The Lady and the Unicorn is the mysterious and must-see masterpiece at the Cluny Museum, in Paris. Little is known about these six impressive tapestries, apart from the fact that significant colour differences can be observed in the weaving. With cutting-edge measuring devices that scan the wall hangings on-site, then at the Archaeoscience laboratory in Bordeaux (southwestern France), researchers try to determine which dyes have been used on the wool and silk fibres. This research could answer visitors’ questions, help conservators identify the restored areas, and also be useful for the study of thousands of other textile works that form part of our heritage.