PHOTOGRAPHY. 



PHOTOGRAPHY. 



470 



darken the light part of the image. The film of stain may, however, 

 generally be removed by a solution of cyanide of potassium. The 

 Daguerreotype is still unsurpassed in delicacy of detail. 



Having given an account of the Daguerreotype, we might proceed to 

 relate the history of Mr. Fox Talbot's researches, which led to the 

 invention of the first successful process in photography on paper; but 

 as these will be found detailed in Mr. Talbot's work ' The Pencil of 

 Nature,' and in the specifications of his patents, we prefer to pass at 

 once to consider a process which has now almost superseded all others, 

 and which certainly sprang out of Mr. Fox Talbot's discoveries. Mr. 

 Talbot used iodide of silver with nitrate of silver in excess, upon paper, 

 for the purpose of procuring an image which remained latent until 

 developed by a solution of gallic acid. The process now used, and 

 called the Collodion process, of Mr. Scott Archer, consists in the use of 

 a film, on glass, of collodion, containing also iodide of silver with an 

 excess of nitrate, the development being accomplished by pyro-gallic 

 acid, or by sulphate of iron, the use of which we owe to Mr. B. Hunt, 

 in the place of gallic acid. The analogy ia complete, but the latter 

 materials give a greater delicacy of result. 



Collodion is made by dissolving in ether and alcohol cotton-wool 

 which has been altered in its properties by treatment with strong acids. 

 The following ia a good mode of proceeding, and is due mainly to the 

 researches of Mr. Hadow.* Take of pure nitrate of potash in fine 

 powder 510 grains, of oil of vitriol (specific gravity 1-S33 about) 15} 

 drachms, of water 1J drachm ; stir together, and when at a tempe- 

 rature of from 150 to 155 Fahr. add, bit by bit, 15 grains of cotton- 

 wool to each ounce of the acid mixture. Allow the cotton to soak for 

 four or five minutes, and then wash it many times in water until it is 

 quite free from acid. Then, to make the collodion, take 9 grams of 

 the dry cotton, and add 6 drachms of pure ether (sp. gr. "725 to '730), 

 and 2 drachms of pure alcohol (sp. gr. '818 to '820). The cotton should 

 at once dissolve. In another bottle prepare what is called the " iodising 

 solution," by taking alcohol (sp. gr. '818 to -820) one ounce, iodide of 

 potassium 12 grains, iodide of cadmium 4 grains ; dissolve the salts in 

 the alcohol, and keep the solution for use. To make " iodised collodion," 

 mix 6 drachms of collodion with 2 drachms of the iodising solution ; 

 this mixture changes by keeping, and should therefore be made only 

 in moderate quantities. Having prepared the iodised collodion, a plate 

 of glass is covered with it by pouring a quantity on the centre of the 

 plate, and then allowing the liquid to flow to the corners in such a way 

 that the glass shall be uniformly covered ; the excess ia then run oft' at 

 one comer into a bottle set apart for the purpose. After a few seconds 

 the film of iodised collodion is sufficiently firm to be fit for immersion 

 (in the dark) in what is called the " nitrate bath." This bath is made 

 by dissolving 30 grains of nitrate of silver in one ounce of distilled 

 water. The nitrate of silver should be pure, and free from excess of 

 nitric acid, and it should be saturated, when in solution, with iodide of 

 BilTer : a little acetic acid, too, may be added. The plate is immersed 

 in this bath for a few minutes, drained, and then exposed in the camera 

 obscura. To develope the image, a solution of pyrogallic acid con- 

 taining one grain of the salt to one ounce of water acidulated by 

 20 drops, or Tninimii, of glacial acetic acid is poured upon the plate. 

 If the image is not intense enough, a little weak solution of nitrate of 

 silver must be added. The image obtained is fixed by a strong solution 

 of hyposulphite of soda, in which it is immersed ; or, instead, a weak 

 solution of cyanide of potassium may be poured upon the plate, and 

 left there until the yellow film of iodide of silver disappears. The 

 plate is then washed and dried, and protected by a film of varnish, a 

 spirit varnish being usually preferred for this purpose. 



The picture thus obtained is, as in the calotype or Talbotype pro- 

 cess of Mr. Fox Talbot, a neijative one that is to say, a picture having 

 iU light and shade reversed; though by modifying the collodion 

 process direct positives may be at once obtained : a good negative, 

 however, is a more valuable acquisition. In order to obtain copies 

 correct in light and shade and position, a potitive has to be made. 

 There are many processes by which this can be done ; but we will here 

 give only one, which answers perfectly. Take the white of a fresh egg 

 and beat up with every fluid ounce of it 12 grains of common salt : 

 remove the froth thus obtained, and continue beating until all has 

 become froth. Leave this froth to itaelf, and the greater part of the 

 white of egg will become again liquid. Pour this liquid into a flat 

 shallow dish, and upon it place carefully, so as to exclude bubbles of 

 air, a sheet of thin paper ( French paper is usually chosen) ; leave the 

 paper for two or three minutes floating, BO as to coat only one side 

 with the " Baited albumen," as the white of egg mixture is now called. 

 Then carefully mm ve the sheet, and pin it up by a corner to dry. 

