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PHOTOGRAPHY (Gr. bias, light, and ypa...
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See also:PHOTOGRAPHY (Gr. See also:bias, See also:light, and ypa w, to write) , the See also:science and See also:art of producing pictures by the See also:action of See also:light on chemically prepared (sensitized) plates or films . See also:History . It would be somewhat difficult to See also:fix a date when what we now know as " photographic action " was first recorded . No doubt the tanning of the skin by the See also:sun's rays was what was first noticed, and this is as truly the effect of See also:solar See also:radiation as is the darkening of the sensitive See also:paper which is now in use in photographic See also:printing operations . We may take it that K . W . See also:Scheele was the first to investigate the darkening action of sunlight on See also:silver chloride . He found that when silver chloride was exposed to the action of light beneath See also:water there was dissolved in the fluid a substance which, on the addition of lunar See also:caustic (silver nitrate), caused the precipitation of new silver chloride, and that on applying a See also:solution of See also:ammonia to the blackened chloride an insoluble See also:residue of metallic silver was See also:left behind . He also noticed that of the rays of the spectrum the See also:violet most readily blackened the silver chloride . In Scheele, then, we have the first who applied combined chemical and spectrum See also:analysis to the science of See also:photography . In 1782 J . See also:Senebier repeated Scheele's experiments, and found that in fifteen seconds the violet rays blackened silver chloride as much as the red rays did in twenty minutes.' In 1798 See also:Count See also:Rumford contributed a paper to the Philosophical Transactions entitled " An inquiry concerning the chemical properties that have been attributed to light," in which he tried to demonstrate that all effects produced on metallic solution could be brought about by a temperature somewhat less than that of boiling water .
See also:Robert Harrup in 1802, however, conclusively showed in See also:Nicholson's See also:Journal that, at all events, salts of See also:mercury were reduced by visible radiation and not by See also:change of temperature
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In 18or we come to the next decided step in the study of photographic action, when Johann Wilhelm See also:Ritter (1776–1810) proved the existence of rays lying beyond the violet, and found that they had the See also:power of blackening silver chloride
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Such a See also:discovery naturally gave a direction to the investigations of others, and See also: The alteration of colour takes place more speedily in proportion as the light is more intense . " In the See also:direct See also:beam of the sun two or three minutes are sufficient to produce the full effect, in the shade several See also:hours are required, and light transmitted through different-coloured glasses acts upon it with different degrees of intensity . Thus it is found that red rays, or the See also:common sunbeams passed through red glass, have very little action upon it; yellow and green are more efficacious, but blue and violet light produce the most decided and powerful effects." Wedgwood goes on to describe the method of using this prepared paper by throwing shadows on it, and inferentially by what we now See also:call " contact printing . He states that he has been unable to fix his prints, no washing being sufficient to eliminate the traces of the silver See also:salt which occupied the unexposed or shaded portions . Davy in a See also:note states that he has found that, though the images formed by an See also:ordinary See also:camera obscura were too faint to See also:print out in the solar See also:microscope, the images of small See also:objects could easily be copied on such paper . " In comparing the effects produced by light upon muriate of silver (silver chloride) with those upon the nitrate it seemed evident that the muriate was the more susceptible, and both were more readily acted upon when moist than when dry—a fact See also:long ago known . Even in the See also:twilight the colour of the moist muriate of silver, spread upon paper, slowly changed from white to faint violet; though under similar circumstances no intermediate alteration was produced upon the nitrate . . Nothing but a method of preventing the unshaded parts of the delineations from being coloured by exposure to the See also:day is wanting to render this See also:process as useful as it is elegant." In this method of preparing the paper lies the germ of the silver-printing processes of See also:modern times, and it was only by the spread of chemical knowledge that the See also:hiatus which was to render the " process as useful as it is elegant " was filled up—when See also:sodium thiosulphate (hyposulphite of soda), discovered by See also:Francois Chaussier in 1999, or three years before Wedgwood published his paper, was used for making the print permanent . Here we must call attention to an important observation by Seebeck of See also:Jena in 181o . In the Farbenlehre ofGoethe he says: " When a spectrum produced by a properly constructed See also:prism is thrown upon moist chloride of silver paper, if the printing be continued for from fifteen to twenty minutes, whilst a See also:constant position for the spectrum is maintained by any means, I observe the following . In the violet the