Dec. 1. 1855.] 



NOTES AND QUERIES. 



437 



not found that any method of printing which has been 

 commonly followed, will necessarily produce fading pic- 

 tures, if certain precautions be adopted, nor have they 

 evidence that any method which has been adopted, will 

 not produce fading pictures unless such precautions are 

 taken. 



Causes of Fading. — The most common cause of fading 

 has been the presence of hyposulphite of soda, left in the 

 paper from imperfect washing after fixing. The Com- 

 mittee think it right to state, that they have been unable 

 to find any test to be relied upon, which can be used to 

 detect a minute portion of hyposulphite of soda, in the 

 presence of the other substances which are obtained by 

 boiling photographs in distilled water and evaporating to 

 dryness; yet they have no doubt of the truth of tlie 

 above statement, from the history given of the mode of 

 Avashing adopted. The continued action of sulphuretted 

 hydrogen and water will rapidly destroy every kind of 

 photograph; and as there are traces of this gas at all 

 times present in the atmosphere, and occasionally in a 

 London atmosphere very evident traces, it appears rea- 

 sonable to suppose that what is effected rapidly in the 

 laboratory with a strong solution of the gas, will take 

 place also slowly but surely in the presence of moisture, 

 by the action of the very minute portion in the atmo- 

 sphere. The Committee find that there is no known 

 method of producing pictures which will remain unaltered 

 under the continued action of moisture and the atmosphere 

 in London. They find that pictures may be exposed to 

 dry sulphuretted hydrogen gas for some time with com- 

 paratively little alteration, and that pictures in the 

 coloration of which gold has been used, are acted upon 

 by the gas, whether dry or in solution, less rapidly 

 than any others. They also find that some pictures 

 which have remained unaltered for years, kept in dry 

 places, have rapidly faded when exposed to a moist at- 

 mosphere. Hence it appears that the most ordinary cause 

 of fading may be traced to the presence of sulphur, the 

 source of which may be intrinsic from hyposulphite left 

 in the print, or extrinsic from the atmosphere, and in 

 either case the action is much more rapid in the presence 

 of moisture. 



Mode of Mounting Photographs. — The Committee find 

 that taking equal weights, dried at a temperature of 212'-', 

 of the three substances most frequently used, viz. gelatine, 

 gum, and paste, the latter attracts nearlj- twice as much 

 moisture as either of the former ; and as in practice a much 

 smaller weight of gelatine is used than of gum, gelatine 

 appears to be the best medium of these three ; and the 

 Committee have evidence of fading having in some 

 cases been produced by the use of paste. In illustration 

 of some of the circumstances alluded to above, the Com- 

 mittee think it well to mention some instances of prints at 

 present in their possession. Out of several prepared to- 

 gether in 1844, three only are unaltered and these were var- 

 nished soon after their preparation with copal varnish. 

 Half of another print of the same date was varnished, and 

 the other half left ; the unvarnished half has faded, the 

 varnished remains unaltered. Three pictures were pre- 

 pared in 1846, all at the same time, with the same treat- 

 ment; when finished, one was kept unmounted; the 

 other two were mounted with flour-paste at the same 

 time, one of these latter having been first coated with 

 Canada balsam ; at present the unmounted one and the 

 one protected with the balsam are unchanged, whereas 

 the other has faded. A picture prepared in 1846 was so 

 exposed that the lower part of it became wetted with 

 rain ; at present the part so wetted has faded, while the 

 rest of it remains unaltered. Several pictures were pre- 

 pared and mounted about ten years ago, and kept in a 

 dry room for about three years without any change, after 



No. 318.] 



which they were placed in a very damp situation, and 

 then faded decidedly in a few months. The Committee 

 propose very shortly to actually test the durability of the 

 various modes of printing, by exposing pictures to dif- 

 ferent treatment, and they have been fortunate enough to 

 obtain a grant of space for this purpose from the Crystal 

 Palace Company. The Committee make the following 



suggestions, arising out of the above Report: 1. That 



the greatest care should be bestowed upon the washing of 

 the prints after the use of hyposulphite of soda, and for 

 this purpose hot water is very much better than cold. 

 2. The majority of the Committee think that gold, in 

 some form, should be used in the preparation of pictures, 

 although every variety of tint may be obtained without 

 it.* 3. That photographs be kept dry. 4. That trials 

 be made of substances likely to protect the prints from 

 air and moisture, such as caoutchouc, gutta percha, wax, 

 and the different varnishes. 



Philip H. Delamotte. 



Hugh W. Diamond. 



T. Frederick Hardwicii. 



T. A. Malone. 



John Percy. 



Henry Pollock. 



Geo. Shad bolt. 



" On a New Method (f preserving Collodion Plates 

 Sensitive," by Charles A. Long. — The important position 

 now occupied by the photographic art, and the influence 

 it seems likelj' to exercise on the progress of science 

 generally, leads me to hope that the process I am about 

 to describe may be deemed worthy a passing notice in 

 your valuable Journal. 



The collodion process, generally, is too well known to 

 need any detailed description, and I purpose therefore to 

 confine my remarks exclusively to the improvement in 

 the process, having reference to the capability of the col- 

 lodion film — after having been rendered sensitive — to 

 preserve its sensitiveness for an indefinite period ; so that 

 the operator may be enabled to prepare any number of 

 plates in his laboratory, and, as occasion offers, or favour- 

 able opportunities occur, he may expose his prepared 

 plates to the action of the light in the camera, and de- 

 velope the image impressed upon them at his leisure on 

 his return from the scene of operations. 



In order to render this description more clear, and the 

 point at which the improvement or novelty commences 

 more clearly defined, it may be as well to lay down the 

 principal features of the collodion process. 



The iodized collodion is poured upon a plate of per- 

 fectly clean glass, the superfluous quantity being returned 

 to the bottle; the plate thus collodionized is immersed 

 in a bath of nitrate of silver, the action of which is to 

 convert the iodide in the collodion into iodide of silver, or, 

 more properly speaking, into the sub-iodide of that metaL 

 The film of iodide, thus formed, is extremely sensitive to 

 light ; and on exposure, under proper circumstances, re- 

 ceives an impress from that influence, which has the 

 effect of commencing a decomposition which is carried on 

 to the required point by the developing agent employed — 

 usually pyrogallic acid. The image is then fixed by the 

 removal of any remaining sensitive substance, and a 

 negative proof is the result. 



In the process above described, it is necessary to 

 use the plate, or rather to expose it in the camera, and 

 develope the latent image before the film becomes dry ; 

 thus placing an insuperable barrier to the use of the co - 

 lodion process for taking views, &c., at a distance from 



* Dr. Percy and Mr. Malone consider that there is 

 not sufficient evidence in favour of gold, to warrant this 

 recommendation of its general use. 



