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258 THE PHOTOGRAPHIC NEWS. [May 29, 1868. This mixture is dissolved in a porcelain dish on a hot- water bath, and then is added :— Bichromate of ammonia... 1} grammes The whole is agitated for several minutes, in order to bring about perfect dissolution and mixture of the bichromate. A glass plate, such as is used for obtaining gelatine moulds, is rubbed over lighty with a little ox-gall ; if is then coated with the sensitive mixture by passing it over a very fine wire sieve covered with a piece of fine cambric, the superfluous material being poured off and the plate allowed to dry horizontally. Five or six hours are required to dry the film when placed in a room heated to 20 degrees Cent. When dry, the plate is coated in the ordinary manner with thin normal collodion, and, five or ten minutes after wards, when this has set perfectly hard, a second coating of thick collodion, made up according to the following formula, is placed upon it:— Ether ... ... 100 grammes Alcohol 100 ,. Gun-cotton 2 to 6 „ Castor oil 4 „ The castor oil is an indispensable constituent of this collodion, for upon it depends the whole value of the process. It imparts suppleness and strength to the collodion, and prevents the latter from becoming shrivelled. From some cause or other, for which no chemical reason can be assigned, it is found that if the castor oil penetrates into the sensitive material, the employment of repeated applications of boiling water is necessary for washing and developing the picture. It is on this account that a thin film of col lodion unmixed with castor oil is first applied as a preser vative to the sensitive material. To avoid the employment of two films of collodion, the coating of thick castor oil collodion may first be applied and allowed to dry, and then the sensitive mixture superposed ; in this case no fear need be entertained of the castor oil doing any harm, but great care must be taken to employ glass plates of the most even and uniform description, placed upon a perfectly level surface, so that the film'of collodion is of the same thickness throughout. An irregular coating of collodion will militate against the perfect removal of the film, which refuses to leave the plate in those parts where the material has been insufficiently applied. Either of these methods may be followed, according to the description of pictures that are desired. The first is applicable to the production of prints required on a thin film destined to be mounted upon cardboard or upon glass, or of dull unglazed pictures, in which case the film of col lodion is dissolved away, in order to remove the brilliant surface. This is best done by mounting the print, when it is thoroughly dry, upon cardboard or glass, and dipping it into a solution containing alcohol and ether in equal pro portions. The pellicle of collodion is dissolved, and the print remains adherent to the cardboard or glass ; the opera tion must, however, be closely watched, in order that the print is removed as soon as the collodion disappears, as a prolonged sojourn of the photographic image in the alcohol and ether has the effect of detaching the picture from its support. The ether and alcohol in which the collodion has been re-dissolved may be subsequently used for the manu facture of collodion by adding thereto a certain quantity of gun-cotton. The second mode of operating is useful for obtaining prints upon a thick film of collodion, which are to be used unmounted without any support, and for preparing fabric for photographic purposes. The fabric is prepared as follows :—A piece of fine linen or cotton cambric is mois- toned with alcohol, stretched upon a glass plate, and pressed by means of a roller, to expel the air-bubbles. When it has been well pressed against the glass, it is covered with a film of castor oil collodion, and allowed to dry. The sensi tive carbon mixture is next applied, and, when this is per fectly dcssicated, the whole is removed from the glass plate.* This prepared fabric is very suitable for photo-paintings and for enlargements; for the latter purpose photographers will find it especially applicable, as being very economical in its employment, and successful and permanent in its results. It has been stated that the carbon process is less costly than the ordinary silver process. This statement is easily proved by giving the cost price of the sheets of collodion- cuir and prepared fabric as manufactured and sold at the author’s establishment. A sheet of prepared carbon paper ready for manipulation in the pressure frame or upon the screen for enlargements, which is sold for rather more than three shillings, costs from one shilling to fifteen pence to prepare, according to the thickness of the collodion film. But to proceed with the process. As soon as the sensi tive film has been prepared, as has been described, upon a thin transparent pellicle, the sheet is placed under the nega tive, taking care that the collodionized surface is put in contact with the cliche. After a sufficient exposure, which varies according to the intensity of the light, but which is always much less than that required in the ordinary silver process, the print is placed in a bath of warm water in a dark room, and afterwards dried and mounted. One of the principal features of the process is the possi bility of imparting to the collodion-cuir, if necessary, the dull opaque appearance of ground glass, by means of which the necessity of backing is dispensed with in stereoscopic slides and pictures of that description. The specimens ex hibited by the author sufficiently showed the value of this modification. The unglazed surface of the film allows of painting and retouching of every description, and no glass mounting being required for transparent photographs, their weight and expense are much diminished. The author accompanied his remarks by a practical de monstration of the process. He applied the sensitive material to the surface of a plate; detached another film prepared some time beforehand, and developed in warm water three prints, of which two were stereoscopic on dull collodion, and the third a large transparency. The experiments were ex ceedingly successful, and were watched with great interest. ON THE PRESERVATION OF COLLODIONIZED PLATES IN A MOIST CONDITION. BY GENERAL MONOIN.f At the special request of a member of the Society, I have much pleasure in communicating the details of a method, recently employed by myself, of working with wet plates which had been preserved and exposed to the vicissitudes of travelling in a grooved box constructed for the purpose. The process (if process it can be called) is based upon the fact that if a plate coated with collodion in a certain manner, which I will hereafter indicate, be carefully washed after its exit from the sensitizing bath, and afterwards placed in a bath of pure water sheltered from the light, the collodion will remain perfectly adherent to the glass, provided the water surrounding it is not violently disturbed ; moreover, the prepared plates lose but very little of their sensitiveness in this condition. In making this statement I must frankly admit that I cannot speak for certainty of a longer period than ten days, as I have myself never kept plates for a longer time ; the only thing to be observed in working the process is to add to the developer a few drops of nitrate of silver solution to replace that removed in the operation of washing. The Collodion and Silver Bath. First of all it is necessary for me to state that when speak ing of the employment of water, I always mean rain-water; * We are at a loss to understand how the linen prepared in this manner is to be printed, as the treatment with alcohol would scarcely render the fabric transparent.— ED P. N. t Read before the French Photographic Society.