chloride is a reddish brown (sometimes more violet, sometimes more blue), and this coloration extends well beyond the limit of the violet; in the blue the chloride takes a clear blue tint, which fades away, becoming lighter in the green . In the yellow I usually found the chloride unaltered; sometimes, however, it had a light yellow tint ; in the red and beyond the red it took a See also:rose or See also:lilac tint . This See also:image of the spectrum shows beyond the red and the violet a region more or less light and uncoloured . This is how the decomposition of the silver chloride is seen in this region . Beyond the brown See also:band, . which was produced in the violet, the silver chloride was coloured a grey-violet for a distance-of several inches . In proportion as the distance from the violet increased, the tint became lighter . Beyond the red, on the contrary, the chloride took a feeble red tint for a considerable distance . When moist chloride of silver, having received the action of light for a See also:time, is exposed to the spectrum, the blue and violet behave as above . In the yellow and red regions, on the other See also:hand, it is found that the silver chloride becomes paler; . the parts acted upon by the red rays and by those beyond take a light coloration." This has been brought forward by J . M . Eder as being the first See also:record we have of photographic action lending itself to See also:production of natural See also:colours . This observation of Seebeck was allowed to See also:lie See also:fallow for many years, until it was again taken up and published as a novelty . The first to found a process of photography which gave pictures that were subsequently unaffected by light was Nicephore de See also:Niepce . His process, which he called provisionally " heliographic, dessins, et gravures," consists in coating the See also:surface of a metallic See also:plate with a solution of asphaltum in oil of See also:lavender and exposing it to a camera image .
He recommends that the asphaltum be powdered and the oil of lavender dropped upon it in a See also:wine-glass, and that it be then gently heated
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A polished plate is covered with this See also:varnish, and, when dried, is ready for employment in the camera
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After requisite exposure, which is very long indeed, a very faint image, requiring development, is seen
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Development is effected by diluting oil of lavender with ten parts by See also:volume of white See also:petroleum
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After this mixture has been allowed to stand two or three days it becomes clear and is ready to be used
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The plate is placed in a dish and covered with the solvent
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By degrees the parts unaffected by light dissolve away, and the picture, formed of modified asphaltum, is See also:developed
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The plate is then lifted from the dish, allowed to drain, and finally freed from the remaining solvents by washing in water
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Subsequently, instead of using oil of lavender as the asphaltum solvent, Niepce employed an See also:animal oil, which gave a deeper colour and more tenacity to the surface-film
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Later, See also: Daguerre remarked that " the time required to procure a photographic copy of a landscape is from seven to eight hours, but single monuments, when strongly lighted by the sun, or which are themselves very See also:bright, can be taken in about three hours." Perhaps there is no See also:sentence that illustrates more forcibly the advance made in photography from the days when this process was described . The ratio of three hours to - -hth of a second is a See also:fair estimate of the progress made since Niepce . The development was conducted by means of petroleum-vapour, which dissolved the parts not acted upon by light . As a See also:rule silver plates seem to have been used, and occasionally glass; but it does not appear whether the latter material was chosen because an image would be projected through it or whether simply for the See also:sake of effect . Viewed in the light of See also:present knowledge, a more perfectly developable image in See also:half-See also:tone would be obtained by exposing the film through the back of the glass . The action of light on most organic See also:matter is apparently one of oxidation . In the See also:case of asphaltum or See also:bitumen of See also:Judaea the oxidation causes a hardening of the material and an insolubility in the usual solvents . Hence that surface of the film is generally hardened first which first feels the influence of light . Where half-tones exist, as in a landscape picture, the film remote from the surface first receiving the image is not acted upon at all, and remains soluble in the solvent . It is thus readily seen that, in the case of half-tone pictures, or even in copying engravings, if the action were not continued sufficiently long when the surface of the film farthest from the glass was first acted upon, the layer next the glass would in some places remain soluble, and on development would be dissolved away, carrying the See also:top layer of hardened resinousmatter with it, and thus give rise to imperfect pictures . In See also:carbon-printing-development from the back of the