ORIGINAL PAPER Colored grounds of gilt stucco surfaces as analyzed by a combined microscopic, spectroscopic and elemental analytical approach A. Sansonetti & J. Striova & D. Biondelli & E. M. Castellucci Received: 30 November 2009 / Revised: 8 January 2010 / Accepted: 17 January 2010 / Published online: 20 February 2010 # Springer-Verlag 2010 Abstract A survey of gilts applied to stucco surfaces that specifically focuses on the compositions of their colored grounds is reported. Gilt samples of a common geographical (Lombardy in Italy) and temporal provenance (17th–18th century) were studied in the form of polished cross-sections by optical and electron microscopy (SEM-EDS), micro- Raman (μRaman) spectroscopy and Fourier-transform infrared microspectroscopy (μFTIR). Comparing samples with superimposed grounds and gilts enabled light to be shed on the choice of specific materials, their stratigraphic functions, decorative effects, and technological performances. Iron oxide pigments were found in the older grounds, sometimes in the presence of lead white (2PbCO 3 ·Pb(OH) 2 ) or minium (Pb 3 O 4 ). In more recent grounds, chrome yellow (PbCrO 4 ), chrome orange (PbCrO 4 ·PbO), cinnabar (α-HgS) and barium white (BaSO 4 ), invariably mixed with lead white, were encountered. Evidence for the use of organic mordants (colophony and wax, or siccative oil) was obtained by μFTIR. This combined μFTIR and μRaman spectro- scopic and elemental (SEM-EDS) analytical approach enhances knowledge of the composition of gold grounds, their variability and their chronological evolution. Keywords Gilding technique . Stucco . Raman spectroscopy . Colored grounds . Chrome yellow and orange . Mordant gilding Introduction Gilding is the technique of applying a metal leaf, usually gold, onto a substrate. Historically, artists frequently made use of gilding to decorate and provide a precious brightness and optical dynamism to various works of art [1]. Gildings vary in terms of the type and form of metal used, as well as in the technique of application. Several elements were considered in the manufacture of the metallic leaves (e.g., gold, silver, tin, copper or zinc), and these leaves were applied to various substrates, such as easel or mural paintings, ceramics, paper, glass or stone. Several ancient and modern treatises [2–5] report on the use of gilding techniques, and other recent papers report on analytical studies of gilts in easel paintings [6], wall paintings [1, 6–9] or on ceramic supports [9, 10]. On the other hand, only a few references mention ancient stucco gilding techniques [11–13]. Stucco decorations are among the oldest types of artwork, and they were especially important during the Baroque and Rococo periods, when the stucco material was used to mold frames, bas- and high reliefs and other architectural elements, which were often painted or gilded. Information on the precise gilding technique used is very important, not only to reconstruct the craftsman’ s technique, but also to document the monument’ s conservation history and to choose the best conservation approach, especially in the case of retouching or integration. The two chief ways of laying gold onto a surface are to use water-soluble or oleoresinous “mordants” (adhesives for fixing gold leaf). Water gilding was usually performed A. Sansonetti : J. Striova (*) : D. Biondelli Istituto per la Conservazione e Valorizzazione dei Beni Culturali CNR, via Cozzi 53, 20125 Milan, Italy e-mail: striova@icvbc.cnr.it E. M. Castellucci LENS and Chemistry Department, University of Florence, via Lastruccia 3, 50019 Sesto Fiorentino, Italy Anal Bioanal Chem (2010) 397:2667–2676 DOI 10.1007/s00216-010-3491-4