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Subtractive Processes 635
conjunction with brilliant yellow for the red impression, it being claimed that the lighter tones were thus rendered yellow. The practice of the mixture of dyes to give this effect was common knowledge, and had been in use almost since the first subtractive pictures were made (see von Hiibl, p. 443).
A. R. Lawshe7 disclosed a method of cementing the celluloid base of two-color subtractive pictures so that the images would be on the outside. This patent is for a method of producing multi-colored pictures (see p. 334), and whilst it deals primarily with stills, its use for cinematography is specifically disclosed. This it is believed is the first instance of the pictures being cemented base to base.
A. Coppier73 would produce films in colors by making enlargements, coloring the same and then assembling and copying. M. Holfert74 patented the use of films which were each coated with the same positive emulsion. D. F. Comstock75 patented the control of the gammas, or degree of contrasts, of the positives, by alteration of the color of the printing light. This principle was first suggested by Lemann70 and had been in constant use for many years. W. Finnigan and R. A. Rodgers77 would take the negatives with two films in contact with one another. The front one being an ordinary emulsion, and the rear a panchromatic, sensitized with a mixture of pinacyanol, pinaverdol and fuchsin. The positive from the rear negative was dyed blue-green, and that from the front one stained a pink-red. The two were to be "hermetically fastened together in any way that may be desired."
C. Raleigh78 patented the reduction of the intensity of one colored image with regard to the other. H. Tappen79 would dye the celluloid with a dye, that would not wash out, for positive work. The Technicolor Motion Picture Corporation80 proposed to form subtractive films by cementing two thin films either face to face or back to back, with a temporary metal strip backing if desired. Or relief films on metal backings might be used for imbibition. Accurate registration was to be obtained by the perforations. A. P. Kennis81 would print on to triple-width film, suitably color the positives by a photomechanical process, then slit the wide strip, which carried six rows of perforations and join up the ends as usual. W. Zorn82 patented a process for the chemical treatment and coloring of films, in which the chemicals were brought into a pasty condition with a binding medium, and then applied to the film. T. A. Edison83 would take ordinary black and white negatives, make a positive therefrom and blockout the various colors, make a second negative from which the projecting positive was made. V. Casiraghi, L. Sabourin and Y. Sabourin84 patented the use of three films, exposed side by side through three lenses and cementing the constituent positives together.
1. E.P. 4.045, 1912; Brit. J. Phot. 1913, 61, 232.
Many of Thornton's patents for dichromate processes have but indirect connection with color. See E.P. 3.384; 3.385; 4,043; 4,044; 4,164; 12.231; 14,433;