Fragments of the coloured layers found on the church facade of the certosa in Pavia (Italy) were analysed by x-ray diffraction polarizing microscopy and scanning electron microscopy. The fragments were identified as the remains of two different restoration treatments, calcium oxalates and amorphous silica and were identified as respectively. The first treatment was carried out prior to the 19th century and the second in 1903-1927. A third group of samples showed a brown pattina of polyester resin and ascribes to a post 1950 restoration. 11 bibliographic bibliographic references, tables, photographs, micrographs.