The Chemical History of Color

Color is important. It gives life to everything people do, think, and even say. In the days when color television sets were expensive, and the corner bar was in sole possession of one, the neighborhood center became the corner bar. Color sensation is a universal human experience. From the beginning of recorded history, references to color abound in connection with every aspect of human life.

Anyone who has shared the company of three-year old children for an afternoon will recognize the conversation. Everything you say is challenged immediately with their favorite word—why? Newly arrived in the world and fascinated by all they see, three-year olds want to know the why of everything. They live in a world of mystery, wonder, and possibility—where magic is real and reality is magic. As we explore the discovery of the physics of color origin and perception, put yourself in the place of the three-year old who always wants to know why. Or put yourself in the place of the discoverers themselves who must have been filled with awe at what they learned and communicated to the world for the first time.

Thousands of tourists from all over the world flock to two island sites at opposite ends of the earth from one another for no other reason than to gaze in awe and wonder at the color phenomenon each one is famous for. Hawaii’s Green Sand Beach on the southernmost point of the Big Island boasts an entire beach covered with tiny olivine crystals that sparkle like emeralds in the tropical sun. Olivine is a common constituent of lava flows, but only in this one place has it been found of gem quality—the crystals in this case seem to have floated on a former lava lake. Around the globe in the North Atlantic, a unique body of water known as the Blue Lagoon on Iceland’s Reykjanes peninsula plays host to about 400,000 visitors a year who come to take a dip in this unique body of water—also an indirect product of an ancient lava flow flooded by the transforming effluent from a nearby geothermal power plant. What is it about some materials that give rise to these and so many other wonderful colors? Why are other substances colorless, and can we modify them to produce color? The answers to these questions are not simple, and they involve awareness of several important insights regarding the nature of matter, particularly atoms and molecules.

As one might expect, following Perkin’s discovery, many industrial dyers and chemists began systematic searches for additional aniline colors by mixing aniline with just about anything they could think of Among these experimenters was François Emmanuel Verguin (1814–1864) who, as early as 1858, discovered a red dye, later called aniline red, made by treating aniline with anhydrous stannous chloride.

One of the many things that the German dye companies excelled at was seeing the long-range and global picture and acting upon it. They went very large-scale on virtually every front, utilizing all the weapons that science and technology had to offer. They found that doing so enabled them to synthesize two important natural colorants, indigo and alizarin, thus eliminating the industry’s dependence on natural products and imports—the dye industry could now not only be self-sufficient, but could use the know-how generated in these key syntheses to make many other derivatives. In addition to setting up large laboratories that employed hundreds of chemists, they built libraries that had subscriptions to virtually every scholarly science journal in the Western world, they established dedicated bureaus to patent discoveries, and they virtually “wrote the book” on abstracting services by having these offices work around the clock and not only in the area of chemistry, but in every other domain that might afford them related knowledge—biology, the emerging area of biochemistry, pharmaceuticals, photography, and explosives.

This final chapter will alliteratively pick up many topics that fell outside the trajectory traced by the history–chemistry—color interface in the previous seven chapters. We will see how colored additives affected the food quality of the past and, by extension, how color has affected, and continues to influence, so many other aspects of our daily lives.