Effect of a SO<sub>2</sub> Rich Atmosphere on Tempera Paint Mock-Ups. Part 1: Accelerated Aging of Smalt and Lapis Lazuli-Based Paints
The behavior of historic tempera paints exposed to pollutant gases is an important issue when developing conservation strategies. In this work, binary tempera paint mock-ups that were made with either smalt or lapis lazuli pigments mixed with either rabbit glue or egg yolk binders were exposed to an...
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| Format: | Article |
| Language: | English |
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MDPI AG
2020-05-01
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| Series: | Minerals |
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| Online Access: | https://www.mdpi.com/2075-163X/10/5/427 |
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| author | José Santiago Pozo-Antonio Teresa Rivas Amelia Dionísio Diana Barral Carolina Cardell |
| author_facet | José Santiago Pozo-Antonio Teresa Rivas Amelia Dionísio Diana Barral Carolina Cardell |
| author_sort | José Santiago Pozo-Antonio |
| collection | DOAJ |
| description | The behavior of historic tempera paints exposed to pollutant gases is an important issue when developing conservation strategies. In this work, binary tempera paint mock-ups that were made with either smalt or lapis lazuli pigments mixed with either rabbit glue or egg yolk binders were exposed to an SO<sub>2</sub> accelerated aging test in order to find out more about the forms and mechanisms of alteration resulting from pigment-binder interaction. To this end, spectrophotometry, hyperspectral image analysis, and profilometry were used to study macro-scale, physical changes taking place on the surface of the paints, affecting color, gloss, reflectance, and roughness. Likewise, chemical and mineralogical changes were evaluated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (ATR-FTIR), polarized light microscopy (PLM), and scanning electron microscopy with micro-analysis (SEM-EDS), which was also used to visualize micro-texture changes in the paints. The smalt-based tempera showed a higher degree of deterioration than the lapis lazuli-based tempera, in particular a notable whitening related to the precipitation of sulfate-rich salts and to binder and pigment chemical alterations. Moreover, whereas aged egg yolk-based paints showed visible color change due to damage to the oily binder and the pigments, the most evident change in rabbit glue-based paints was binder loss. The alteration suffered by the pigments varied in line with their composition; thus, smalt (blue cobalt-containing glass) grains were more sensitive to SO<sub>2</sub> exposure than lapis lazuli-(Na,Ca)<sub>8</sub>[(S,Cl,SO<sub>4</sub>,OH)<sub>2</sub>|(Al<sub>6</sub>Si<sub>6</sub>O<sub>24</sub>)]-crystals. In the smalt grains, the SO<sub>2</sub> test caused K<sup>+</sup> leaching from the glass matrix, which was detected by means of K/Co ratios, but the lazurite crystals (main component of lapis lazuli) were unaffected (regardless of the binder used in the tempera). The most likely source of the crystallized sulfate rich salts were the impurities that were detected in association with the natural lapis lazuli pigment, i.e., calcite and diopside. Indeed, the precipitation of efflorescences is the main cause of the optical changes found in the smalt- and lapis lazuli-based tempera, in addition to the physical-chemical damage to the binders. The information reported here would be useful for preventive conservation, as well as for art restorers, who are planning work on paintings in which paints of this kind were used. |
| first_indexed | 2024-03-10T19:55:07Z |
| format | Article |
| id | doaj.art-09a1fd0d1b8048eb8b3aabf1ea28ab38 |
| institution | Directory Open Access Journal |
| issn | 2075-163X |
| language | English |
| last_indexed | 2024-03-10T19:55:07Z |
| publishDate | 2020-05-01 |
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| series | Minerals |
