Two thousand years ago, the Greeks unwittingly fabricated nanoscale crystals that appear to be identical to the quantum dots now at the cutting edge of materials science.
Unlike today’s scientists, who are investigating the dots for such uses as solar energy and lasers (SN: 6/3/06, p. 344: Quantum-Dot Leap), the ancients were exploiting them to blacken hair and probably wool. So reports a team of researchers from France and the United States in the October Nano Letters.
A hair-dye formula in an ancient text originally tipped off scientists to the Greeks’ creation, says Philippe Walter, a chemist at the Paris-based Center for Research and Restoration of the Museums of France.
Testing the formula, the team dyed blonde hair black with a mixture of water, lead oxide—an orange powder—and the alkaline chemical lime. The researchers observed that lead atoms penetrated hair shafts and bonded to sulfur atoms freed from proteins by the alkalinity. The resulting compound formed light-absorbing crystals about 5 nanometers across, Walter says.
While the dye’s nanoscale action wasn’t recognized before, its effectiveness certainly was. Hair darkeners containing lead are still in use today, Walter notes.