exposed film is absolutely essential, since it depends on the same principles as does heliography, and in this the same mode of See also:procedure is advisable . It would appear that Niepce began his researches as See also:early as 1814, but it was not till 1827 that he had any success See also:worth recounting . At that date he communicated a paper to Dr See also:Bauer of See also:Kew, the secretary of the Royal Society of See also:London, with a view to its presentation to that society . Its publication, however, was pre-vented because the process, of which examples were shown, was a See also:secret one . In an See also:authentic MS. copy of Niepce's " Memoire," dated " Kew, le 8 Decembre 1827," he says that "in his framed drawings made on See also:tin the tone is too feeble, but that by the use of chemical agents the tone may be darkened." This shows that Niepce was See also:familiar with the See also:idea of using some darkening See also:medium even with his photographs taken on tin plates . Daguerreotype.—We have noticed in the See also:joint process of Daguerre and Niepce that polished silver plates were used, and we know from the latter that amongst the chemical agents tried See also:iodine suggested itself . Iodine vapour or solution applied to a silvered plate would cause the formation of silver iodide on those parts not acted upon by light . The removal of the resinous picture would leave an image formed of metallic silver, whilst the black parts of the original would be represented by the darker silver iodide . This was probably the origin of the daguerreotype process . Such observers as Niepce and Daguerre, who had formed a See also:partnership for prosecuting their researches, would not have thus formed silver iodide without noticing that it changed in colour when exposed to the light . What parts respectively Daguerre and Niepce played in the development of the daguerreotype will probably never be known .with See also:absolute accuracy, but in a See also:letter from Dr Bauer to Dr J . J . See also:Bennett . F.R.S., dated the 7th of May 1839, the former says: "I received a very interesting letter from See also:Mons .
Isidore Niepce, dated 12th See also: Over this the plate is placed, See also:face downwards, resting on supports, and the vapour from the iodine is allowed to See also:form upon it a surface of silver iodide . It is essential to note the colour of the surface-formed iodide at its several stages, the varying colours being due to interference colours caused by the different thicknesses of the minutely thin film of iodide . The See also:stage of maximum sensitiveness is obtained when it is of a See also:golden See also:orange colour . In this See also:state the plate is withdrawn and removed to the dark slide of the camera, ready for exposure . A See also:plan frequently adopted to give an even film of iodide was to saturate a card with iodine and hold the plate a See also:short distance above the card . Long exposures were required, varying in See also:Paris from three to See also:thirty minutes . The length of the exposure was evidently a matter of See also:judgment, more particularly as over-exposure introduced an evil which was called " solarization," but which was in reality due to the oxidation of the iodide by prolonged exposure to light . As a matter of history it may be remarked that the development of the image by mercury vapour is said to be due to a See also:chance discovery of Daguerre . It appears that for some time previous to the publication of the daguerreotype method he had been experimenting with iodized silver plates, producing images by what would now be called the "printing out " process . This operation involved so long an exposure that he sought some means of reducing it by the application of different reagents . Having on one occasion exposed such a plate to a camera-image, he accidentally placed it in the dark in a See also:cupboard containing various chemicals, and found after the See also:lapse of a See also:night that he had a perfect image developed . By the process of exhaustion he arrived at the fact that it was the mercury vapour, which even at ordinary temperatures volatilizes, that had caused this intensification of the almost invisible camera-image . It was this discovery that enabled the exposures to be very consider-ably shortened from those which it was found necessary to give in See also:mere camera-printing . The development of the image was effected by placing the exposed plate over a slightly heated (about 75° C.) See also:cup of mercury . The vapour of mercury condensed on those places where the light had acted in an almost exact ratio to the intensity of its action . This produced a picture in an See also:amalgam, the vapour of which attached itself to the altered silver iodide . See also:Proof that such was the case was subsequently afforded by the fact that the See also:mercurial image could be removed by See also:heat . The developing See also:box was so constructed that it was possible to examine the picture through a yellow glass window whilst the image was being brought out . The next operation was to fix the picture by dipping it in a solution of hyposulphite of soda . The image produced by this method is so delicate that it will not See also:bear the slightest handling, and has to be protected from accidental touching . The first great improvement in the daguerreotype process was the resensitizing of the iodized film by See also:bromine vapour . John See also:Frederick Goddard published his account of the use of bromine in See also:conjunction with iodine in 184o, and A . F . J .
