The fabrics, drab and colorless in natural lighting, showed changes in colors and patterns under ultraviolet and infrared lighting. The scientists then took very small samples from those regions of the textiles that showed differences and performed conventional tests to determine whether the coloring came from dye or paints.
Conventional sampling requires that a tiny portion of the fabric be immersed in a solution that completely destroys the sample. Using forensic photography can help pinpoint exactly which portion to sample.
"It's good that they are working in this direction, but ultraviolet light is not as nondestructive as it sounds," said Irene Good, an associate of the Peabody Museum at Harvard University and an expert in ancient textiles.
Ultraviolet light induces a chemical reaction in organic materials (think sunburns or fading fabrics in a sunlight window) and could ultimately destroy an entire sample, said Good. Using infrared, which museums already employ to check for forgeries, is preferable, but in the end it's a question of what is more valuable: information or preservation?
"That is what analysts and textile conservators face every day," said Good.
