The operation is nearly as rapid as that of making an ordinary tintype. The finished pic ture is termed an since its color ing is automatically obtained.
The method is the most impor tant, as it has the greatest commercial possi bilities, and gives the most varied and most sat isfactory results. Although Callen, in 1865, was probably the first to suggest the method, and du Haroun, in 1869, outlined it clearly, they and those that followed them were on the wrong track, working on the theory of Brewster, which never could lead to success, instead of that of Young, Helmholtz and Maxwell, now univer sally accepted. The first to recognize this was Fred E. Ives of Philadelphia, and to him more than to any other, or indeed to all the others together, are we indebted for the great progress that has already been made. The first experi mental half-tone three-color plates and prints were made in 1881.
In 1910 Mr. Ives introduced an improved system of color photography by which dupli cate color photographs on a transparent film were obtained. In a specially constructed camera three sensitized dry plates, two of which were sensitive to red and green rays of light and one to blue rays, were exposed simultaneously, after passing through the single camera lens, between which and the plates was interposed a yellow-orange trans parent light filter or screen for the purpose of reducing the strength of the blue rays.
The three sensitive plates were enclosed in a single plate holder, specially designed, so arranged that two of the plates were placed film sides in contact and a third, a trifle smaller in size, with the film side against the glass side of one of the two plates in film contact. The three plates were secured together at one edge by a flexible paper hinge and the whole was named a utripack.a To make an exposure in the camera (after focusing) the holder (containing the three plates) is inserted like an ordinary plate holder in the usual way. On withdrawing the plate holder slide, the smaller plate in the holder falls out by gravity and rests on the bottom of the camera in a horizontal position, but the other two plates are held in the holder in a vertical position. After this operation a second
yellow tinted transparent plate on the interior of the camera was dropped by a lever on the exterior, downward from the roof of the camera in front of the tripack plate holder at an angle of 45 degrees, the top of the plate being nearer the lens than the bottom, and formed a transparent reflec tion since its location was over the smaller sensitive plate lying on the bottom interior of the camera. Part of the light from the colored object, after passing through the camera lens and the yellow absorption filter, is reflected downward by the transparent reflector upon the two horizontal blue sensitive plates, while the rest of the light continues on in a horizontal direction, striking the underside first of the red sensitive plate film, passing through the same and acting upon the face of the yellow-green sensitive plate film in contact therewith. Thus three plates are in focus and exposed at one time. After exposure the angular filter screen plate is carried back to the camera roof, a lever on the outside raises the horizontal smaller plate into the plate holder till the plate holder slide is pushed in. The three exposed plates are each marked to indicate their respective color sensitiveness and are then developed as a unit in a tank developer for a specified time. Each image is distinct and sharp and exactly the same size. The duplicate positives are made from the three negatives upon a transparent film sensitized with a gelatine bichromated solu tion, printed in a printing frame in sunlight all three at one time, fixed in warm water. Where the light has acted, renders film absorbent to color. Each respective film picture is next dipped in its blue, red and yellow dye solution, washed, and when dry are clamped together so that images perfectly match between two pieces of glass, with the result that a beautifully brilliant colored very transparent picture, true to nature, is obtained. See Count PlicrrociiAPRY.