The first evidence of the polychromy on the stucco decoration in the Archbishop's Chateau - Sala Terrena (Kroměříž, Czech Republic)

• Multianalytical analysis of one of the first stucco decoration in Sala Terrena. • The first discovery of color accents in the facial area of stucco sculptures. • Determination of used decoration technique of Baldassarre Fontana. This interdisciplinary paper presents the results of an examination of the original coloring as well as the later modifications of stucco decorations, authored by the sculptor and stuccoer Baldassarre Fontana. The rich stucco decoration adorns the Archbishop’s Chateau in Kroměříž, which, together with its gardens, is listed as a World Heritage Site (UNESCO). The detailed material investigation employed a multianalytical approach, comprising polarising light microscopy (PLM), Fourier-transform infrared spectroscopy (FTIR/ATR), and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). Next, Raman microspectroscopy (µRS) was used as a complementary method, while X-ray powder diffraction (XRPD), including X-ray powder microdiffraction (µXRPD), was used to ascertain the phase composition of the pigments. The earliest scheme features a restrained white monochrome over lime-based finishing layers, locally accented by iron-oxide red-brown details (e.g., eyes, lips). Multiple thin scialbo (limewash) strata were identified. Petrographic features indicate lime–gypsum technology with occasional hydraulic traits. Later interventions include a 19th-century light-green repaint containing copper acetoarsenite (Paris green), followed by overpaints from the 19th to the 20th century with zinc white and TiO₂ (anatase) extenders. FTIR-ATR and μRS detected secondary calcium oxalates related to surface alteration and signals consistent with a drying-oil class binder on selected elements. These markers refine the chronology of treatments and inform conservation strategies, supporting selective uncovering and stabilization of significant layers