See also:Claudet (1797-1867) employed a See also:combination of iodine and See also:chlorine vapour in 1841
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In 1844 Daguerre published his improved method of preparing the plates, which is in reality based on the use of bromine with iodine
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That this addition points to additional sensitiveness will be readily understood when we remark that so-called instantaneous pictures of yachts in full See also:sail, and of large See also:size, have been taken on plates so prepared—a feat which is utterly impossible with the original process as described by Daguerre
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The next improvement in the process was toning or See also:gilding the image by a solution of See also:gold, a practice introduced by H
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L
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See also:Fizeau
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Gold chloride is mixed with hyposulphite of soda, and the levelled plate, bearing a sufficient quantity of the fluid, is warmed by a spirit-See also:lamp until the required vigour is given to the image, as a consequence of which it is better seen in most See also:lights
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Nearly all the daguerreotypes extant have been treated in this manner, and no doubt their permanence is in a great measure due to this operation
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Images of this class can be copied by taking electrotypes from them, as shown by Sir W
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R
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See also:
See also:Fox-Talbot Process.—In January 1839 Fox Talbot described the first of his processes, photogenic See also:drawing, in a paper to the Royal Society
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He states that he began experimenting in 1834, and that in the solar microscope he obtained an outline of the See also:object to be depicted in full See also:sunshine in half a second
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He published in the Philosophical See also:Magazine full details of his method, which consisted essentially in soaking paper in common salt, brushing one See also:side only of it with about a 12% solution of silver nitrate in water, and drying at the See also:fire
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Fox Talbot stated that by repeating the alternate washes of the silver and salt—always ending, however, with the former—greater sensitiveness was attained
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This is the same in every respect as the method practised by Wedgwood in 1802; but, when we come
Albumen Process on Glass.—It was a decided advance when Niepce de St See also:Victor, a See also:nephew of Nicephore de Niepce, employed a glass plate and coated it with iodized albumen
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The originator of this method did not meet with much success
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In the hands of Blanquart Evrard it became more practicable; but it was carried out in its greatest perfection by G
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Le See also: The heat hardens the albumen, and it becomes insoluble and ready for the silver nitrate See also:bath . One of the difficulties. is to prevent See also:crystallization of the salts held in solution, and this can only be effected by keeping them in defect rather than in excess . The plate is sensitized for five minutes in a bath of silver nitrate, acidified with acetic acid, and exposed whilst still wet, or it may be slightly washed and again dried and exposed whilst in its desiccated state . The image is developed by gallic acid in the usual way . After the application of albumen many modifications were introduced in the shape of See also:starch, serum of See also:milk, See also:gelatin, all of which were intended to hold iodide in situ on the plate; and the development in every case seems to have been by gallic acid . At one time the waxed-paper process subsequently introduced by Le Gray was a great favourite . Paper that had been made translucent by white See also:wax was immersed in a solution of potassium iodide until impregnated with it, after which it was sensitized in the usual way, development being by gallic acid . In images obtained by this process the high lights are represented by metallic silver, whilst the shadows are translucent . Such a print is called a " negative." When silver chloride paper is darkened by the passage of light through a negative, we get the highest lights represented by white paper and the shadows by darkened chloride . A print of this See also:kind is called a " See also:positive." See also:Collodion Process.