CHAMBERS'S INFORMATION FOR THE PEOPLE. 



of copies may be printed in the lithographic 

 press. 



A method of carbon-printing, which gives very 

 beautiful results, was patented some years ago by 

 Mr Woodbury, and is known as ' Woodburytype.' 

 An image in relief is obtained on a bichromatised 

 gelatine film, and laid on a plate of soft metal. 

 On this is placed a plate of polished steel, and 

 the whole subjected to hydraulic pressure, which 

 forces every line of raised surface into the soft 

 metal, giving a picture in intaglio, from which any 

 number of copies may be printed. 



The operation of printing from the intaglio is 

 very simple. The press consists of a shallow box, 

 with a hinged lid of plate-glass, and a bottom of 

 the same material. The mould is laid, face up, on 

 the glass bottom, and has poured on its centre a 

 small pool of a suitable ink, composed of gelatine, 

 carbon, and colouring-matter. The paper is laid 

 on this, and the lid pressed down firmly. This 

 causes the ink to spread out between the mould 

 and the paper, filling up the cavities in the former, 

 and forcing the superfluous portion over the edges. 



Although photographs can be successfully trans- 

 ferred to wood-blocks for the use of the engraver, 

 the process has not received the attention which 

 it deserves. There are several methods by which 

 it can be accomplished ; the following, from its 

 having stood the test of extensive practice, may 

 be described. The surface of the block is pre- 

 pared with Chinese white and enamel, as already 

 described (p. 771), with this difference, that the 

 enamel must preponderate, and the whole ground 

 be a little thicker than for ordinary purposes. It 

 is then coated with a solution of i ounce of albu- 

 men in 16 ounces of water. When dry, another 

 coating is applied of i ounce albumen, 4 ounces 

 water, 40 grains chloride of ammonium ; when 

 thoroughly dry, it is sensitised with ether, i ounce ; 

 alcohol, i ounce ; gun-cotton, 8 grains ; nitrate of 

 silver, 30 grains. On this surface, the subject may 

 then be printed from the negative in the usual 

 way, after which the collodion must be thoroughly 

 dissolved off with ether and alcohol in equal 

 quantities. It is then fixed with hyposulphite of 

 soda for a few minutes, and washed with water. 

 When dry, it is ready for the engraver. 



We may add that figs, n, 12, and 14 in the 

 present article, and the figure of the Walter print- 

 ing-press at the head of the preceding sheet, were 

 photographed on the wood in this manner. 



In working the ordinary collodion process, 

 technically called ' ivet collodion,' it is necessary 

 to expose the plate within a short time after its 

 removal from the bath ; and in consequence, when 

 taking landscape negatives, the operator is bur- 

 dened with much troublesome material, including 

 a tent in which to work. This inconvenience 

 led to the discovery of a method by which the 

 sensitive plates might be made so as to keep good 

 for a period long enough to enable the photog- 

 rapher to prepare a supply before starting on a 

 tour, and to develop them on his return. This , 

 ' dry collodion' process consists essentially in 

 thoroughly washing the plate on its removal from 

 the bath, and then immersing it in a solution of 

 certain organic substances, and afterwards drying 

 it. Various modifications of the process have 

 from time to time been recommended, each gener- | 

 ally taking the name of the organic matter which ' 

 was used as a preservative ; such as the ' collodio- 



784 



albumen,' the ' albumen,' ' tannin,' ' honey,' ' coffee/ 

 ' malt,' &c. We may take as a type the ' Beer and 

 Albumen' process, introduced by Mr Davies of 

 Edinburgh, in 1867, a modification of which was 

 used by Captain Abney in photographing the 

 transit of Venus in December 1874. On re- 

 moval from the sensitising bath, the plate is 

 washed in three changes of water, and then placed 

 in a flat dish of a preservative solution, made as 

 follows : Strong sweet ale, 10 ounces, the albumen 

 of one egg, and 10 grains of pyrogallic acid. 

 Those are put into a bottle capable of holding 

 20 ounces, and thoroughly shaken. After stand- 

 ing for a short time, it is filtered, and is then 

 ready for use. The plate should be left in the 

 preservative for two or three minutes, and may 

 then be set upon end, to dry spontaneously, or be 

 dried by artificial heat. In this state, it is ready 

 for exposure, and will keep indefinitely. The 

 exposure required is much longer, probably six 

 times, than for wet collodion ; but as considerable 

 latitude is allowable, it is better to over than under 

 expose. For the development of the image, the 

 plate is first washed under a tap, till the water 

 flows evenly across the surface, and then has 

 poured over it a solution of pyrogallic acid, four 

 grains to the ounce of water. After this has been 

 poured off and on several times, one or two drops 

 of a weak solution of ammonia a drachm of 

 ' stronger solution of ammonia ' to an ounce of 

 water are added, and the image should immedi- 

 ately appear. The solution must be kept in con- 

 stant motion until the general detail of the picture 

 is fairly visible, then washed off under a tap. 

 Although the image at this stage may be fully 

 out, when examined by reflected light, it will be 

 found, on looking through the negative, to be 

 much too thin, or weak, for printing purposes, and 

 must be strengthened with pyrogallic acid and 

 silver, as recommended for the intensification of 

 the wet collodion film. 



A method of preparing dry plates, different in 

 principle from the above type, was introduced 

 by Messrs Syce and Bolton of Liverpool. It 

 is known as the ' Collo-bromide ' or 'Emulsion' 

 process, and its peculiarity consists in coating the 

 plates with a sensitised emulsion, thereby getting 

 rid of the costly nitrate bath, and doing, by one 

 operation, what, in all previous methods, required 

 two. In consequence of this, and the facility 

 with which the plates may be prepared, the pro- 

 cess is at present extensively and successfully 

 practised. A bromised collodion is made by dis- 

 solving pyroxyline, 6 grains ; cadmium bromide, 

 6 grains ; and ammonium bromide, 3 grains, 

 in a mixture of 6 drachms of sulphuric ether, 

 and 2 drachms of alcohol. A tolerably large quan- 

 tity of this should be made, as it will keep in- 

 definitely, and improve by age. The sensitive 

 emulsion is made by adding to each ounce of the 

 collodion 12 grains nitrate of silver, dissolved in 

 2 drachms of alcohol, and the plates are coated 

 in the manner already described. They are 

 then 'plunged into a dish of water, and washed 

 till it runs smoothly over the surface ; after which 

 they are immersed for a minute or two in a solu- 

 tion of tannin, or other preservative, and then 

 dried. The image is developed with pyrogallic 

 acid and ammonia, to which are added a few drops 

 of a solution of potassium bromide, to somewhat 

 restrain the action. 



