About “sulfur solutions” of all colors of the spectrum. (On the question of the reason for the coloring of ultramarines)

Abstract

It has long been noticed, during certain physical and chemical processes with substances containing sulfur, the appearance of violet, indigo-blue, blue and green colors, sometimes remarkable in their beauty. These color reactions are historically closely related to hypothetical modifications of elemental sulfur; black, translucent blue in thin layers, Magnus sulfur and Wehler blue sulfur. The presence of these modifications in ultramarine has been explained by a number of scientists for its varied colors.