rnOTOORAPHT. 



PHOTOGRAPHY. 



KitraU of Silver ; with Observation* by H. D*rf .' ThU paper con- 

 Uiiu UM complete genus of the photographic rt, namely, the applies- 

 : an optical instrument to imprint upon sensitive chemical 

 surface UM image* of all natural object* illuminated l>y the sunbeam, 

 or other aouroi of light. The iiutrumrnU used by thM* observer* 

 were thu camera obscura and the eolar niicroecope : but let ua first tee 

 bow this important invmtion took ahape in the mind of Wedgwood. 



According to 1'avy, Wedgwood Brat commenced bia researched with 

 a view to copy the image* of the camera oliacura ; and for this pur 

 poee, say* Davy, " ho first used nitrate of ailver. whioh wa* mentioned 

 to him tv a fnend a* a Bubatanoa very sensible to the influence of 

 light." This nitrate of ailver wna applied in solution to surface* 

 of white paper and leather. " White paper or white leather," to 

 quote the words of the memoir of 1802, " moutenid with > 

 at nitrate of silver, undergoes no change whtn kept in a dark place ; 

 . being exposed to the daylight, it speedily change* colour, and, 

 after passing through different shades of grey and brown, become* at 

 length nearly black. The alteration* of colour take place more 

 speedily in proportion a* the light ia more intense. In the direct 

 beam of the un two or three minute* are sufficient to produce the 

 full effect; in the (hade several hour* are required ; and light trans- 

 mitted through different coloured glasses act* upon it with different 

 degree* of intensity." . . . . " When the thadnw of any figure i* thrown 

 upon the prepared em-face, the part concealed by it remain* white, and 

 the other part* speedily become dark. For copying painting* on glai* 

 the solution ahould be applied on leather, and in this case it ia more 

 readily acted on than when paper is used. After the colour ha* been 

 once fixed on the leather or paper, it cannot be removed by the appli- 

 cation of water, or water and *oap ; and it i* in a high degree per- 

 nt. The copy of a painting, or the profile, immediately after being 

 taken must be kept in an obscure place ; it may, indeed, be examined 

 in the ahade, but in this case the exposure ahould be only for a few 

 minute* : by the light of candle* or lamp*, as commonly employed, it 

 i* not sensibly affected." No mean* were found to fix permanently 

 the impressions thus produced. And, a* regards the primary end of 

 Wedgwood's researches, we are told that " The image* formed by 

 means of a camera obscura have been found to be too faint to 

 produce in any moderate time an effect upon the nitrate of silver." 

 Davy adds, "In following these processes, I have found that the 

 images of small object* produced by means of the solar microscope, 

 may be copied without difficulty on prepared paper. This will pro- 

 bably be n useful application of the method ; that it may he employed 

 successfully, however, it is necessary that the paper be placed at but 

 a small distance from the lens." 



The muriate (chloride) of silver was found to be more sensitive to 

 light than the nitrate. " Even in the twilight, the colour of the moist 

 muriate of silver spread upon paper slowly changed from white to 

 faint violet ; though under similar circumstances no immediate alte- 

 ration was produced upon the nitrate." Davy concludes with those 

 remarkable words: "Nothing but a method of preventing the un- 

 shaded parts of the delineations from being coloured by exposure to 

 the day, is wanting to render this process as useful as it is elegant." 



From this time the art in England slumbered until 1834, when 

 Mr. Fox Talbot, without knowing what had been done, commenced 

 experiments with the same end in view. 



But we must now turn to a neighbouring country, France. In 1813, 

 M. Niepce, of Chalons on the Saone, was engaged in a task identical 

 in conception with that of Wedgwood. He was endeavouring, by 

 mean* of bituminous varnishes and metal plates, to fix permanently 

 the images of the camera, and he lucceeded to a remarkable extent. 

 His experiment* were carried on until 1827, in which year he presented 

 a memoir with specimens to the lloyal Society of London ; but, as he 

 kept hi* processes secret, no notice was taken of his labours. Nidpce 

 returned to France dispirited. He there, however, continued hia 

 experiment*, making pictures on a surface of bitumen laid upon a 

 : plate, which he afterwards engraved by ordinary engraver's 

 acid. 'I In- ia'i..n.i|o of bin process is tliis : Light is capable of harden- 

 ing a bituminous surface in such a way that the usual solvents of 

 lougi-r net ivadily upon the altered part of the surface, and 

 s of a partially illuminated plate 



Would yiel-i t-. >iicli s Ivi-nu as the mineral naphthas, for example, 

 furnish. But when a metal plate had been partially laid bare by the 

 removal of the bitumen in the shadows, nothing wa* easier than to 

 eU-h mich a plate by aqua fortis, and this was what Nie"pce did. A 

 ]iUte thus made and print* from it were in the possession of the late 

 .Mr. Hubert Brown, .if tlic British Muraum. It i* to be hoped that 

 how) in the Museum iUolf. M. Nicpce named his art 

 Hitiaansj 



In 1H2WM. Nicpce became acquainted with a M. Dagucrre [DAGUEIIBE, 



L. . J. M., in Bioo. Dnr.L who wa* noted for his dioramio paintings, and 



> wa*, it u alleged, also engaged upon methods for fixing the image* 



A deed ..f partnership was executed between ' 

 -!U. ami they jointly pumied their labour* until the death 

 July, 1833. A new arrangement wa* then made bctw , . u 

 Li* son, M. Isidore Nie|>ce and Itaguerrc. 