| spelling | doaj.art-09a1fd0d1b8048eb8b3aabf1ea28ab382023-11-19T23:58:53ZengMDPI AGMinerals2075-163X2020-05-0110542710.3390/min10050427Effect of a SO<sub>2</sub> Rich Atmosphere on Tempera Paint Mock-Ups. Part 1: Accelerated Aging of Smalt and Lapis Lazuli-Based PaintsJosé Santiago Pozo-Antonio0Teresa Rivas1Amelia Dionísio2Diana Barral3Carolina Cardell4Dpto. de Enxeñaría de Recursos Naturais e Medio Ambiente, Universidade de Enxeñaría de Minas e Enerxía, Universidade de Vigo, 36310 Vigo, SpainDpto. de Enxeñaría de Recursos Naturais e Medio Ambiente, Universidade de Enxeñaría de Minas e Enerxía, Universidade de Vigo, 36310 Vigo, SpainCERENA, Instituto Superior Técnico, Universidade de Lisboa. Av. Rovisco Pais, 1049-001 Lisboa, PortugalDpto. de Enxeñaría de Recursos Naturais e Medio Ambiente, Universidade de Enxeñaría de Minas e Enerxía, Universidade de Vigo, 36310 Vigo, SpainDepartment of Mineralogy and Petrology, Faculty of Science, University of Granada, 18071 Granada, SpainThe behavior of historic tempera paints exposed to pollutant gases is an important issue when developing conservation strategies. In this work, binary tempera paint mock-ups that were made with either smalt or lapis lazuli pigments mixed with either rabbit glue or egg yolk binders were exposed to an SO<sub>2</sub> accelerated aging test in order to find out more about the forms and mechanisms of alteration resulting from pigment-binder interaction. To this end, spectrophotometry, hyperspectral image analysis, and profilometry were used to study macro-scale, physical changes taking place on the surface of the paints, affecting color, gloss, reflectance, and roughness. Likewise, chemical and mineralogical changes were evaluated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (ATR-FTIR), polarized light microscopy (PLM), and scanning electron microscopy with micro-analysis (SEM-EDS), which was also used to visualize micro-texture changes in the paints. The smalt-based tempera showed a higher degree of deterioration than the lapis lazuli-based tempera, in particular a notable whitening related to the precipitation of sulfate-rich salts and to binder and pigment chemical alterations. Moreover, whereas aged egg yolk-based paints showed visible color change due to damage to the oily binder and the pigments, the most evident change in rabbit glue-based paints was binder loss. The alteration suffered by the pigments varied in line with their composition; thus, smalt (blue cobalt-containing glass) grains were more sensitive to SO<sub>2</sub> exposure than lapis lazuli-(Na,Ca)<sub>8</sub>[(S,Cl,SO<sub>4</sub>,OH)<sub>2</sub>|(Al<sub>6</sub>Si<sub>6</sub>O<sub>24</sub>)]-crystals. In the smalt grains, the SO<sub>2</sub> test caused K<sup>+</sup> leaching from the glass matrix, which was detected by means of K/Co ratios, but the lazurite crystals (main component of lapis lazuli) were unaffected (regardless of the binder used in the tempera). The most likely source of the crystallized sulfate rich salts were the impurities that were detected in association with the natural lapis lazuli pigment, i.e., calcite and diopside. Indeed, the precipitation of efflorescences is the main cause of the optical changes found in the smalt- and lapis lazuli-based tempera, in addition to the physical-chemical damage to the binders. The information reported here would be useful for preventive conservation, as well as for art restorers, who are planning work on paintings in which paints of this kind were used.https://www.mdpi.com/2075-163X/10/5/427tempera paintinorganic pigmentproteinaceous bindersulfur dioxidephysical-chemical changesulfate-rich salt |
| spellingShingle | José Santiago Pozo-Antonio Teresa Rivas Amelia Dionísio Diana Barral Carolina Cardell Effect of a SO<sub>2</sub> Rich Atmosphere on Tempera Paint Mock-Ups. Part 1: Accelerated Aging of Smalt and Lapis Lazuli-Based Paints Minerals tempera paint inorganic pigment proteinaceous binder sulfur dioxide physical-chemical change sulfate-rich salt |
| title | Effect of a SO<sub>2</sub> Rich Atmosphere on Tempera Paint Mock-Ups. Part 1: Accelerated Aging of Smalt and Lapis Lazuli-Based Paints |
| title_full | Effect of a SO<sub>2</sub> Rich Atmosphere on Tempera Paint Mock-Ups. Part 1: Accelerated Aging of Smalt and Lapis Lazuli-Based Paints |
| title_fullStr | Effect of a SO<sub>2</sub> Rich Atmosphere on Tempera Paint Mock-Ups. Part 1: Accelerated Aging of Smalt and Lapis Lazuli-Based Paints |
| title_full_unstemmed | Effect of a SO<sub>2</sub> Rich Atmosphere on Tempera Paint Mock-Ups. Part 1: Accelerated Aging of Smalt and Lapis Lazuli-Based Paints |
| title_short | Effect of a SO<sub>2</sub> Rich Atmosphere on Tempera Paint Mock-Ups. Part 1: Accelerated Aging of Smalt and Lapis Lazuli-Based Paints |
| title_sort | effect of a so sub 2 sub rich atmosphere on tempera paint mock ups part 1 accelerated aging of smalt and lapis lazuli based paints |
| topic | tempera paint inorganic pigment proteinaceous binder sulfur dioxide physical-chemical change sulfate-rich salt |
| url | https://www.mdpi.com/2075-163X/10/5/427 |
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