The Art of Dating Silk Textiles

September 13, 2011

A new mass spectrometry method will allow museum scientists to date ancient silks from samples that are far smaller than what is consumed during carbon-14 dating, the only other method that can date silk.

Mehdi Moini, a research scientist at the Smithsonian Institution’s Museum Conservation Institute (Suitland, Maryland), in collaboration with colleagues Kathryn Klauenberg and Mary Ballard, has developed a new mass spectrometry method that will allow museum scientists to date ancient silks from samples that are far smaller than what is consumed during carbon-14 dating, the only other method that can date silk.

To develop the technique, the Smithsonian team looked closely at aspartic acid residues in the silk protein extruded by silk worms. Over decades, these aspartic acid residues can turn into their mirror images, switching from the L-form to the D-form in a process called racemization. Moini’s team used mass spectrometry to calculate the ratio of D- to L-forms, and to thereby determine the age of silk textiles. They performed the analysis on 100 μg samples and smaller.

The researchers evaluated their technique on samples that included fresh silk from 2010; American civil war flags; a man’s silk suit from the 1700s; Turkish tapestries from the late 1500s; Egyptian silk yarns from 993 A.D.; and silk artifacts from China’s Warring States period, which occurred between 475 and 221 B.C.