Fabric swatches dug up from archaeological sites often look like dull brown rags, but archaeologists are putting crime lab techniques to work to uncover the colors, patterns and other revealing features of antiquated textiles.

The patterns, in particular, have helped researchers identify the dyes, paints, skills and trade routes of the Hopewell, a broad network of Native American groups who lived in the eastern part of North America about 2,000 years ago. The Hopewell in Ohio made enclosures out of earthen walls called mounds, and traded materials with people as far away as Wyoming.

Color patterns are usually invisible to the naked eye under standard lighting conditions but behave differently in the infrared (IR) and ultraviolet (UV) spectra than in visible light. So Ohio State University archaeologists employed IR and UV technology normally used to detect fingerprints to look for patterns on fabric specimens found in Ohio's Seip burial grounds. The fabrics excavated from the burial grounds are thought to be part of a canopy that was arched over the deceased 1,600 years ago.

"The camera sees what we cannot see with our eyes alone," said Christel Baldia, lead author of a report on the technique and findings published in the April issue of the Journal of Archaeological Science.