Multi-Spectroscopic Approach for the Non-invasive Characterization of Paintings on Metal Surfaces

Abstract

The aim of this study is to propose a non-invasive multi-spectroscopic approach for the characterization of oil painting artworks that use a copper plates as substrate in place of a canvas. Indeed, in the last decade, many studies have been conducted on artworks made of single materials (e.g., paintings, stones, metals). However, the characterization and conservation of composite artifacts has never be fully investigated even though many masterpieces were created using this particular technique. In this work, several spectroscopic techniques such as Infrared Spectroscopy (FTIR), Energy-Dispersive X-Ray Fluorescence spectroscopy (EDXRF), and high spatial resolution Field Emission Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (EDS), and Optical Microscopy (OM) were performed. The obtained results allowed to fully characterize the micro-chemical and microstructural features of the painted surfaces and of the metal plate. Particularly effective was the use of MA-XRF, resulting in the chemical map of the painted surfaces. Furthermore, traces of the mechanical preparation of the plate were found under the painted layers. Finally, the interface area between the paint film and the metallic support was characterized at a micro scale. This was particularly important in order to identify the degradation products formed by the interaction between the fatty acids of the binder and copper-based substrates.

Non-Invasive Technical Investigation of English Portrait Miniatures Attributed to Nicholas Hilliard and Isaac Oliver

“…Characterised by a minute and impeccable technique and a specific purpose, and offered as a personal gift or to demonstrate devotion, portrait miniatures were painted on a vellum support glued to a playing card, with pigments generally bound in gum Arabic [1]. Other substrates included copper in the 17th century [2][3][4] as well as ivory from the beginning of the 18th century [5][6][7].…”

Non-Invasive Assessment of PVA-Borax Hydrogel Effectiveness in Removing Metal Corrosion Products on Stones by Portable NMR

“…In particular, in the case of copper and its alloys, corrosion is a chemical attack mainly promoted by the affinity of metals and pollutants (i.e., sulfur, carbon dioxide, chlorides). This process leads to a corrosive layer called patina [ 5 , 6 ], which can be protective (noble patina) or unprotective (vile patina) [ 7 , 8 , 9 ], depending on the concentration of pollutants and acid rain. As a result, geographic location, precipitation, and pollution level all have an impact on patina composition and morphology [ 9 , 10 ].…”

“…As a result, geographic location, precipitation, and pollution level all have an impact on patina composition and morphology [ 9 , 10 ]. So, the atmospheric exposure of copper produces the oxidation-reduction reactions leading to different corrosion products: copper(I) oxide which is red, copper(II) oxide which is black, black copper sulfide, various colored salts and nantokite, green-blue atacamite and clinoatacamite [ 6 ]. These corrosion products are responsible for the discoloration of the stone [ 1 , 11 ].…”

“…Generally, corrosion is activated by acidic conditions, but it can also take place in an alkaline environment [ 11 ]. The result of iron corrosion will not be a patina adhered to the metal surface but a powdery rust layer produced by electrochemical processes [ 6 ]. So, the rust consists of the stratification of the oxides, usually green hydrated magnetite, black anhydrous magnetite and, only externally, the ferric hydroxides [ 6 ], which are responsible for cervices formation in the stone surrounding the metallic part [ 11 ].…”

“…The result of iron corrosion will not be a patina adhered to the metal surface but a powdery rust layer produced by electrochemical processes [ 6 ]. So, the rust consists of the stratification of the oxides, usually green hydrated magnetite, black anhydrous magnetite and, only externally, the ferric hydroxides [ 6 ], which are responsible for cervices formation in the stone surrounding the metallic part [ 11 ]. Moreover, also when iron is covered by lead a damage to the stone should be expected because lead itself can be attacked [ 11 ].…”