Volume 84 Issue 37 | p. 12 | News of The Week
Issue Date: September 11, 2006

Still Dyeing After 2,000 Years

Ancient formula, now re-created, darkens locks with lead sulfide nanoparticles
Department: Science & Technology
News Channels: Nano SCENE
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DARK CRYSTALS
Within 72 hours, PbS nanocrystals darken blonde hair (left) to black (right).
Credit: Nano Lett.
8437notw7_hair
 
DARK CRYSTALS
Within 72 hours, PbS nanocrystals darken blonde hair (left) to black (right).
Credit: Nano Lett.
[+]Enlarge
LEADEN LOCKS
Lead concentration (green) within a hair increases over time (left, after six hours; right, after 72 hours).
Credit: Nano Lett.
8437nanotechimgs
 
LEADEN LOCKS
Lead concentration (green) within a hair increases over time (left, after six hours; right, after 72 hours).
Credit: Nano Lett.

Nanotechnology may seem like the latest fad in beauty products, but a new report suggests that people have been using nanomaterials to improve upon nature for at least 2,000 years. According to researchers in France, an ancient hair-coloring concoction turns tresses black via the formation of lead sulfide nanoparticles within the hair shaft (Nano Lett., DOI: 10.1021/nl061493u).

"During the second century C.E., Claudius Galen, the most famous doctor in the Roman Empire, described exactly how to use a mixture of lead oxide and slaked lime [Ca(OH)2] to dye hair black," explains Philippe Walter, a senior scientist at the Paris-based CNRS Research & Restoration Center of Museums in France, who spearheaded the research. Applied as a paste, the lead-based formula strips sulfur from amino acids in the hair's keratin proteins and forms darkly colored PbS within the hair.

Similar formulas for dyeing hair and wool were recorded during the medieval period and the Renaissance and by 18th-century chemists in France. The coloring product Grecian Formula still uses this lead-based chemistry to gradually darken gray hair.

Working in collaboration with scientists at L'Orèal, Walter and colleagues re-created Galen's recipe and studied progressively darkening hair with modern analytical techniques. They found that the PbS forms quantum-dot-like crystals about 5 nm across. "What is particularly surprising in this reaction is that, despite the structural complexity of hair and its relative chemical inertness, metal sulfide nanoparticles easily crystallize and get organized inside this biomaterial," Walter notes.

In contrast to modern nanotechnology, Walter adds, the dyeing process uses basic chemistry techniques and inexpensive natural materials.

 
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