Analyzing the center of each strand of hair, the researchers observed the formation of tiny lead sulfide crystals, which lined up at just .00000003937 of an inch across. Since these crystals act somewhat like melanin, the natural substance that gives hair color, more crystals meant darker hair.
Walter explained that chemical engineering of such tiny structures to form quantum dots is "a current challenge in nanotechnology," and that the reaction of this ancient lead dye with hair exemplifies the sort of process that researchers are trying to develop.
In a separate study, scientists Bo Yang and Vinod Tewary at the National Institute of Standards and Technology came to similar conclusions about how self-assembling quantum dots line up, only their focus was on assemblages in semiconductor materials rather than hair.
Previously, Walter and his team studied 4,000-year-old Egyptian eye makeup housed at the Louvre Museum. They again found that lead was an important ingredient. In this case, lead chlorides and other compounds thought to confer medicinal properties, such as clearing up infections, were added to a lead sulfide base.
The Egyptians, it seems, believed a heavy application of eye makeup served double duty as both a beauty enhancer and medicine.
The 2,000-year-old Greek and Roman hair dye, however, probably was for looks only. In addition to black dye, many individuals dyed their hair red with henna and sprinkled it with gold powder and often a fresh flower or two. Hairdressing and barbershops were located in most populated regions of the ancient world.
