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Keywords = varnished brass

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17 pages, 8482 KB  
Article
Characterization and Identification of Varnishes on Copper Alloys by Means of UV Imaging and FTIR
by Miriam Truffa Giachet, Julie Schröter and Laura Brambilla
Coatings 2021, 11(3), 298; https://doi.org/10.3390/coatings11030298 - 5 Mar 2021
Cited by 13 | Viewed by 4696
Abstract
The application of varnishes on the surface of metal objects has been a very common practice since antiquity, both for protective and aesthetic purposes. One specific case concerns the use of tinted varnishes on copper alloys in order to mimic gilding. This practice, [...] Read more.
The application of varnishes on the surface of metal objects has been a very common practice since antiquity, both for protective and aesthetic purposes. One specific case concerns the use of tinted varnishes on copper alloys in order to mimic gilding. This practice, especially flourishing in the 19th century for scientific instruments, decorative objects, and liturgical items, results in large museum collections of varnished copper alloys that need to be preserved. One of the main challenges for conservators and restorers deals with the identification of the varnishes through non-invasive and affordable analytical techniques. We hereby present the experimental methodology developed in the framework of the LacCA and VERILOR projects at the Haute École ARC of Neuchâtel for the identification of gold varnishes on brass. After extensive documentary research and analytical campaigns on varnished museum objects, various historic shellac-based varnishes were created and applied by different methods on a range of brass substrates with different finishes. The samples were then characterized by UV imaging and infrared spectroscopy before and after artificial ageing. The comparative study of these two techniques was performed for different thicknesses of the same varnish and for different shellac grades in order to implement an identification methodology based on simple non-invasive examination and analytical tools, which are accessible to conservators. Full article
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14 pages, 2694 KB  
Article
A Preliminary Spectroscopic Approach to Evaluate the Effectiveness of Water- and Silicone-Based Cleaning Methods on Historical Varnished Brass
by Michela Albano, Silvia Grassi, Giacomo Fiocco, Claudia Invernizzi, Tommaso Rovetta, Maurizio Licchelli, Raffaella Marotti, Curzio Merlo, Daniela Comelli and Marco Malagodi
Appl. Sci. 2020, 10(11), 3982; https://doi.org/10.3390/app10113982 - 8 Jun 2020
Cited by 11 | Viewed by 4144
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 [...] Read more.
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. Full article
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