A Preliminary Spectroscopic Approach to Evaluate the Effectiveness of Water- and Silicone-Based Cleaning Methods on Historical Varnished Brass

Michela Albano,Silvia Grassi,Daniela Comelli,Claudia Invernizzi,Raffaella Marotti,Giacomo Fiocco,Tommaso Rovetta,Curzio Merlo,Maurizio Licchelli,Marco Malagodi

doi:10.3390/app10113982

Abstract

Soiling deposition and wrong conservation practices are among the causes of the decay process that can affect the morphological, mechanical, and compositional features of the varnish, the most exposed layer of an artefact. In this perspective, the identification of the best cleaning practices is a priority. During the 18th century, scientific instruments of the highest quality were built, and peculiar varnishes were produced to confer protection and elegance to their metal elements. For this study, based on a historical recipe, we have reproduced a peculiar spirit varnish, enriched with natural resins and colorants, and we have applied on it a synthetic soiling mixture to simulate the aging conditions. We have then performed a non-invasive multi-analytical study to monitor the effectiveness of two water-based and a silicone-based, cleaning methods, namely, water in agarose, Tween 20 (3%) in agarose, and Velvesil™ Plus. The study includes colorimetry, Fourier transform infrared (FTIR) spectroscopy and X-ray fluorescence (XRF) mapping, coupled with chemometrics. Principal component analysis applied to FTIR spectral data has been demonstrated to be a powerful tool to enhance weak variations in the IR spectra, empowering the interpretation of cleaning effect versus the application time of each cleaning test.

Highlights

Brass has always been employed for the metal components of scientific instruments due to its malleability and ductility, and to its golden aspect aimed to confer their elegance
We investigated the removal of soiling from varnished surfaces using aqueous methods in gel and a silicone-based material
We demonstrated that the effectiveness of the cleaning procedures can be evaluated through the analysis of specific IR absorbance bands, related to the inorganic fraction of the soiling mixture, and through the Ca spatial distribution, detected by X-ray fluorescence (XRF)

Summary

Introduction

Brass has always been employed for the metal components of scientific instruments due to its malleability and ductility, and to its golden aspect aimed to confer their elegance. Such a surface, in many artefacts, was protected and enriched by varnishes. In many artefacts, was protected and enriched by varnishes The role of these varnish layers is crucial, representing part of the technological value of these objects. Sci. 2020, 10, 3982 metal from the triggering of the corrosion in the alloy caused by environmental moisture, pollutants, and other decaying factors [1]. During the 18th century, the manufacturing of scientific instruments reached its apogee bearing to the use of peculiar materials and procedures that today make these objects a unique portion of the cultural heritage

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Results

Conclusion