A Multiscale In-Situ Experimental Method for Characterizing the Mechanical Response of Oil Paint

The mechanical behavior of historical oil paint is governed by complex, multiscale chemo-mechanical processes that evolve over decades. Yet, existing mechanical testing approaches cannot fully characterize its tensile response or resolve the microscale deformation and damage phenomena that drive cracking and delamination in historical artworks.

The aim of this work is to develop an experimental method capable of capturing the mechanical response of small-sized paint samples and linking local deformation and damage mechanisms to their overall tensile behavior.

A novel methodology is introduced that combines in-situ micro-tensile testing and high-magnification optical profilometry with full-field Digital Image Correlation for the first time in oil paint research. The method enables the construction of multiple true stress-true strain curves and the extraction of mesoscopic and macroscopic mechanical properties from a single experiment, allowing statistically meaningful characterization from minimal paint material.

The mesoscale and macroscopic responses provide key mechanical properties (Young's modulus, yield strength, ultimate tensile strength, strain at break, and Poisson's ratio) consistent with values reported in the literature. Full-field measurements reveal strain localization near pigment-rich regions, where damage accumulates and microcracks initiate. The tested aged samples consistently exhibit increased stiffness and brittleness, while differences in chemical formulation (Prussian Blue versus Titanium White pigments) lead to distinct ductile or brittle responses.

The proposed methodology enables comprehensive multiscale mechanical characterization of oil paint and captures the deformation mechanisms underlying aging and composition-dependent behavior, representing an important step toward the mechanical characterization of original historical paint material.