantity of water. Spread it very evenly upon a plate of glass, and dry it at the fire. A strong heat may be used without injuring the plate. The film of dried albumen ought to be uniform and nearly invisible.
2. To an aqueous solution of nitrate of silver add a considerable quantity of alcohol, so that an ounce of the mixture may contain three grains of the nitrate. I have tried various proportions, from one to six grains, but perhaps three grains answer best. More experiments are here required, since the results are much influenced by this part of the process.
3. Dip the plate into this solution, and then let it dry spontaneously. Faint prismatic colours will then be seen upon the plate. It is important to remark, that the nitrate of silver appears to form a true chemical combination with the albumen, rendering it much harder, and insoluble in liquids which dissolved it previously.
4. Wash with distilled water to remove any superfluous portions of the nitrate of silver. Then give the plate a second coating of albumen similar to the first; but in drying it avoid heating it too much, which would cause a commencement of decomposition of the silver. I have endeavoured to dispense with this operation No. 4, as it is not so easy to give a perfectly uniform coating of albumen as in No. 1. But the inferiority of the results obtained without it induces me for the present to consider it as necessary.
5. To an aqueous solution of prot-iodide of iron add first an equal volume of acetic acid, and then ten volumes of alcohol. Allow the mixture to repose two or three days. At the end of that time it will have changed colour, and the odour of acetic acid as well as that of alcohol will have disappeared, and the liquid will have acquired a peculiar but agreeable vinous odour. It is in this state that I prefer to employ it.
6. Into the iodide thus prepared and modified the plate is dipped for a few seconds. All these operations may be performed by moderate daylight, avoiding however the direct solar rays.
7. A solution is made of nitrate of silver, containing about 70 grains to one ounce of water. To three parts of this add two of acetic acid. Then if the prepared plate is rapidly dipped once or twice into this solution it acquires a very great degree of sensibility, and it ought then to be placed in the camera without much delay.
8. The plate is withdrawn from the camera, and in order to bring out the image it is dipped into a solution of protosulphate of iron, containing one part of the saturated solution diluted with two or three parts of water. The image appears very rapidly.
9. Having washed the plate with water, it is now placed in a solution of hyposulphite of soda; which in about a minute causes the image to brighten up exceedingly, by removing a kind of veil which previously covered it.
10. The plate is then washed with distilled water, and the process is terminated. In order, however, to guard against future accidents, it is well to give the picture another coating of albumen or of varnish.
These operations may appear long in the description, but they are rapidly enough executed after a little practice. In the process which I have now described, I trust that I have effected a harmonious combination of several previously ascertained and valuable facts,- especially of the photographic property of iodide of iron, which was discovered by Dr. Woods, of Parsonstown, in Ireland,<3> and that of sulphate of iron, for which science is indebted to the researches of Mr. Robert Hunt.<4> In the true adjustment of the proportions, and in the mode of operation, lies the difficulty of these investigations; since it is possible by adopting other proportions and manipulations not very greatly differing from the above, and which a careless reader might consider to be the same, not only to fail in obtaining the highly exalted sensibility which is desirable in this process, but actually to obtain scarcely any photographic result at all.
To return, however, from this digression.- The pictures obtained by the above-described process are negative by transmitted light and positive by reflected light. When I first remarked this, I thought it would be desirable to give these pictures a distinctive name, and I proposed that of Amphitype,<5> as expressive of their double nature,- at once positive and negative. Since the time when I first observed them, the Collodion process has become known, which produces pictures having almost the same peculiarity. In a scientific classification of photographic methods, these ought therefore to be ranked together as species of the same genus.<6> These Amphitype pictures differ from the nearly related Collodion ones in an important circumstance, viz., the great hardness of the film and the firm fixation of the image, which is such that in the last washing, No. 10, the image may be rubbed strongly with cotton and water without any injury to it; but, on the contrary, with much improvement, as this removes any particles of dust or other impurity, and gives the whole picture a fresh degree of vivacity and lustre. A daguerreotype picture would be destroyed by such rough usage before it was completely fixed and finished.
In examining one of the Amphitype pictures, the first thing that strikes the observer is, the much greater visibility of the positive image than of the negative one, which is at least in the proportion of ten to one,- since it is not rare to obtain plates which are almost invisible by transmitted light, and which yet present a brilliant picture foil of details when seen by reflected light.
The object of giving to the plates a second coating of albumen, as prescribed in No. 4, is chiefly in order to obtain this well-developed positive image; for it is a most extraordinary fact, that a small change in the relative proportions of the chemical substances employed enables us at pleasure to cause the final image to be either entirely negative or almost entirely positive. In performing the experiment of the rotating wheel the latter process must be adopted; since the transmitted or negative image is not strong enough to be visible unless the electric flash producing it be an exceedingly bright one.
