# Popular Science Monthly/Volume 28/February 1886/The Problem of Photography in Color

Layout 4
* THE PROBLEM OF PHOTOGRAPHY IN COLOR.
By OGDEN N. ROOD.
PROFESSOR OF PHYSICS IN COLUMBIA COLLEGE.
MY attention was first called to this subject in 1853. At that time I was an assistant in the "Yale Analytical Laboratory," which afterward developed into the present Sheffield School. The interest of the Professor of Chemistry, John Porter, was excited by some articles on this subject which had recently appeared in France, and he was desirous of making experiments to test an idea that had occurred to himself. The sensitive surface was to be prepared while actually under the influence of colored light, so that from the start the colored rays should be able to act on it and influence the molecular condition of the newly formed combinations. A prismatic spectrum was to be employed, and it was hoped that the red rays would persuade the newly born silver salts to reflect red light and only red light, while the same salt, when generated under the influence of the green rays, by the aid of this early education was to be made capable hereafter of reflecting green light, but incapable of reflecting red, yellow, or blue light. Expressed in the language of the undulatory theory of light, the idea would be about as follows: expose molecules in act of formation to the long waves of red light, and ever after they will be capable of reflecting mainly the long waves of red light; all other kinds they will absorb and convert into heat.
This task having been assigned to me, I entered on it with zeal, and arranged a dark room; the solar spectrum was made to fall nicely on the table, and many of the processes known at that time were in succession tested. The photographs of the spectrum thus obtained were not at all uniform in color; sometimes they would be delicately shaded from a dull-red gray to a blue or violet-gray and often they presented minor changes of color variously disposed. Favorable indications were followed up as they presented themselves; but after a lime I became convinced that the play of color in the photographs was solely due to the greater or less energetic action of the light upon the sensitive substance, and that exactly the same results could be obtained by using white light, more or loss intense. When the work was finished, I presented my written report with the photographs, and the professor, after studying it, came to the same conclusion. The "nascent" idea was not feasible.
And yet photographs in color of colored objects have been obtained. Upon one occasion, about twenty-five years ago, I obtained a very fine one. The subject was a large elm-tree and a rod farm-house, these two objects filling up almost the whole plate. The ordinary wet-collodion process was employed; the negative, after being ​removed from the hypo, was washed and dried as usual; but, when I examined it by reflected light, it turned out that the green tree was colored dark green just as nicely as if it bad been a camera image, and the red house was not a bit behindhand in truth and delicacy of hue. A photograph in colors, sure enough! But an examination with a lens, and a little turning and twisting of the plate, caused the illusion to vanish: the colors were those of "thin plates," soap-bubble colors, caused by the interference of light. Wet collodion often shows them in patches when it is somewhat rotten, and this sample was very rotten. The interference effect had nothing to do with the color of the light, but was controlled by its intensity. Once I bad a chance to examine some photographs in color of gayly dressed dolls made by Niepce de Saint Victor, and it seemed to me that the pale colors they presented were produced by a species of interference, acting by means of the presence of more or less finely divided particles. The details of my examination I do not recollect, but merely the conclusion that the appearances presented were due to causes analogous to those that were effective in the case of my glass negative. Photographs in color, such as they are, can be obtained with sufficient patience; but, in order to give this fact the slightest value, it is necessary to prove that a corresponding amount of patience would not be rewarded by the production of colored photographs of objects which were gray, light gray, dark gray, etc. When we think we have made a discovery, our first duty is to destroy it mercilessly if possible, and the reproduction of the same effects with white or gray objects is the proper mode of administering justice in this case. It is barely possible that some one may ask why a process that renders the colors correctly is a failure merely because corresponding colors can be obtained when the natural objects are tinted gray. The question answers itself; white and gray objects will be colored in the photograph, and, worse than that, the same color in the natural object will vary in the photograph with its brightness or luminosity.
Let us now examine this subject from a theoretical point of view, and ask ourselves why we should hope that photographs in color could ever be produced. We see the rich red rays of the spectrum falling on the plate, and we imagine that a substance which is sensitive to light will somehow be acted on by them, and arrange itself so that ever afterward it will better be able to reflect red light than any other kind of light. Why? Why should a substance that has been acted on by long waves be better able to reflect long waves than those that are shorter? Why should a sea-beach that has been acted on by long waves be on that account better able to reflect and redirect to the ocean long waves rather than mere ripples? The waves of light produce in sensitive substances chemical changes; new compounds are formed; why should the long waves of red light produce compounds that are especially capable of reflecting long waves, or red light? ​When we undertake to make a photograph in color, in effect we ask one and the same chemical substance to reflect for us long, medium, or short waves, red, green, or blue light, according as it has been acted on by waves of greater or lesser length. The demand seems to me preposterous.
The hope for photography in color lies in a different and less independent direction. By the use of suitably colored plates of glass placed before the lens of the photographic camera, it is possible to obtain ordinary negatives of the red, yellow, and blue constituents of a brightly colored surface—a carpet, for example. These can be made to yield red, yellow, and blue positives by the aid of the photo-lithographic process; and when these three positive impressions are superimposed on the same sheet of paper, a more or less successful reproduction of the colored object is obtained. The selection of the three transparent pigments used in printing is necessarily left to the taste and judgment of the operator, or I should say artist, as without considerable artistic knowledge the results are not likely to be valuable. It will be seen, then, that in this process photography is really made to act as an aid to chromo-lithography, and the results are really chromo-lithographs, the work being mainly performed by the camera and colored glasses. I do not see why it should not be possible in this way to reproduce more or less successful colored pictures of brightly tinted objects.
When we come to landscape the problem is more difficult, for a large part of its color consists of delicately tinted grays, the handling of which would be, to say the least, very troublesome, and would require far more than the superposition of the three layers of pigment just mentioned. For progress in this direction it would be necessary that the experimenter should, at the same time, be a skillful photographer, a good chromo-lithographer, and a landscape-painter. The results obtained would not be exact representations of natural scenery, but rather sketches in which the artistic taste presided over, modified, and massed together natural tints. They would be none the worse for that. Of course, there would still remain the difficulties connected with an artistic disposition of light and shade, and the still more insuperable ones of composition; for the disposition of objects in a landscape is rarely just what we want, or even what we are willing to tolerate. On the other hand, there are many simpler objects where this process would probably succeed very well, such as colored designs of all kinds of decorated objects, and all those cases where the coloring is simple and not too evanescent.—Photographic Bulletin.