Micro-analytical study of two 17th century gilded miniature portraits on copper

• Two gilded miniature portraits on copper support of the 17th century were studied using cutting-edge microanalytical methods.
• A multi-analytical approach was used to characterize chemically the materials of both historical items.
• From the chemical point of view, the pigments palette was fully characterized.
• Overall, the miniatures were gilded with gold leaf and shell gold.
• The identification of the two intermediate layers constitute one of the few experimental evidences on this kind of gilding.

Two gilded miniature portraits on copper support from the Evora Museum collection (Portugal) were examined and analysed by stereomicroscopy, μ-Raman spectroscopy, SEM–EDS, portable-XRF (pXRF), μ-FTIR spectroscopy and liquid chromatography coupled to diode array and mass spectrometry detection (LC-DAD-MS). Both portraits, one of a gentleman and the other of a lady, are notable paintings of comparable richness, which present several areas painted or covered with gold (namely, gold dust to compose and highlight different ornaments and gold leaf to cover the back of one of the portraits). The gold dust, the gold leaf and the materials used in the gilding technique were investigated non-invasively and non-destructively using stereomicroscopy, SEM–EDS, pXRF and μ-FTIR. The other materials of the paintings, like the inorganic pigments and extenders, were successfully identified by μ-Raman spectroscopy, while the organic red pigment cochineal lake was positively identified by LC-DAD-MS. Overall, the materials identified in these 17th century paintings are broadly consistent with those mentioned in the painting treatises of that time, or with those reported in a very limited number of material studies focused on artworks of the same kind and period.