I now proceed to mention a peculiarity of these images which appears to me to justify still further the name of Amphitype, or, as it maybe rendered in other words, "ambiguous image." Until lately I had imagined that; the division of photographic images into positive and negative was a complete and rigorous one, and that all images must be of either the one or the other kind. But a third kind of image of a new and unexpected nature is observed upon the Amphitype plates. In order to render this intelligible, I will first recall the general fact that the image seen by transmitted light is negative and that by reflected light positive. Yet, nevertheless, if we vary the inclination of the plate, holding it in various lights, we shall not fail speedily to discover a position in which the image is positive although seen by transmitted light. This is already a fact greatly requiring explanation. But the most singular part of the matter is, that in this new image (which I call the transmitted positive), the brightest objects (viz. those that really are brightest, and which appear so in the reflected positive) are entirely wanting. In the places where these ought to have been seen, the picture appears pierced with holes, through which are seen the objects which are behind. Now, if this singularity occurred in all the positions in which the plate gives a positive image, I should be satisfied with the explanation that the too great brightness of the objects had destroyed the photographic effect which they had themselves at first produced. But since this effect takes place in the transmitted positive but not in the reflected positive, I am at a loss to suggest the reason of it, -and can only say that this part of optical science, dependent upon the molecular constitution of bodies, is in great need of a most careful experimental investigation.
The delicate experiment of the revolving wheel requires for its success that the iodide of iron employed should be in a peculiar or definite chemical state. This substance presents variations and anomalies in its action which greatly influence the result. Those photographers, therefore, who may repeat the experiment will do well to fix their principal attention upon this point. It is also requisite in winter to warm the plates a little before placing them in the camera. In pursuing this investigation, I have been much struck with the wide field of research in experimental optics which it throws open. By treating plates of albumened glass with different chemical solutions, the most beautiful Newtonian colours, or colours of thin plates, may be produced. And it often happens that the landscapes and pictures obtained by the camera present lively though irregular colours. These not being in conformity with nature are at present useless; with this exception, nevertheless, that in many pictures I have found the colour of the sky to come out of a very natural azure blue. I hope soon to have the leisure requisite for pursuing this very interesting branch of inquiry, and in the mean time I venture to recommend it to the notice of your scientific readers.
I am, &c.,
H. F. Talbot
2. WHFT's account was ‘Observations on the Total Eclipse of the Sun on July 28, 1851. Marienburg, Prussia’, Memoirs of the Royal Astronomical Society, v. 21 part 1, 1851–1852, pp. 107–113. He also described his experience in private letters to two old friends, the French scientist Jean-Baptiste Biot (1774-1862) Doc. No: 06448; and to Sir John Frederick William Herschel (1792-1871), astronomer & scientist -Doc. No: 06460.
3. Dr Thomas Woods (1815-1905), Irish physician, photographer, inventor & friend of Lord Rosse. Woods published 'On the Electrolysotype; a new Photographic Process', Report of the British Association for the Advancement of Science, 1844, section 2, pp. 36-37. Woods used a sugar syrup solution of ferric iodide and a solution of silver nitrate to make a negative paper, one he felt was sufficiently sensitive to take portraits in the shade in fifteen seconds, and a picture of moonlight in fifteen minutes. The exposed negative would develop spontaneously in the dark, a process he ascribed to electrolysis.
4. Robert Hunt (1807-1887), scientist & photographic historian. Hunt published this as the 'Energiatype: A New Photographic Process', Athenæum, no. 866, 1 June 1844, pp. 500-501. In September, Hunt elaborated on this process at the BAAS meeting, changing its name: 'On the Ferrotype, and the Property of Sulphate of Iron in developing Photographic Images'. Talbot responded to Hunt's presentation, outlining his own experiments with iron, pointing out that the spontaneous development was in fact how he first discovered the calotype process, and feeling that Woods' process was only a variation on the calotype. Report of the British Association for the Advancement of Science, 1844, pt. 2, pp. 36 and 105.
5. In an 1843 letter, Doc. No: 04784, WHFT suggested that Herschel call his process Amphitype, which advice Herschel took in Doc. No: 04788. Herschel never could resolve this process that led him ‘such a dance’, and he relinquished the name for WHFT’s own use in Doc. No: 06418. The name Amphitype became more widely known as an alternative for direct positives in collodion (ambrotypes).
6. This observation, which gives some insight into how WHFT regarded the rival wet collodion process, is usually overlooked in discussions about the challenges to his calotype patent that were arising in this period.