 This operation can be carried on in daylight. To make this ]per 

 sensitive, it is iloattd upon a solution ot nitrate of silver containing 

 100 grains of nitrate to one ounce of water. Here it is left for a 

 minute, and then n moved and suspended to dry. This last operation 

 must be performed in a room lighted by yellow light, as in the case 

 of the daguerreotype and collodion final preparation. Upon the-dry 

 paper the negative picture is placed face to face, and the whole exposed 

 in a proper ' pressure-frame ' to the sun or to daylight, or to the 

 electric light for ten minutes or a qnarter of an hour by night. After 



8*0 alo Mr. Hardwich's formula in the 'Journal of the Photographic 

 Book'tf' for 1360. 



a few minutes the picture is found printed, and must next be fixed by 

 immersion in a solution of hyposulphite of soda, one part of the salt 

 in four parts of water. Ten or fifteen minutes' immersion would 

 suffice to fix the picture ; but in order to produce an agreeable tint of 

 colour, a longer immersion ia had recourse to, with the addition to the 

 ' fixing bath " of a few grains of a neutral solution of chloride of gold. 

 After several hours' immersion in thii bath, the picture is removed, 

 and washed repeatedly with plenty of water ; hot distilled water being 

 used at last. This fixing bath is made fresh for each day's work. The 

 pictures, when washed and dried, may be mounted on cardboard by 

 means of starch, gum, or gelatine ; paste is supposed to injure the 

 picture under some circumstances. Exposure of the finished picture to 

 impure atmutplieric vapourt, and to damp, is to be avoided. Mr. Malone 

 has advised that the picture should be heated in a solution of caustic 

 potash in order to secure its greater permanency. He also insists on 

 the injurious action of sulphur in certain forms upon the print. 



The process just described yields perfect results, arul has super- 

 seded all others for the purpose of making Photogenic Drawings,' as 

 they wore formerly termed. Leaves, grasses, prints, feathers, lace, and 

 indeed any well-defined object, translucent or not, may be depicted by 

 simple contact with the prepared paper and subsequent exposure of 

 the whole to light, under a sheet of glass pressed tightly on by springs 

 or screws, as in the ordinary ' copying-frame.' In the absence of the 

 sun, a quarter of an hour's exposure to the electric light will produce a 

 good positive impression. 



There is another branch of photography which is worthy of the 

 attention of the student, but which has not yet come into practical 

 operation in a perfectly satisfactory manner. It ia that of photographic 

 engraving. The labours of Niepce, Grove, Fizeau, Talbot, Pretsch, 

 Poitevin, and others have done much to forward this art, and are well 

 worthy of attention. Although the first Niepce laid the foundation of 

 the art of Photographic Engraving, by his experiments on asphalt um, 

 or Jew's pitch, it is to Mr. Talbot that we are indebted for opening 

 up new processes hi which organic substances such as starch, gum, 

 albumen, and gelatine mixed with a salt of chromic acid furnish a 

 photographic deposit which is capable of being worked by the ordinary 

 processes of the engraver and lithographer. Mr. Talbot's plan is to 

 pour upon a steel plate a mixture of bi-chromate of potash and 

 gelatine, so as to obtain by drying a sensitive film : upon this film a 

 positive photographic drawing is placed ; now, by exposure to light, 

 the gelatine becomes hardened, or nearly insoluble wherever the light 

 has fallen through the positive picture. An engraving acid poured 

 upon the plate will now etch only the shaded parts of the plate, and 

 thus an engraved surface is obtained to be printed from with printer's 

 ink. Mr. Pretsch, instead of etching the plate obtained by the action 

 of the light on the gelatine compound, acts upon it by liquids ; and 

 what is most remarkable, gets a grained image in relief from which a 

 mould is taken for the purpose of being electrotyped to form the 

 copper-plate to print from. By proper manipulation, Mr. Pretsch can 

 produce plates fit to print by the method called surface-printing, as 

 with an ordinary wood block. 



Of course, impressions taken from these plates by proper means can 

 be conveyed to porcelain or glass, and burnt in by the euameller in the 

 usual manner, or as at first devised by Mr. Malone, and described in 

 a jouit patent taken out with Mr. Talbot. To Messrs. Ponton and 

 Becquerel we owe the first application of chromium to general photo- 

 graphic purposes. Mr. Pauncey and others have also devised ingenious 

 processes by which pigments or inks may be made to adhere only tc 

 the altered gelatine and chromium compound surface, whether on 

 paper, stone, glass, porcelain, or metals. These processes are as yet 

 under trial. They lack the delicacy of tint of the albumen process, 

 but they will doubtless yield ultimately valuable results. 



Stimulated by the experiments of Sir John Herschel, M. Ed. Bee- 

 quercl and others, M. Nidpce de St. Victor commenced a series of 

 beautiful experiments upon coloured flames and their photographic 

 images. He laid before the Academy of Sciences, Paris, a detailed 

 memoir upon the subject on the 4th of March, 1851. This was 

 followed by others on June 2, 1851, Fub. 9, 1852, and November 6, 

 1852. By the method described in these papers, M. Niepce succeeded, 

 he says, in obtaining upon silver plates which had been rendered 

 sensitive by a chloride of copper, images which faithfully reproduced 

 the colours in coloured engravings, flowers both artificial and natural, 

 lay-figures dressed in stuns and gold and silver lace, precious stones, 

 &c. These were obtained both by the process of photographic printing 

 and in the camera ; the lij;ht and brilliant colours being obtained with 

 comparative ease, but the darker and more sombre colours more 

 slowly. The colours he rendered more vivid and at the same time more 

 lasting by the action of ammonia. But beautiful as were the results, 

 and much more nearly than in any other previous experiments as 

 they seemed to approach the solution of the problem of photographing 

 the colours of nature, they proved to be only comparatively permanent. 

 The colours soon began to fade and eventually disappeared altogether. 

 This method (due to M. Ed. Becquerel) M. NiiSpce named Heliochrome. 

 M. Ed. Becquerel, by the use of silver plates, coated with a dark 

 compound of chlorine and silver, obtained by the voltaic decom- 

 position of hydrochloric acid, has succeeded in obtaining coloured 

 images of the solar spectrum, but no method of fixing them permanently 

 has been discovered. 



