Materials and techniques of gilding on a suite of French eighteenth-century chairs

Abstract

This paper describes the technical study of a suite of French Rococo chairs at the J. Paul Getty Museum with original eighteenth-century gilding preserved under layers of restoration. A variety of analytical methods was employed to identify and characterize the materials of the preparatory layers and gold alloys including optical microscopy, digital image analysis, polarized light microscopy, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), Raman spectroscopy, and X-ray diffraction (XRD). The materials and techniques were compared with descriptions of French eighteenth-century gilding practices in contemporary artists’ treatises. Both burnished and unburnished original gilding, employing distinctive techniques, were found. The study was particularly focused on the gold alloys and the support layer for burnished gilding, a mixture known as assiette in French and as bole in English. In addition to the original gilded surface, several subsequent campaigns of gilding executed with the same eighteenth-century techniques were present on the chairs and visually indistinguishable from the original gilding. The alloy of the gold leaf used in each campaign was characterized through quantitative SEM-EDX via a calibration generated from the SEM-EDX data from gold standards. Characterization of the gold alloys proved to be a vital tool for the interpretation of the layer structure and identification of original gilding.