A group of French researchers have determined that processes for dying gray human hair black that were developed two millennia ago rely on nanoscale phenomena.

Philippe Walter and colleagues at the French Museums Restoration Research Center in Paris found that a recipe from the Greco-Roman era worked because of nanocrystals of lead sulfide that form inside hair shafts.

The research, which appeared in the journal Nano Letters, is another example of how nanoscale phenomena have been harnessed for eons, long before scientists (or, as the case may be, cosmeticians) understood how the processes they were using worked.

But it is hardly the only ancient use of nanotech. Indian kaajal, an ancient type of eyeliner, is riddled with nanotubes, according to research by a professor at the Indian Institute of Technology that was reported on in Small Times’ small world section in the May/June 2006 issue.