PHOTOGRAPHY 



PHOTOGRAPHY: THEORY & PRACTICE 



O. E. Brown, F.I.C.. Editor, The British Journal of Photography 

 In this work various articles deal with subjects connected with photo- 

 graphy, e.g. Camera ; Developer ; Lens ; Negative, etc. 



Photography, which essentially 

 is the art or craft of recording the 

 forms of objects by the action of 

 light, was no doubt suggested by 

 the desire to fix the picture or 

 image produced in a camera ob- 

 scura. The first person to suggest 

 definitely the use of a substance 

 sensitive to light for this purpose 

 was Thomas Wedgwood, fourth 

 son of the famous potter. Accord- 

 ing to a paper written in 1802 by 

 Sir Humphry Davy, he rendered 

 paper or leather sensitive to light 

 by soaking in solution of silver 

 nitrate, and so made copies of ferns, 

 etc., by laying the sensitive paper 

 behind them and exposing to 

 light. But he could find no means 

 of preventing further discolora- 

 tion of the copies in daylight. 

 Photography, as a practicable art, 

 had its birth in 1839, when the 

 inventions of six later and inde- 

 pendent experimenters became 

 known, viz. Joseph Nicephore 

 Niepce, Jacques Louis Mande 

 Daguerre, William Henry Fox 

 Talbot, the Rev. J. B. Reade, 

 Hippolyte Bayard, and Sir John 

 Herschel. 



Daguerre's Process 



Niepce began in 1814 and com- 

 pleted about 1829 a process for 

 drawing by light on the litho- 

 graphic stone, metal, etc., and 

 he devised a crude but workable 

 process, depending upon the sen- 

 sitiveness of bitumen (asphaltum) 

 to light, of making intaglio- 

 etched metal plates, from which he 

 took impressions in ink. In 1829 

 he entered into a partnership with 

 Daguerre, whose process was the 

 fixing on a plate of silver or 

 silvered copper of the image of 

 the camera obscura. The silver 

 metal was rendered sensitive by 

 iodine vapour which formed a 

 thin film of silver iodide on it, but 

 the most remarkable feature of 

 the process was Daguerre's dis- 

 covery that the light produced an 

 invisible action upon his sensitised 

 plates. He rendered this latent 

 image visible by exposure of the 

 plate to mercury vapour and 

 thus established a method, which, 

 in altogether different forms, has 

 been universal in photography. 

 Daguerreotypes speedily became 

 the fashion throughout the world, 

 | and remained in vogue until 

 superseded some 15 years later by 

 processes which were the outcome 

 of the British trio of inventors. 



Fox Talbot's experiments began 

 in 1835. He made paper sensi- 

 tive to light with silver nitrate, 



but discovered that he could render 

 prints immune to further action of 

 light by soaking them in a solution 

 of potassium iodide or of common 

 salt (sodium chloride). Talbot 

 made camera pictures by this 

 primitive method and introduced 

 the system of printing positive 

 prints from negatives so produced. 

 Within two years he greatly im- 

 proved the process by making it 

 a development one like Daguerreo- 

 type. This calotype process (q.v.) 

 was patented and exploited by 

 Talbot, and met with some success 

 in competition with Daguerreo- 

 type, but the results, though much 

 cheaper to produce, had not the 

 delicate quality and intrinsic 

 charm of the French process. 

 Herschel 's Improvements 



Herschel's contribution was that 

 of an eminent chemist, who, on hear- 

 ing rumours of Daguerre's inven- 

 tion, promptly set to work to do the 

 same thing. Within a month he 

 worked out a process like Talbot's, 

 but used instead of iodide as the 

 " fixing " agent, the hyposulphite 

 of soda (hypo), which he himself 20 

 years before had shown to be 

 capable of dissolving silver 

 chloride. He now employed it as a 

 means of getting rid of the silver 

 compound not affected by the 

 light. Herschel was apparently 

 the coiner of the words " photo- 

 graph " and "photography" and 

 was the first to use the terms 

 " positive " and " negative " in 

 the now general photographic 

 sense. Reade and Bayard inde- 

 pendently devised means of ren- 

 dering paper sensitive to light. 



Following the calotype process, 

 the next step was towards the use of 

 glass instead of paper in the making 

 of negatives, for the sake of its 

 greater clearness and freedom from 

 impurities. Albumen (white of 

 egg) was used as the medium in 

 which to hold the sensitive , 'silver 

 salts on glass plates, but this and 

 other methods were quickly super- 

 seded by the invention in 1851 by 

 a sculptor, Scott Archer, of the wet- 

 collodion process, which for 30 

 years remained in universal use 

 for making negatives despite its 

 many drawbacks. In it a solution 

 of nitro-cellulose in ether and al- 

 cohol is poured over the glass. 

 This solution is called collodion, 

 which name is applied also to the 

 film left on the glass when the 

 ether and alcohol have evaporated. 

 The collodion contains also iodide, 

 which forms silver iodide when the 

 coated plate is immersed in a bath 



PHOTOGRAPHY 



of silver nitrate. This sensitive 

 plate has to be exposed and devel- 

 oped while wet, and thus calls for 

 a portable dark-room, but at the 

 time it was a great advance 

 on calotype in its greater sensi- 

 tiveness and in the clear and grain - 

 less character of the negatives. 

 The process was also largely used 

 from 1855 for the making of posi- 

 tives little inferior to and much 

 cheaper than Daguerreotypes. It 

 now survives chiefly in the making 

 of negatives for photo-engraving. 



Many attempts were made to re- 

 move the great defect of Scott 

 Archer's process the necessary 

 wetness of the plate for which 

 purpose the collodion coating was 

 treated with various kinds of pre- 

 servatives. None of- these dry 

 collodion plates came into general 

 use, although some came on the 

 market (1856-62) and were the first 

 to be sold completely ready for use. 

 But this form of the process ad- 

 vanced photography through the 

 introduction for it by Major C. 

 Russell in 1862 of an alkaline 

 developer instead of the acid solu- 

 tion previously used. The more 

 powerful action of the alkaline 

 developer was utilised in the next 

 step forward made in 1864 by J. B. 

 Sayce and W. B. Bolton, who 

 succeeded in dispensing with the 

 separate silver sensitising bath. 

 They formed silver bromide in the 

 collodion itself in a state of fine 

 division, i.e. as an emulsion which 

 could be poured on to glass plates. 

 Such plates were then dried, could 

 be carried afield and developed at 

 leisure, thus abolishing the out- 

 door paraphernalia of the wet- 

 plate process. 



Invention of Dry Plates 



In 1871 experiments were begun 

 on the use of gelatin instead of 

 collodion for the preparation of 

 sensitive emulsions. The first dry- 

 plate gelatin emulsion a very im- 

 perfect one was that of Dr. R. L. 

 Maddox. Succeeding experimen- 

 ters sought to produce, not sensi- 

 tive dry-plates, but the emulsion 

 with which photographers were 

 themselves to coat glass, but in 

 1877 plates were put on the market 

 by J. W. (later Sir Joseph) Swan. 



Until 1872 photographic plates, 

 by whatever process prepared, were 

 sensitive only to blue and ultra- 

 violet rays of light. But in that 

 year Dr. H. W. Voppl of Berlin dis- 

 covered that addition of certain 

 dyes to a sensitive collodion 

 emulsion made it sensitive also to 

 green and yellow rays. This prin- 

 ciple was first applied commercially 

 to gelatin emulsion in Germany, 

 where colour - sensitive (ortho- 

 chromatic) plates were used in 

 1883-84. With the invention of new 



