Effect of tempera paint composition on their superficial physical properties- application of interferometric profilometry and hyperspectral imaging techniques

• Published in: Progress in organic coatings 2018-04, Vol.117, p.56-68
• Main Authors: Pozo-Antonio, J.S., Barral, D., Herrera, A., Elert, K., Rivas, T., Cardell, C.
• Format: Article
• Language: English
• Subjects: Artists; Binary mixtures; Calcium sulfate; Composition effects; Conservation; Damage assessment; Hematite; Hyperspectral imaging; Imaging techniques; Interferometric profilometry; Interferometry; Morphology; Paints; Particle size; Physical properties; Pigments; Reflectance; Scanning electron microscopy; Spectrophotometry; Stereomicroscopy; Tempera paint mock-up; Thermogravimetry; Weathering; X-ray diffraction
• ISSN: 0300-9440; 1873-331X
• DOI: 10.1016/j.porgcoat.2018.01.007

•Application of interferometric profilometry and hyperspectral imaging techniques for tempera paints.•Evaluation of superficial physical characteristics (roughness, reflectance and color) of paint mock-ups.•Influence of pigmentś composition, grain size and type and concentration of binder on the superficial physical properties.•Pigments impurities and neoformed minerals play a key role on superficial physical properties of paints. Interferometric profilometry and hyperspectral imaging techniques combined with traditional analytical techniques such as spectrophotometry, stereomicroscopy, X-ray diffraction, scanning electron microscopy, particle size analysis, and thermogravimetry were used to characterize tempera paint mock-ups. These paint mock-ups were prepared as binary mixtures made by mixing either egg yolk or rabbit glue binders with one of ten pigments traditionally used by mediaeval artists, namely lime, calcium sulfate, white lead, minium, hematite, cinnabar, azurite, lapis lazuli, blue smalt and malachite. We evaluated the effects of mineralogical composition, pigment particle size and morphology, as well as the type and concentration of the binder on the physical properties of the paintś surface. Results showed that all the above compositional aspects had a direct influence on the paintś color, reflectance, and roughness. Moreover, mineral impurities and neoformed minerals due to pigment-binder interaction during paint preparation had a crucial effect on the superficial physical properties of paints. The analytical results proved the usefulness of interferometric profilometry and hyperspectral imaging techniques for the characterization of paint surfaces. The gained information will help conservation specialists in the evaluation of the impact of conservation treatments on the paint surface and the assessment of surface damage caused by weathering processes.