After the paint has dried: a review of testing techniques for studying the mechanical properties of artists’ paint

Heritage Science

Table 1 Summary of the techniques and defining characteristics (age of the paint, type of samples, the amount of strain applied to the sample, how invasive the technique is, and the relevant mechanical properties) for each technique discussed within this review.

Technique	Paint age	Sample type	Applied strain	Sample size	Invasiveness	Relevant data
Tensile testing	Dried/aged paint	Model systems	Large strain	Bulk	Invasive	Elastic stiffness, ultimate mechanical properties (\(E,\,e_{f},\,\sigma _{\mathrm {T}}\))
Dynamic mechanical analysis	Dried/aged paint	Model systems	Small strain	Bulk	Invasive	Solid/liquid-like behavior (\(E^{*},\,\mathrm {tan}\phi\))
Shear rheometry	Fresh Paint	Model systems	Small strain	Bulk	Invasive	Viscosity (\(\eta\))
Quartz crystal microbalance	Fresh & dried/aged paint	Model systems	Small strain	Thin-film	Invasive	Elastic stiffness, swelling (\(d\rho ,\,\|G^{*}\|\rho ,\,\phi\))
Nanoindentation	Dried/aged paint	Model systems & Historic samples	Small strain	Single point/small sample size	Minimally invasive	Elastic stiffness, hardness (\(E_{r},\,H\))
Laser shearography	Dried/aged paint	Model systems & Historic samples	Small strain	Area of painting	Non-invasive	Strain maps
Finite element \(\mathrm {Analysis^{+}}\)	Fresh & dried/aged paint	Model systems & historic samples	Simulated large and/or small strain	Any sample size	–	Predictive mechanical responses
Vibration Studies	Dried/aged paint	Model systems	Small strain	Area of painting	Minimally invasive	Damage risk
Single-sided nuclear magnetic resonance	Dried/aged paint	Model systems & historic samples	_	Single point/small sample size	Non-invasive	Comparative rtiffness

Definitions for mechanical properties in relevant data: E: elastic modulus, \(e_{f}\): failure strain, \(\sigma _{\mathrm {T}}\): ultimate tensile strength, \(E^{*}\): complex elastic modulus, \(\mathrm {tan}\phi\): loss tangent, \(\eta\): viscosity, \(d\rho\): areal density, \(|G^{*}|\rho\): magnitude of the complex shear modulus multiplied by the density, \(E_{r}\): reduced elastic modulus, H: hardness. \(^{+}\)Indicates that the technique is a numerical method