Polychromy on medieval ivories from the LVR-LandesMuseum, Bonn

Abstract

The Rheinische Friedrich Wilhelms- Universitat and the LVR-LandesMuseum, both in Bonn, have together initiated a research project to address several questions concerning colour applied to ivories in the Middle Ages. The objectives of this project are, first, to evaluate non-destructive methods to analyse pigments and binders on ivory, and secondly to determine if a unified approach to ivory polychromy, notably on technical grounds, existed in the Middle Ages.The LVR-LandesMuseum Bonn was founded by Karl August Freiherr von Hardenberg (1750-1822), who established the Museum Rheinisch-Westfalischer Alterthumer, or the Museum of Rhenish- Westphalia antiquities, on 4 January 1820.1 The museum's collection of ivories, one-third of which have been purchased or donated since the 1950s,2 remains little known - the exact number is still to be determined - and ranges from a late antique pyx to a baroque statuette. A small but significant number of ivories are from the Middle Ages, and all medieval ivories thus far examined show significant traces of polychromy, thus prompting the current project.The question of polychromy on medieval ivories remains one of the pressing questions in the field. The LVR-LandesMuseum project seeks to further the understanding of medieval techniques of preparing and applying polychromy, and the identification of pigments and binders. A better knowledge of these issues will help scholars identify the place of origin, give precision to questions of dating, contribute to provenance history, as well as clarify previous restoration and conservation treatments. For Gothic ivories in particular, a number of important studies have already been undertaken.3 In an extensive project of the late 1990s, Juliette Levy, Agnes Cascio and Bernard Guineau documented traces of polychromy on more than sixty Gothic ivory statuettes at the Louvre, as well as important pieces in international collections.4 Their research revealed that, in the thirteenth century, the use of a bole of oil, resin and ochre pigments was common, and that gilded orphrey borders were evidence of authenticity.5 In the early fourteenth century, a red bole made with cochineal seemed to be used beneath a wide band of gilding with vegetal motifs.6 Other colours used less frequently are blue, red, green and black for enhancing eyes, mouth, hair, attributes, and highlighting the inner parts of cloaks. Andrea Wahning conducted further studies on the collections of the Badisches Landesmuseum in Karlsruhe, and Manfred Koller examined in detail the polychrome on the ivories at Klosterneuburg. 7 According to Wahning's study, the pigments used were azurite or ultramarine blue, vermilion or red lead, green verdigris or green earth and vine black or ivory black. She suggests that the binders might have been either egg white or gum arabic.8 Although still unpublished, the most comprehensive examination to date was a project undertaken by Jana Sanyova and Vincent Cattersel at the Royal Institute for Cultural Heritage, Brussels (KIKIRPA). They presented the results from a fifteenth-century altarpiece at the Memling Museum Sint-Janshospitaal in Bruges at a conference in 2012 in Bonn.9 Among other methods, the KIKIRPA group used Fourier-Transform infrared spectroscopy (FT-IR) for analysing binders. The LVR-LandesMuseum project follows in their footsteps in adopting this technique.10A handful of historical texts describe the practice of applying colours to ivory carvings. The well-known On the diverse arts, written by the twelfth-century Theophilus Presbyter, describes the general use of cochineal red, and a glue made from sturgeon bladder for gilding.11 Other lesser-known sources are relevant to questions concerning medieval recipes for ivory polychromy, namely the ninth-century Mappae Clavicula, which contains a chapter on the 'Colouring of Bone, Horn and Woods',12 and a text by Heraclius from the tenth century that describes the technique of gilding ivory. …