This paper describes the conservation of two fibrous plaster panels in the National Museums of Scotland (NMS). The panels were part of two wall friezes, designed by Charles Rennie Mackintosh for the Front Saloon of the Willow Tea-rooms, opened in Glasgow in November 1903. The panels were removed from the tearooms in the late 1970s. Some have since been exhibited in museums and galleries, although there has been controversy about the authenticity of several restored panels and their appearance as an all-white design. Paint analysis was carried out to establish the original appearance, to interpret the history of the panels and to guide the removal of the overpaints. This also helped establish the authenticity of a third panel in the NMS collection. A mounting system was devised to enable the display of the two panels as a frieze in the Museum of Scotland. -- SCMRE