Colors in their Relation to Artificial light.

The Scientific America 23, 1.12.1866

Never select colors in the evening, is an old maxim, whose value can be attested by many a disappointed purchaser, who, ignorant or disregarding this advice, and deeming himself the favored possessor of some tint of rare excellence, discovers on the return of daylight a color far from equalling his anticipations. The artist, overtaken by darkness, hastens to apply the last touches to some masterpiece, but the morning light reveals how poorly his intentions have been realized. The cause of this inconstancy is explained,a nd a remedy suggested, in a late article in the Photographic News.

From the spectral analysis, we learn that the flames of our lamps or gas lights contain sodium, which, in burning, yields a yellow flame, as strontium gives a red, and iridium a blue flame. Now when the color blue illuminated by the yellow light it appears green, but if the flame strikes a color complementary to yellow it will appear white or black, according as the body has, or has not, the power of reflection; which is equivalent to saying that this flame alters the nature of colors, deepening the hues of some and extinguishing others.

Take a spirit lamp and put into it a piece of common salt, the wick will soon become saturated with sodium in solution, the flame, in consequence, will be yellow, and all colors will assume a monotonous white, black, or gray. It is only when this substance is in excess that we have the total extinction of colors, but a flame loss rich will produce a partial extinction, and this is the reason why colors are at all visible by gas light. It may be asked, where does illuminating gas derive this sodium? From the coal, from the water with which the gas was washed; it comes also from the matters employed in its purification, and probably even from the atmosphere.

The only hues which resist only slightly the yellow flame, are furnished by the blue; all the other colors are profoundly modified. Fortunately the flames which serve as sources of light are never saturated with sodium, hence the effects are greatly modified.

The light from the burning of magnesium alone brings out the various colors, both natural and artificial, the same hues as they appear by day light. The services of chemistry render, then, to painting not only colors more or less rich, but also it has endowed it with a mode of lightning whereby the painter may be able to work at night without incurring mistakes or illusions.

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