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- Chromatic reintegration in contemporary monochromatic unvarnished paintings: a case study based on artwork from Jorge MartinsPublication . Aleixo, Marta; Bailão, Ana; Gomes, Andreia E.; Linhares, João; San Andrés, Margarita; Nascimento, SérgioThe choice of chromatic reintegration materials for contemporary monochromatic oil and acrylic emulsion unvarnished paints is usually a problem before treatment. This kind of paintings maybe subject to abrasions, especially on the edges, fingerprints and smudges, mainly caused during handling. Being unvarnished works, chromatic reintegration becomes a more complex process as no protective layer exist over the paint. The aim of this work was to assess the materials that over performed in the reintegration of paintings from the Portuguese painter Jorge Martins. Representative mock-ups made with the artist and using his materials and techniques were artificially aged. Different types of materials, aqueous and non-aqueous, were then tested to assess the best ones. It was found that the best results were obtained with Ferrario® pigment dispersed in the Tri-Funori® binding medium and with Winsor & Newton® Designers Gouache, both aqueous and non-toxic.
- Chromatic changes in paintings of Adriano de Sousa Lopes after the removal of aged varnishPublication . Linhares, João; Cardeira, Liliana; Bailão, Ana; Pastilha, Ruben; Nascimento, SérgioThe ability to digitally remove the varnish layer during the pre-conservation diagnostic of a painting, without any chemical or physical intervention, could be an advantage because it enables the prediction of the outcome of the cleaning procedure of the protective layer and contributes to the treatment proposal. Two paintings from Adriano de Sousa Lopes were investigated by hyperspectral imaging in the visible range, before and after the varnish layer removal. The spectral reflectance was estimated in each case and its comparison used to assess the effect of the varnish layer removal. The simulated paintings with the old varnish layer were compared with those restored, with no varnish, by comparing the chromaticity coordinates and other chromatic descriptors. It was found that considering the effect of the varnish layer of each painting individually produces lower errors than considering the average of the varnish layer across paintings. It was also found that simulating the varnish layer removal without knowing the varnish transmittance produces limited results and that the errors are smaller if the chromatic content is assessed without considering lightness.
- How good are RGB cameras retrieving colors of natural scenes and paintings? — a study based on hyperspectral imagingPublication . Linhares, João M. M.; Monteiro, José A. R.; Bailão, Ana; Cardeira, Liliana; Kondo, Taisei; Nakauchi, Shigeki; Picollo, Marcello; Cucci, Costanza; Casini, Andrea; Stefani, Lorenzo; Nascimento, Sérgio Miguel CardosoRGB digital cameras (RGB) compress the spectral information into a trichromatic system capable of approximately representing the actual colors of objects. Although RGB digital cameras follow the same compression philosophy as the human eye (OBS), the spectral sensitivity is different. To what extent they provide the same chromatic experiences is still an open question, especially with complex images. We addressed this question by comparing the actual colors derived from spectral imaging with those obtained with RGB cameras. The data from hyperspectral imaging of 50 natural scenes and 89 paintings was used to estimate the chromatic differences between OBS and RGB. The corresponding color errors were estimated and analyzed in the color spaces CIELAB (using the color difference formulas ∆E* ab and CIEDE2000), Jzazbz, and iCAM06. In CIELAB the most frequent error (using ∆E* ab) found was 5 for both paintings and natural scenes, a similarity that held for the other spaces tested. In addition, the distribution of errors across the color space shows that the errors are small in the achromatic region and increase with saturation. Overall, the results indicate that the chromatic errors estimated are close to the acceptance error and therefore RGB digital cameras are able to produce quite realistic colors of complex scenarios.