The Blue Wall Reliefs by Yves Klein in the Gelsenkirchen Music Theater (1957–1959). Examination of Materials and Creative Process

Yves Klein’s monumental blue reliefs, located in the Music Theater in Gelsenkirchen (Germany), represent a significant stage of development within the artist’s blue period, as he consolidated his monochromatic concept, expanded his use of materials, and overcame technical challenges. Our study examined the materials used by Klein, their sources and modification, and related changes in the production techniques. The focus of this paper is on the preparation of the natural sponges, the identification of binding media, and the paint application techniques used by Klein in his blue reliefs. The aim was to expand current knowledge on Yves Klein’s ultramarine blue paint, later known as IKB (International Klein Blue) and the so-called Gelsenkirchen blue. The results also provide new insights into the challenges faced by the artist when, for the first time, he integrated his work into a public space.