Non-invasive analytical techniques applied to characterize the components of ancient golden medallions

Abstract

Background: The first stable material used to create a gilded surface was gold. False gold was also found in the form of copper-zinc powders or silver covered with resin. There are various ways to make gold leaf adhere to a large surface area. 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. 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. Cross-sections of golden support were also performed and studied by SEM-EDX. Results: The leaf adhered to the surface was primarily a gold alloy. However, copper, silver and zinc were also found. A layer of lead chromate with some lead sulphate was between the alloy and the support. 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. The support was composed of gypsum. Another golden layer applied in oldest time period was also found.

The Structure and Chemical Composition of Wall Paintings From Islamic and Christian Times in the Seville Alcazar

“…; Pérez‐Rodríguez et al . ). All these wps were made using animal glue and oils over gypsum plaster.…”

“…Stucco decoration is present in many parts of the Seville Alcazar, in particular in the Mudejar Palace. The stucco technique has been studied in detail for the golden medallions, revealing mixtures of mortars, based mainly on gypsum (Pérez-Rodríguez et al 2013). For the studied wps (except wps 5 and 6), portable XRF revealed the presence of Ca and S, and portable XRD that of gypsum and calcite.…”

“…; Pérez‐Rodríguez et al . ). However, wall paintings on the upper floor dating from the reign of the Catholic kings were covered long before these works, and were thus protected for a long time, until they were rediscovered at the end of the 20th century.…”

“…Recent studies of the wall paintings in the Alcazar Palace have underlined the difficulty of obtaining information about the original painting technique and materials used. Most of the wall paintings have been modified several times, mainly during restoration works carried out in the 19th century, especially on the ground floor of the Mudejar Palace (Almagro et al 2010;Pérez-Rodríguez et al 2013). However, wall paintings on the upper floor dating from the reign of the Catholic kings were covered long before these works, and were thus protected for a long time, until they were rediscovered at the end of the 20th century.…”

Ceramics from the Alcazar Palace in Seville (Spain) dated between the 11th and 15th centuries: Compositions, technological features and degradation processes

“…This technique provides precise information about the superficial crystalline structure (depths of about 1 m) and composition [45].…”