The anthraquinone components of the roots of various species of madder (like Rubia tinctorum L. and Rubia peregrina L.) have been used for millennia as red colorants in textiles, carpets, tapestries, and other objects. To understand the selection and preparation of dyestuffs in various cultures and historical periods, these dyes (mainly alizarin and purpurin) are traditionally analyzed by means of separation methods that require sampling. This contribution focuses on establishing a fast, noninvasive, and in situ analytical procedure based on visible reflectance spectroscopy for the characterization and quantification of anthraquinones in ancient wool yarns. The method was successfully applied to Coptic textiles, and the analytical results are in agreement with prior observations obtained on samples by separation techniques.