June 9. 1855.] 



NOTES AND QUERIES. 



451 



PHOTOGKAPHIC CORRESPONDENCE. 



On the Alteration of Positives, and their Revival. — After 

 the reading: of the paper by MM. Davanne and Girard 

 before the Societe Frangaise de la Photographie, which we 

 published in our last Number, a discussion ensued, in which 

 M. Humbert de Molard stated that he feared that the 

 process of MM. Davanne and Girard, though incontest- 

 ably good in other respects, could not be used except at a 

 price rather extravagant for photography. 



M. Girard pointed out that the bath of gold will serve 

 for a great many photographs before it is sensibly ex- 

 hausted, and that the price for reviving each image is 

 very small. 



M. de Molard said that he had for a long time occupied 

 himself with the stability, coloration, and restoration of 

 the images, whether negatives or positives, by the aid of 

 a solution of cyanide of potassium, saturated with iodine, 

 as might be seen in a pamphlet of C. Chevalier, published 

 in 1847j p. 140. The process demands care and patience, 

 but when well executed gives good results : 



Distilled water - - - 10 grammes. 



Cyanide of potassium - - - 1 „ 



Crystallised iodine, about - - 3 „ 



The iodine must be added, only in proportion as it dis- 

 solves, until complete saturation, that is to say, until the 

 aqueous solution of cyanide of potassium, at first white, 

 turns to a violet colour by excess of iodine ; a few drops 

 of the cyanide are then cautiously added, until the violet 

 colour of the solution becomes of a greenish-white: 

 the object of this process is, to destroy the dissolving 

 energy of the cyanide, so as to prevent its attacking the 

 blacks of the picture, whilst the iodine is deposited by its 

 affinity for the silver, and, at the same time, to let it have 

 sufficient strength to prevent during the immersion the 

 small quantity of iodine, which attempts to do so, fixing 

 itself upon the whites. 



M. de Molard's process for reviving a print is as follows : 

 The print is immersed in a clean basin, containing about 

 200 grammes of common filtered water. After complete 

 saturation he raises it out with the left hand, and with the 

 right hand adds six, eight, or ten drops, not more, of the 

 solution of iodized cyanide ; he stirs it for a minute, and 

 then plunges the picture in again ; the tone immediately 

 changes, the shadows which have been red or brown 

 passing to black, blue, violet, &c. ; after washing with 

 common water the print is completely fixed. If the print 

 bas become yellow from a mismanagement in the fixing 

 by hyposulphite of soda, he proceeds as before ; but in 

 this case the colour still remains the same. Nevertheless 

 the yellow parts will have combined with a certain quan- 

 tity "of iodine to the exclusion of the whites, which are 

 defended by the cyanide of potassium, and there will be a 

 new layer of iodide of silver, more or less rich, capable of 

 being developed without any previous solarisation by the 

 ordinary weak alcohol gallic acid bath, to which a drop 

 of nitrate of silver iias been added. In order to obviate 

 the graj', dull, and slaty colour which these prints have, 

 they should, before this process, be left for several hours 

 in a new bath of hyposulphite of soda of ten per cent., to 

 which has been added a small quantity of the salt of gold 

 of Gelis and Fordos. 



M. Humbert de Molard then read the following paper 

 on the fixing of positive photographs : 



" The fixing of positives is without doubt one of the 

 questions which is interesting to most photographers ; are 

 they not in fact occupying themselves with it at the 

 present time ? If we look at the Comptes rendus de la 

 Societe d' Encouragement, we find, in all the reports made 

 on photography since its origin, the same complaints, the 



same regrets about the instability of positives ; and the 

 proof is, that, in the last programme given by the Soci6t6 

 d" Encouragement pour les progres de la photographie, it is 

 expressly stipulated that, to merit public approval, the 

 images ought to be at least as durable as water-colour 

 drawings. In a memoir, or collection of notes deposited 

 in 1850 with the Societe d' Encouragement, and apropos of 

 the before-mentioned programme, I gave then, as did many 

 others, all the information connected with my daguerreo- 

 type apparatus. Now, this of which I am going to speak 

 is already old, — I admit that this will be retrospective 

 photography ; but what does it signify, since, although, 

 five years have passed, the question is still so new that it 

 is being continually agitated." 



M. Humbert de Molard then read a paper of his, given 

 to the Societe d' Encouragement in 1851, in which he at- 

 tributed the failing of photographs in a great measure 

 to the use of hvposulphite of soda, and recommending 

 instead ammonia", diluted with five or six times its weight 

 of water, as the best solvent of chloride of silver. The 

 President remarked that hyposulphite of soda is, how- 

 ever, a much more energetic solvent than ammonia. 

 M. Humbert de Molard answered, that that was precisely 

 the reason why he deprecated the employment of it. The 

 hyposulphite dissolves the sub-chloride of silver as well 

 as that which is most solarised ; the ammonia, on the 

 contrary, does not attack it, and leaves untouched the 

 smallest miirks. 



M. Humbert de Molard, in continuation of his paper read 

 before the Societe d' Encouragement, said : " My theory 

 for taking positives has always consisted in not wishing 

 to obtain the tone of the images, as has hitherto been the 

 practice, by their more or less prolonged immersion in the 

 bath of hyposulphite, but to develope the colour wished 

 for afterwards by the employment of various metallic 

 chlorides, of which ammonia precipitates the colouring 

 principles. These effects are always light, almost invisible 

 at first, but soon increase by means of a second operation, 

 on which success depends. After the first washing in 

 ammonia (for a few minutes only), I proceed immedi- 

 ately to a second washing in ammoniure d'or (ammonio- 

 chlo'ride of gold, NH4 Cl+Au CI3+2HO .'). Whether 

 it be Fizeau's chloride of gold, Gelis and Fordos' salt of 

 gold, or solution of gold in aqua regia, neutralised by 

 chalk, does not signify ; the effect is always the same. The 

 sheet of wet paper should be laid at the bottom of a basin, 

 and about a "decilitre" of solution of gold (1 gram, to 

 500 of water) poured upon it. In a short time, and by con- 

 tinually agitating the basin, the gold deposit takes place 

 uniformly ; we observe the print, still ammoniacal from 

 the effect of the first washing, change in tone and pass 

 through the intermediate tints of Indian ink, sepia, &c. 

 At last, as soon as the image has arrived at the wished- 

 for tone, I proceed to fix it definitely by a solution of 

 iodized cyanide of potassium." M. Molard stated that he 

 had found that his positives had remained unaltered for 

 eight years. 



The President remarked that it was impossible to fix 

 positives and negatives in the same manner. M. H. de 

 Molard stated, " That certainly negatives would not be 

 fixed by ammonia, as ammonia will not dissolve iodide of 

 silver." Now ammonia and ammoniure d'or, of which I 

 have spoken, are only used in positives : as to fixing by 

 iodized cyanide of potassium, it probably might be applied 

 both to positives and negatives. He showed several 

 specimens, displaying the different effects which can be 

 obtained. M. Belloe stated that he willingly admitted 

 the superiority of the fixing by ammonia, because of its 

 volatility, and the great advantage of being able to finish 

 a great many photographs in a very short time. At the 

 same time, he was not exclusive enough to abandon the 



