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640 History of Three-Color Photography
be coated on both sides with sensitive material, and that the paper should be yellow or dark or non-actinic to prevent the light from one side penetrating through to the other.
Another interesting patent is one granted to the Societe des Etablissements Gaumont,4 which whilst not for color photography, utilized doublecoated film, and has some features valuable from the patent standpoint. The aim of the patent was the application of the anaglyphic principle to stereocinematography by the aid of a single film, printed on both sides in different colors. The film was to be coated on both sides with gelatin emulsion with a substratum or underlying film of an actinically opaque color. Or it might be coated with dichromated colloid on both sides. The images were to be obtained in complementary colors, red and green being cited in the patent. The positive was to be observed through colored glasses, thus giving the effect of relief, the principle being that of d'Almeida and du Hauron.
J. E. Thornton5 followed Gaumont's method in a very striking manner, and the similarity between the two in the use of the "opaque or lightobstructing medium" between the sensitized layers is remarkable. It will be understood that "opaque" here means actinically opaque to the printing light, and not opaque like metal. The same inventor6 again patented the same idea, but this time admitted the possibility of using a single negative film with recurring color records, instead of the two separate negatives of the previous patent. In a further patent7 he proposed to make from an alternating color record, two or more separate negatives and to print them on double-coated positive film.
A. Hernandez-Mejia* also patented the use of double-coated film, and his first claim reads : "The improved process of making a colored photographic transparency, for projecting or viewing by direct or reflected light, which consists in simultaneously taking two negatives of the same subject, from the same view point, respectively through screens of complementary colors, one of said negatives being directionally reversed with respect to the other. Printing from one of said negatives upon one side of a single transparent positive film, sensitized on both sides, and from the other of said negatives upon the opposite side of said positive film, with the images in register, treating one side of the positive so that the image thereon will appear in one color, and treating the opposite side of said positive so that the corresponding image will appear in a complementary color." Under the name of "Colorgraph," this process was described by Hernandez-Mejia9 and he stated at the end of his article: "The double-coated positive stock has arrived from Germany, so that the feasibility of this double coating is now commercially established."
W. F. Fox10 assigned to the Natural Color Pictures Co., the use of double-coated pictures, which were produced by treating both sides with a mixture of uranium nitrate, f erricyanide and acid, then fixing. The film