The process of A.C.A. Thiebaut is as follows: the paper has the following advantages:
First. The sensitive coating is regular, and its thickness is uniform throughout the entire surface of each sheet.
Second. It can be exposed for a luminous impression in any kind of slide as usually constructed.
Third. It can be developed and fixed as easily as a negative on glass.
Fourth. The negative obtained dries quite flat on blotting paper.
Fifth. The film which constitutes the negative can be detached or peeled from its support or backing easily and readily by the hand, without the assistance of any dissolving or other agent. Thus this invention does away with all sensitive preparations on glass, which latter is both a brittle and relatively heavy material, thus diminishing the bulk and weight of amateur and scientific photographers' luggage when traveling; it produces photographic negatives as fine and as transparent as those on glass, in so much that the film does not contain any grain; and, lastly, it admits of printing from either face of the film, as regards the production of positives on paper or other material, as well as plates for phototypy and photo-engraving, which latter processes require a negative to be reversed.
For the manufacture of my sensitized film paper:
First. A gelatinized sheet of paper is properly damped with cold water, and when evenly saturated it is placed on a glass, to which it is attached by means of bands of paper pasted partially on the glass, and partially on the edges of the said sheet; in this state it is allowed to dry, whereby it is stretched quite flat.
Secondly. I coat the dry sheet with a solution of ordinary collodion, containing from one to two per cent. cubic measure of azotic cotton (1½ per cent. gives very good results) and from 1½ to 2½ per cent. of castor oil (2 per cent. gives very good results); this coating is allowed to dry; and,
Thirdly. The glass, with the prepared paper upward, is leveled, and then it is coated, in a room from which all rays but red rays of light are excluded, with a tepid emulsion of bromide of silver to the extent of about one millimeter thick, and after leaving it in this position until the gelatine has set (say) about five minutes, with the film paper still attached, it is placed upright in a drying-room, where it should remain about twelve hours exposed to a temperature of from 62 to 66 degrees Fahrenheit; and,
Fourthly. The film paper is detached from the glass ready for exposure, development, and fixing in the usual manner. For the purpose of developing, oxalate of iron or pyrogallic acid answers equally well; for the purpose of fixing, I have found that a mixture by weight, water, 1,000, hyposulphite of soda 150, and powdered alum 60, produces excellent results, after being allowed to dry.
Fifthly. The film is peeled off the paper by hand, and can be immediately used for producing negatives recto or verso as above mentioned.
I claim as my invention:
First. The preparation or formation of gelatino-bromide film paper for photographic negatives, in the manner and for the purposes above described; and,
Secondly. The use for this purpose of castor oil, or any other analogous oil, more especially with the view of peeling off the film from the paper backing as above described.