Ageing-induced changes in varnish-coated oil paints: Surface and subsurface multi-technical analysis

Year: 2025

Authors: Dal Fovo A., Maestro-Guijarro L., Carmona-Quiroga PM., Fontana R., Rosi F., Cardinali MA., Romani A., Comez L., Riminesi C., Iwanicka M., Targowski P., Kowalska M., Philippidis A., Pouli P., Castillejo M., Oujja M.

Autors Affiliation: Consiglio Nazl Ric Ist Nazl Ott CNR INO, Florence, Italy; CSIC, Inst Quim Fis Blas Cabrera IQF, Madrid, Spain; CSIC, Inst Ciencias Construcc Eduardo Torroja IETcc, Madrid, Spain; Consiglio Nazl Ric Ist Sci & Tecnol Chim CNR SCITE, Perugia, Italy; Univ Perugia, Dipartimento Chim Biol & Biotecnol, Perugia, Italy; Consiglio Nazl Ric Ist Officina Mat CNR IOM, Perugia, Italy; Consiglio Nazl Ric Ist Sci Patrimonio Culturale CN, Sesto Fiorentino, Italy; Nicolaus Copernicus Univ Torun, Fac Fine Arts, Torun, Poland; Nicolaus Copernicus Univ, Fac Phys Astron & Informat, Inst Phys, Torun, Poland; Fdn Res & Technol Hellas FORTH, Inst Elect Struct & Laser IESL, Iraklion, Crete, Greece.

Abstract: Preventing varnish degradation is a major challenge in painting conservation. Despite extensive research, the mechanisms behind varnish alteration are not yet fully understood due to the complexity of the concurrent processes involved. Moreover, the extent to which organic and inorganic pigments, dispersed in various binding media within the paint substrate, influence this process remains unclear. Due to this complexity, detecting early signs of varnish degradation is a crucial step in protecting the underlying painting from irreversible damage. This study aimed to evaluate the effects of thermo-hygrometric and photochemical ageing at both surface and subsurface levels on natural (dammar resin) and synthetic (acrylic resin) coatings. These were analysed both as standalone layers and in combination with oil paint materials containing two common inorganic pigments: titanium dioxide and yellow ochre. A comprehensive suite of complementary, non-invasive techniques, spanning nano- to macroscale resolution, was employed. This optimized monitoring protocol, with potential in situ applicability, enabled high-resolution mapping of varnish degradation patterns, elucidating the complex interplay between compositional factors, environmental ageing conditions, and substrate-paint interactions. This study establishes a robust framework for evaluating material stability through the identification of early degradation markers, which can directly inform conservation strategies for painted artworks. Furthermore, it provides scientific support for varnish selection criteria, condition assessment protocols, and predictive conservation models.

Journal/Review: JOURNAL OF CULTURAL HERITAGE

Volume: 76      Pages from: 263  to: 276

More Information: The research was funded by H2020 European project IPERION HS (Integrated Platform for the European Research Infrastructure ON Heritage Science, GA 871034) , PNRR H2IOSC (Humanities and Cultural Heritage Italian Open Science Cloud) Project (IR0000029) -CUP_B63C22000730005, funded by Next Generation EU . Funding from MCIN/AEI/10.13039/50110 0 011033/FEDER, UE through the project PID2022-137017OB-I00 and from the Regional Government of Madrid through the project TEC Heritage-CM (TEC-2024/TEC-39) , and support from the CSIC Interdisciplinary Platform Open Heritage: Research and Society (PTI-PAIS) are acknowledged. Discussions with Dr. Katrien Keune are thankfully acknowl-edged. The contents reflect only the authors’ views, and the European Commission is not responsible for any use that may be made of the information it contains.
KeyWords: Non-invasive multi-analytical approach; Natural varnish; Acrylic varnish; Artificial ageing; Natural ageing; Painting conservation
DOI: 10.1016/j.culher.2025.10.003