The Lady and the Unicorn tapestry (14th c.) was acquired by the Musée de Cluny in 1882. The set comprises 6 tapestries representing an allegory of the five senses. These tapestries have deteriorated, especially the colours that require several dyes, such as green or violet. These degradations result in a significant loss of information to understand the history of the tapestry's creation. Bibliography reports on the state of deterioration of the tapestry carried out by the Bregère studio in 1942, indicating the mauve colour disappearance that had become light blue on the subject's dress of the tapestry "La Vue".In the Middle Ages, it was common for the violet colour to be made with a blue dye bath (woad) followed by a red bath which could be madder, kermes or orcein. The latter is obtained from lichen, either of the Rocella types from the Mediterranean basin (sea orcein) or the land orcein found inland. This dye has been used since antiquity and was rediscovered in the Middle Ages in France in the 14th century. It is known to be very unstable and seems to have been used to make the violet of the dress' Lady turned blue today.Our study focuses on this orcein. Thus, it was necessary to experiment by extracting its dyestuff to optimise wool dyeing before analysing the samples using non-contact methods (colourimetry, hyperspectral imaging and fluorimetry). This methodology allowed recording orcein's reference spectra depending on the recipe used to constitute a database. In addition, a light degradation study was carried out on the samples before comparing the results with the signal obtained on the tapestry. This comparison would help us confirm the hypothesis on the identification of this dye and have some information on this dyeing technique.Read less <