—A great impetus was given to photography to the next process, which he called "calotype " or " beautiful picture," we have a distinct advance . This process Talbot protected by a patent in 1841 . It may be briefly described as the application of silver iodide to a paper support . Carefully selected paper was brushed over with a solution of silver nitrate (See also:ioo grains to the See also:ounce of distilled water), and dried by the fire . It was then dipped into a solution of potassium iodide (50o grains being dissolved in a See also:pint of water), where it was allowed to stay two or three minutes until silver iodide waa formed . In this state the iodide is scarcely sensitive to light, but is sensitized by brushing " gallo-nitrate of silver " over the surface to which the silver nitrate had been first applied . This "gallonitrate " is merely a mixture, consisting of 10o grains of silver nitrate dissolved in 2 oz. of water, to which is added one-See also:sixth of its volume of acetic acid, and immediately before applying to the paper an equal bulk of a saturated solution of gallic acid in water . The prepared surface is then ready for exposure in the camera, and, after a short insolation, develops itself in the dark, or the development may be hastened by a fresh application of the " gallo-nitrate of silver." The picture is then fixed by washing it in clean water and drying slightly in blotting paper, after which it is treated with a solution of potassium bromide, and again washed and dried . Here there is no mention made of hyposulphite of soda as a fixing See also:agent, that having been first used by Sir J . See also:Herschel in February 1840 . In a strictly See also:historical See also:notice it ought to be mentioned that development by means of gallic acid and silver nitrate was first known to Rev . J . B . See also:Reade . When impressing images in the solar microscope he employed gallic acid and silver in See also:order to render more sensitive the silver chloride paper that he was using, and he accidentally found that the image could be developed without the aid of light . The priority of the discovery was claimed by Fox Talbot; and his claim was sustained after a lawsuit, apparently on the ground that Reade's method had never been legally published . Talbot afterwards made many slight improvements in the process . In one of his See also:patents he recognizes the value of the proper fixing of his photogenic drawings by hyposulphite of soda, and also the production of positive prints from the calotype negatives . We pass over his application of albumen to See also:porcelain and its subsequent treatment with iodine vapour, as also his application of albumen in which silver iodide was held in suspension to a glass plate, since in this he was preceded by Niepce de St Victor in 1848 . in 185o, on the introduction of collodion (q.v.), a very convenient vehicle on account of the facility with which the plates are prepared, and also because it is a substance as a rule totally unaffected by silver nitrate, which is not the case with other organic substances . Thus albumen forms a definite silver See also:compound, as do gelatin, starch and gum . The employment of collodion was first suggested by Le Gray, but it remained for Frederick See also:Scott See also:Archer of London, closely followed by P . W . See also:Fry, to make a really See also:practical use of the discovery . When collodion is poured on a glass plate it leaves on drying a hard transparent film which under the microscope is slightly reticulated . Before drying, the film is gelatinous and perfectly adapted for holding in situ salts soluble in ether and alcohol . Where such salts are present they crystallize out when the film is dried, hence such a film is only suitable where the plates are ready to be immersed in the silver bath . As a rule, about five grains of the soluble See also:gun-See also:cotton are dissolved in an ounce of a mixture of equal parts of ether and alcohol, both of which must be of See also:low specific gravity, •725 and •8o5 respectively . If the alcohol or ether be much diluted with water the gun-cotton (pyroxylin) precipitates, but, even if less diluted, it forms a film which is " Grapey " and uneven . Such was the material which Le Gray proposed and which Archer brought into practical use . The opaque silver plate with its one impression was abandoned; and the paper support of Talbot,. with its inequalities of See also:grain and thickness, followed suit, though not immediately . When once a negative had been obtained with collodion on a glass plate—the image showing high lights by almost See also:complete opacity and the shadows by transparency (as was the case, too, in the calotype process)—any number of impressions could be obtained by means of the silver-printing process introduced by Fox Talbot, and they were found to possess a delicacy and refinement of detail that certainly eclipsed the finest print obtained from a calotype negative . To any one who had practised the somewhat tedious calotype process, or the waxed-paper process of Le Gray with its still longer preparation and development, the See also:advent of the collodion method must have been extremely welcome, since it effected a saving in time, See also:money and uncertainty . The rapidity of photographic action was much increased, and the production of a different See also:character of pictures thus became possible . We give an outline of the procedure . A glass plate is carefully cleaned by a detergent such as a cream of See also:tripoli See also:powder and See also:spirits of wine (to which a little ammonia is often added), then wiped with a soft rag, and finally polished with a See also:silk handkerchief or See also:chamois leather . A collodion containing soluble iodides and bromides is made to flow over the plate, all excess being drained off when it is covered . A See also:good See also:standard See also:formula for the collodion is—55 rains of pyroxylin, 5 oz. of alcohol, 5 oz. of ether; and in this liquid are dissolved 21 grains of ammonium iodide, 2 grains of See also:cadmium iodide and 2 grains of cadmium bromide . When the collodion is set the plate is immersed in a bath of silver nitrate—a See also:vertical form being that mostly used in England, whilst a See also:horizontal dish is used on the |