Creating the illusion: The marble and stone-like decoration of the main altarpiece of St. Francis church, in Viseu

The paper presents an innovative interdisciplinary study focusing on the gilded/polychrome decoration emulating stone-like surfaces of a Rococo Retable from Saint Francis Church in Viseu, Portugal. This study was undertaken within a 3-year research project, abbreviated Gilt- Teller (http://www.gilt-teller.pt). For the characterization of the altarpiece's polychromy a representative number of samples were analyzed using a multi-technique methodology: Optical Microscopy coupled with fluorescent staining tests, microFTIR/FTIR and microRaman spectroscopy, micro-computerized tomography, Scanning Electron Microscopy coupled with energy dispersive X-ray spectrometry. Preliminary results reveal the stratigraphical and compositional characteristics of the polychromy: ground layers made of gypsum, anhydrite, calcium carbonate and animal glue; bole layers of red ochre color (Hematite); Au/Cu/Ag metal leaf, coated with shellac; marble-like polychromy made with blue, white and red pigments (Prussian blue, Lead white, Hematite, Vermillion) and "golden particles" (Cu-Zn alloy ink-type) applied in the form of fine lines on their shaft or on the round-shaped base of the columns.