The manuscripts from the old monastic library of the abbey of Mont Saint-Michel, preserved for the major part in the heritage library of Avranches (France, Normandy), constitute a prestigious testimony of the scriptorium practices between the 10th and the 13th century. This corpus is at the center of a vast interdisciplinary project (EMMA of the Mont Saint Michel) aiming at analyzing and characterizing the different constitutive materials encountered in the manuscripts, such as parchments, inks, and coloring materials. The information obtained will give insight into the copyists and artists practices and to their evolutions, and will allow the comparison with materials used in other scriptoriums from the same period. To start, the project focused on the manuscripts produced in the Mont Saint Michel in the 11th century, and non-destructive point analyses were first conducted. This approach turned out to be insufficient and not representative in the case of highly illuminated manuscripts, where decorations present a large range of colors and materials with sometimes different pigments to represent the same color (figure). In addition, the presence of an important text hidden by a dark colored background in one of the manuscripts convinced the team to bring certain manuscripts to Paris to perform chemical imaging analyses. Hyperspectral imaging in the visible and near-infrared range and X-ray fluorescence imaging, supported by classical scientific imaging (visible photography, UV and infrared reflectance, and UV fluorescence), were then combined to characterize the coloring materials of some important decorations and to read hidden inscriptions. The combination of these chemical imaging techniques also provided information on the association of materials (mixing, superposition), corrections, and more generally on the practices of illumination, which finally appeared more complex than initially thought.