A New Method of Colour Photography

Abstract

THE latest method of colour photography distinguished as the “Warner Powrie” process, and is well illustrated at the first exahibition of the Society of Colour Photographers, which will close on October 26. It will presumably be some little time before the plates are generally obtainable, but so far as can be from the examples shown and the details of their preparation, it is a process that will offer special advantages. Mr. Powerie has been working at the subject for many years, and has succeeded in producing a triple-coloured lined screen with better and finer has been possible by previous methods, and without either gap or overlap. He discards ruling in favour of a very ingenious method of printing that does away with all need for the troublesome registration that becomes almost impossible with fine lines. The glass is coated with a bichromated colloid, exposed under a black-lined screen that has spaces half the width of the lines, and developed in warm water. This leaves the colloid in lines with spaces of bare glass twice as wide as the lines. By immersion in a solution of a green dye the lines are stained, and by the application of formalin or chrome alum the colloid is made quite insoluble and the dye fixed. The plate is coated again, exposed under the same black-lined screen, the only precaution being that the green lines already made shall be covered with the black lines of the overlying screen. After exposure and development the plate is immersed in a solution of a red dye to stain the second set of lines, and again treated with a hardening agent. The plate is coated once more, and this time exposed alone with its back to the light, so that the red and green lines already made serve to protect the coating from light action. So after development all the remaining spaces are exactly filled with colloid, and this is then dyed blue. The prepared plate is coated with a suitable photographic emulsion, and can be used in a similar way to the “autochrome” plates of Messrs. Lumière, which we have already described. The chief difference between the two apparent by mere inspection is that the colours are in lines instead of as a random grain. But the lines can be made so fine that they are invisible to a normal eye without assistance.

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