An authentication case study: Antonio Palomino versus Vicente Guillo paintings in the vaulted ceiling of the Sant Joan del Mercat church (Valencia, Spain)

Abstract

In 1695, the Valencian artist Vicente Guillo was engaged in painting the vault of the Sant Joan del Mercat church in Valencia, Spain. After preliminary work was carried out, his contract was cancelled. In 1697, Antonio Palomino, renowned for the publication of his technical treatise entitled El Museo Pictorio y Escala Optica, was finally selected as the painter in charge of decorating the vaulted ceiling of Sant Joan del Mercat. This paper reports an analytical study focused on the characterisation and discrimination of the palette and painting procedures used by Palomino and Guillo in the frescoes of Sant Joan del Mercat. For this purpose, Raman spectroscopy combined with light microscopy, scanning electron microscopy–X‐ray microanalysis, voltammetry of microparticles, X‐ray diffraction, Fourier transform infrared spectroscopy and gas chromatography–mass spectrometry has been employed. The use of gypsum as stucco material for the ground layers contrasts with the recommendations made by Palomino in his treatise about the convenience of using slaked lime‐sand mortars according to traditional fresco recipes. Although lead‐based pigments were not traditionally recommended for frescoes because of their empirically known alterations when subjected to strong alkaline fresco medium, both Guillo and Palomino used them. Palomino, probably supported by his personal experience as a painter, recommended and used Naples yellow, which has been found in a good state of preservation. In contrast, white lead areas found on Guillo's paintings have transformed into lead oxides. Other pigments found in the vaulted ceiling such as smalt, goethite, haematite, azurite and malachite have also undergone substantial changes because of the extreme temperature conditions to which they were subjected in the church. Copyright © 2012 John Wiley & Sons, Ltd.

On the stability of mediaeval inorganic pigments: a literature review of the effect of climate, material selection, biological activity, analysis and conservation treatments

“…Synergy with photodegradation and oxidation [64,66] Involved in discolouration and sulphation [106,197,199,202,203,[207][208][209] Unstable [103,123,200], but still used in wall paintings [73,193,[201][202][203] Red Red lead…”

“…Again, leaching of alkali is observed, and in some strongly degraded smalt particles showing cracks, cobalt and other divalent ions are leached as well, probably due to aggressive environmental conditions (humidity, basic pH) [88,91,96]. On top of ions lixiviation and weathering of the glass, examples of heat degraded smalt are reported in wall paintings affected by fire [103].…”

“…Azurite degrades to green compounds: malachite (CuCO 3 ·Cu(OH) 2 ) and paratacamite/atacamite (Cu 2 Cl(OH) 3 ) are some examples [28,64,111,112,[115][116][117][118]. Humidity and chloride ions from various sources cause the formation of black copper oxides (CuO) and green chlorides (nantokite CuCl, paratacamite/atacamite or botallackite Cu 2 Cl(OH) 3 [103,116,[118][119][120][121]). Azurite degrades to black tenorite CuO when exposed to heat in presence of alkali [20,68,91,103,113,114,[121][122][123], while cold alkaline conditions might not affect it [111], or cause conversion to malachite [119], or the formation of tenorite via formation of copper hydroxide Cu(OH) 2 [35,64,114].…”

Another beauty of analytical chemistry: chemical analysis of inorganic pigments of art and archaeological objects

“…Raman spectroscopy Figure 49 shows the Raman spectrum of a sample of carbon black pigment from the frescoes of the Sant Joan del Mercat church (eighteenth century, Valencia, Spain) [92]. This pigment, used since Prehistoric times, has a problematic identification and often its presence is deduced from the failure to identify other type of black pigments.…”

Raman spectroscopic analysis of a belltower commemorative wall decoration

“…Rock art and wall paintings in public places, such as caves and churches, is prevalent to deterioration caused as a result of human visitation and handling-this is found to be even more acute where the art works have been partially destroyed by heavy-handed restoration particularly in the 19th and early twentieth centuries and by deliberate acts of war and aggression: a recent example of this [39,40] is provided by the restoration of a late Renaissance wall painting in a church in Valencia which has been severely damaged by automatic gunfire and conflagration during its occupation in the Spanish Civil War in the mid-to late1930s. Raman spectroscopy has played a vital role in this particular case in the identification of the mineral pigments used originally, the location of areas of unsympathetic and incorrect restoration undertaken in the 1960s and in the early warning notice of regions of ongoing biological colonisation and degradation of the pigments near six unglazed lunettes in the church nave.…”