At length came the memorable year 1830, when the whole scientific 



Irtic world was startled at the announcement that object* could 



be mad* to draw their own picture* with an accuracy and minutenei* 



quit* unattainable by hand. In January, 1 889, the*nr*t spoctmeru by 

 Uaguerre were shown, but the process was withheld until the month 

 of July. Thi* en*bltxl Mr. Fox Talbot to secure to himself tin 

 of priority of publication of a method by which inn-drawn picture* 

 could lie successfully produced. Me, on the 18th of January, com- 

 muniotUd to the lloyal Society a paper, entitled ' Some Account of 

 til* Art of Photogenic Drawing, or the Process by which Natural 

 Object* may be made to delineate themselves without the AM of the 

 Artist's Pencil.' And on the 21st of February in the came year, he 

 gave another communication on the method of preparing sensitive 

 paper and of fixing the image* obtained. That the two experi- 

 mentalist*, Talbot and Daguerre, were independent discoverers is 

 evident from the dissimilarity of their processes ; the light and camera 

 obscura being the only mean* strictly in common. 



Mr. Talbot'* method consisted in washing lutter-paper over repeat- 

 edly with alternate *olution* of aalt and nitrate of silver ; at a certain 

 stage a surface was obtained which gave images under thu influence of 

 the camera, and these image* were fixed by immersion in a strong 

 solution of salt and water, in which the unaltered parts of tho 

 chloride of ailver were soluble. Thi* process wa* not very sensitive, 

 and wa* therefore act aside by Mr. Talbot'* later discoveries of 1840. 



Let us now examine the nature of Daguorre's process called the 

 Daguerreotype. A plate of silvered copper is highly polished, and than 

 exposed to the vapour of the chemical element iodine, which impart* 

 1 1 the plate a series of colours, depending on the quantity of iodine 

 absorbed. The exposure to the vapour was carried on until the plate 

 assumed a rosy tint, or simply a deep orange-yellow, bordering on red. 

 The plate was now sensitive, and had only to be exposed at the focus 

 of the camera obscura in order to obtain a picture of any strongly 

 illuminated object. Some minutes were necessary even in full sun- 

 shine. The plate was then withdrawn into the darkened room in 

 which it had been prepared, and there it wa* exposed to the vapour of 

 heated mercury, which has the wonderful property of attaching itself 

 only to those part* of the iodised plate which have been exposed to 

 light ; and this deposit take* place in proportion to the < 

 intensity of light of the image. Thus a picture waa produced 

 represented in shades of black and white the original optical image 

 seen on the ground-gloss screen of the camera. 



A solution of the hyposulphite of soda wo* used to fix the image by 

 removing the compound of iodine and silver which still veiled in some 

 degree the shadows on the plate. Subsequently M. Fizeau improved 

 the appearance of Daguerreotypes by imparting to them a warm tinge 

 by a thin film of gold which was thrown down upon the image by a 

 spontaneous electro-chemical action. 



The original Daguerreotype process was not sufficiently sensitive to 

 be used in portraiture. To Mr. Ooddard, who deserves reward, we owe 

 the great improvement of the introduction of a second chemical agent, 

 which now enable* us to make pictures in a second of time. In 1840 

 Mr. Goddard combined bromine with iodine, and at once published the 

 result in the ' Athenaeum ' journal. In the dull weather of November 

 of that year, he obtained portraits in a few seconds ; Daguerre's process 

 requiring many minutes, even in a strong light. Mr. Claudet, at a later 

 date, used chlorine with iodino for a similar end ; but the bromine ia 

 still used in preference. 



One of the beat modes of procedure now adopted is the following : 

 Take a plate of silvered copper and polish it by moan* of tripoli 

 powder and oil of lavender or rosemary, applied by cotton velvet, 

 finishing the polish by clean cotton velvet alone. Then expose the 

 silver to a mixture of iodine and pure sand in such a manner that the 

 vapour of the iodine shall act equally upon the surface of the silver 

 plate, to which it imparts a coating which is seen to be coloured when 

 examined by light reflected from any white surface, a piece 01 

 for example. As soon as the plate has assumed an orange-yellow 

 colour it in removed, and then exposed to the vapour issuing from a 

 jiecnliar red compound of bromine with lime, called " bromide of 

 lime." Over this it absorbs bromine, aud assumes a rose tint; and a* 

 soon as this shade of colour has been obtained, the plate must be 

 removed and again exposed to the iodino vessel until the rose colour 

 i has deepened into a plum tint. The plate U then ready for exposure 



in ilir ramrra obscura. Mo time can be stated for these \ 

 i exposures, as temperature inlluences the result*. A few seconds in 

 each case suffice. The plate must be prepared in a room which can be 

 darkened, the light of a candle, or that obtained through yellow glass, 

 being alone used at the lost iodising, and in some of the subsequent 

 operations. After exposure in the camera, the plate is exposed to the 

 vapour of mercury for a few minutes, the mercury being at a. tempe- 

 rature of about 180 Fahr. Here the picture is developed by the 

 action of the mercury upon the bromo-iodised surface, the mercury 

 being, it is believed by some, deposited upon the plate in proportion to 

 the amount of light which fell upon its surface during ite exposure in 

 the camera. On it* removal from the mercury box the plate ia 



ly fixed by washing its surface with a strung solut 

 sulphite of wxia. The final fixation is effected by boil.' 

 plate a solution of a double salt, called hyposulphite of so-l.-i :m.l voi'l. 

 ., fixed u|H>n the plate, and mny be coloured dy 

 nig over it colours in very fine powder. The image abouM lie 

 kept so a* to exclude the vapours of an impure atm h an is 



uually found in largo town*. Sulphuretted vapour* will at once 



