Ancient Persian silks from 934 B.C.E to 1062 B.C.E. can fetch a pretty penny from art collectors and museums, but a chemical test, described in Analytical Chemistry, has revealed that some of the fabrics on the market may not be as ancient as they claim. Silk is an organic material containing proteins made from chains of amino acids. Nearly every amino acid used in biology shares a common underlying structure (or chirality, to be precise), but over time some of the molecules can spontaneously change shape, switching into mirror images of themselves—left-handed to right. Artificial aging techniques throw this balance out of whack, however, causing far more amino acids to switch shape than one would expect, and thus leaving a telltale signature to separate forgeries from genuine, C&EN reports.