Identification of green pigments and binders in late medieval painted wings from Norwegian churches

Elena Platania,Noëlle L.W Streeton,Anna Lluveras-Tenorio,Anna Vila,David Buti,Francesco Caruso,Hartmut Kutzke,Arne Karlsson,Maria Perla Colombini,Einar Uggerud

doi:10.1016/j.microc.2020.104811

Abstract

Green pigments in micro-samples taken from three late-medieval painted objects from Norwegian churches have been investigated with the aim to characterize their constituents and understand how they relate to damages observed in passages containing green paints. The cross-sections were analyzed by optical microscopy under visible and UV light, Scanning Electron Microscopy coupled with Energy Dispersive X-Ray Spectrometry and vibrational spectroscopies (Raman, ATR-FTIR). In addition, Gas Chromatography coupled with Mass Spectrometry was employed for the characterization of binding media, using a derivatization methodology recently developed for the detection of metal soaps in paint samples. This extensive characterization aided the identification of the individual constituents and the stratigraphy of green paints. It also builds the foundation for future ageing studies that can provide better insights into the mechanisms of the processes at stake in selective delamination of paints containing copper complexes.

Highlights

The cross-sections were analyzed by optical microscopy under visible and UV light, Scanning Electron Microscopy coupled with Energy Dispersive X-Ray Spectrometry and vibrational spectroscopies (Raman, Attenuated Total Reflectance (ATR)-FTIR)
Gas Chromatography coupled with Mass Spectrometry was employed for the characterization of binding media, using a derivatization methodology recently developed for the detection of metal soaps in paint samples
Cross-sections were analyzed with optical microscopy under UV and visible light, Scanning Electron Microscopy coupled with Energy Dispersive X-Ray Spectrometry (SEM-EDX), Raman Spectroscopy, ATR-FTIR and Gas Chromatography coupled with Mass Spectrometry (GC-MS)

Summary

Introduction

Northern European painters active in the 15th and 16th centuries made extensive use of neutral or basic copper acetates [1,2] These green compounds are corrosion products obtained by exposing copper plates, strips or foils to different acidic substances. Vinegar seems to have been most common, curdled milk, ammonium salts, honey and wine lees could have been used [1,3] These copper compounds are described by the umbrella term “verdigris”, but differ from each other in terms of manufacturing procedures and purification, degradation patterns, and coordination environment of Cu(II) [3,4,5,6,7]. Despite the large number of articles on the reproduction of varieties of verdigris [3,4,5,8,9,10,11], it is not always possible to identify unambiguously the type of copper-based pigment found in a paint sample

Methods

Results

Conclusion