High brightness and small spot working conditions revealed the development and distribution of calcium oxalates in the binding media, which seem to be responsible for the darkening. To elucidate the causes involved in the darkening of the sample from the vaults a set of synchrotron μXRD and μFTIR experiments have been carried out on these samples at the ESRF (ID18F and ID21, respectively). It is interesting to notice that the first remained unaltered, while the gilded vault mouldings look almost black, due to the darkening of the organic material. These preliminary results demonstrated that gilded decorations were made by the application of a gold foil on a mordant substrate on a gypsum base, while the mouldings of the vaults seem to be gilded on a bol with a glaze on top of the gold leaf. Cross sections from two different gilded decorations were studied by means of optical microscopy and electron microscopy and EDS to determine the statigraphy and elemental composition, and by means of FTIR coupled to a microscope to determine the binding media associated to each layer. In this paper seventeenth century gilded paintings from the crypt of Sant Benet de Bages, a medieval monastery in the Catalonia region of Spain, near Barcelona, have been studied. The external gilding was applied at the beginning of the 19th century using mordant oil (linseed oil). This is the first time that lead chromate has been detected in gildings. However, complete characterisation of the medallions required the use of other techniques such as mass spectrometry and scanning electron microscopy- energy dispersive X-ray.
Conclusion: The non-invasive techniques provided useful information about the characterisation of the components of the golden medallions. Another golden layer applied in oldest time period was also found. This yellow pigment (lead chromate) and the layers of bole and white lead were characterised in cross-sections prepared from samples taken from the medallions in which the golden layer was missing. A layer of lead chromate with some lead sulphate was between the alloy and the support. However, copper, silver and zinc were also found. Results: The leaf adhered to the surface was primarily a gold alloy.
Cross-sections of golden support were also performed and studied by SEM-EDX. The gilding of the medallions from the Mudejar palace of Sevilla Alcazar was investigated, and their components were characterised using non-invasive (in situ and laboratory) techniques such as X-ray fluorescence, μ-Raman, infrared spectroscopy, X-ray diffraction and scanning electron microscopy coupled with energy dispersive X-rays. The identification of the materials and processes to make the gilding and the use of noninvasive techniques for gilding study is still an open problem. There are various ways to make gold leaf adhere to a large surface area. False gold was also found in the form of copper-zinc powders or silver covered with resin. Background: The first stable material used to create a gilded surface was gold.
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