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Sub tractive Processes 633
ing, but would use eosin red. which was said to he mordanted by the chromium compound of the image. Or a black and white positive might be used instead of the second negative and a dye, such as fast red, which takes on the unexposed gelatin, or the second image might be obtained by an imbibition process. C. F. Jones'" patented the use of two separate negatives, toning one blue, then sensitizing with dichromate solution containing a yellow dye and printing the second positive on to this film and staining up in the appropriate color.
It must not be supposed that in this sketch of the subtractive processes all are included here that can be rightly considered so ; but only those not dealt with elsewhere, which will be found under various headings. For instance, many of the relief processes have been, or can be used, and various mordanting processes fall into the same category. Here, however, are grouped methods which it would seem could be best dealt with under this heading, the main idea of the patentees being to claim or produce subtractive cinematographic pictures.
W. V. D. Kelley37 would tone the first image by the diachrome process to a green, then sensitize with dichromate and print from the positive of the second record and dye with a pinatype dye. H. Shorrocks58 would adopt resists to protect one series of colored positives, and the others might be treated by the diachrome process, and after removal of the resist, immersed in a combined green and red toning mixture, consisting of ferricyanide, vanadium chloride and a ferric salt with ammonium chloride, sodium citrate and rhodamin. The iodized image absorbed the dye, while the hitherto protected images were toned green. S. M. Procoudin-Gorsky39 proposed to obtain a negative with recurring sets of color records, then to print the minus-yellow constituents first, iodize and dye with auramin, which was mordanted with aluminum acetate and then fixed. The film was again coated with emulsion, exposed under the minus-red negative, again iodized and dyed with rhodamin, again recoated and the final image toned blue with a cyanotype mixture.
Cemented Films. — E. Witte60 pointed out that with the additive process, special projection apparatus was required, and to obviate this he proposed to use multiple-film negative stock, which must be separable, and one carrier of which at least might be colored. Probably a species of film pack is meant. Subsequent registration was to be obtained by marks or perforations. The positives might be obtained by the carbon process, or by the conversion of the silver image into a colored one. The inventor then says : "After making the negative films they are brought together with the similarly or like prepared positive films, and these two films provided with corresponding letters or marks. Now the possibility is given without further trouble of bringing the separate positive bands into corresponding contact, and to convert them in a known manner into one colored image (possibly orange and blue), if a printing process has not been