• Europium
• lanthanides
• DSC
• SPME
• GC-MS
• SEM
• Airyscan
• confocal fluorescence microscopy
• optical microscopy
• paint film formation
• paint curing
• protein labelling
• paint microstructure
• tempera grassa
• tempera paint
• oil paint

The 15th century has been a transitional period during which Italian artists experimented with siccative oils in addition to traditional binders, mostly based on egg, casein, and animal glue. These developments led to the adoption of new painting techniques based on the combined use, in the same paint layers, of lipid and protein binders (an emulsion of protein binder and oil) and oil paint with protein-coated pigments.
Previous studies demonstrated that the preparation method plays a crucial role in determining the chemical and physical properties of the paints, thus implying that different methods of preparation would result in distinct microstructures. The objective of this study was to characterize the microstructure and the chemistry associated to the film formation of paints based on drying oils and proteinaceous media prepared using different formulations and preparation methods.
To this aim, modern replicas of tempera grassa (an emulsion of protein binder and oil: tg) and protein coated pigment (oil paint with protein-coated pigment particles: pcp) paints were produced, as well as oil and tempera paints as control samples. These replicas were produced using known amounts of lead white and ultramarine blue, as pigments, and egg white and linseed oil, as binders.
To study the microstructure, proteins were labelled with a luminescent tag by functionalizing the egg white with 5-(4,4,4-trifluoro-3-oxobutanoyl)thiolane-2-sulfonyl chloride, acting as the luminescence sentitizer, and Europium. Oil, instead, was treated with Neuro-DiO, a readily available fluorescent dye. The labelled paints were studied with optical microscopy, confocal microscopy and scanning electron miscroscopy (SEM).
The chemistry was studied by registering the drying times, measuring the kinetics of reaction with oxygen (oxygen uptake by gravimetry), determining the molecular profile of volatile compounds emitted during the curing by solid phase micro extraction in conjunction with gas chromatography coupled with mass spectrometry (SPME-GC-MS) and evaluating the peroxide content and kinetics of radical chain reactions with differential scanning calorimetry (DSC).