New Insights into Synthetic Copper Greens: The Search for Specific Signatures by Raman and Infrared Spectroscopy for Their Characterization in Medieval Artworks
Abstract
:1. Introduction
1.1. Medieval Copper Greens
1.2. The Synthesis of Cu(CH3COO)2·H2O Using Copper in the Presence of Acetic Acid
4Cu + O2 → 2Cu2O | (1) redox reaction |
Cu2O + 4CH3COOH → 2Cu(CH3COO) 2·H2O | (2) redox reaction (O2 as oxidant) and ligand exchange |
1.3. Characterizing Verdigris and Other Copper Patinas by Raman Spectroscopy
1.4. Characterizing Verdigris and Other Copper Patinas by Infrared Spectroscopy
2. Experimental
2.1. Materials
2.1.1. Reference Materials
2.1.2. Ingredients
2.2. Preparation of Medieval Copper Greens
2.3. Equipment and Characterization Methods
2.3.1. Raman Microscopy (μRaman)
2.3.2. Fourier Transform Infrared Microspectroscopy (μFTIR)
2.3.3. Micro-Energy Dispersive X-ray Fluorescence (μ-EDXRF)
2.3.4. X-Ray Diffraction (XRD)
3. Results and Discussion
3.1. Characterization of the Synthesized Pigments
3.2. Detailed Characterization of Groups 1 and 2
3.3. Detailed Characterization of Group 3
3.4. Oxalates as Degradation Products or Markers of Specific Recipes?
4. Conclusions
Supplementary Materials
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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1 | In a recipe using brass in an oak box, we also detected the presence of zinc acetate, in agreement with the literature [17]. |
Reaction Vessel | Group 1 | Group 2 § | Group 3 | Group 4 | Group 5 | |
---|---|---|---|---|---|---|
Cu(CH3COO)2·H2O | Cu(CH3COO)2·H2O CuC2O4·nH2O | Cu(CH3COO)2·H2O Cu2(OH)3Cl CuCl | miscellaneous | no products | ||
glass vessel | | 6 | 6 | 1 | 2 | 11 |
13.6% | 13.6% | 2.3% | 4.5% | 25% | ||
oak box | | 7 | 3 | 5 | 1 | 2 |
15.9% | 6.8% | 11.4% | 2.3% | 4.5% |
Copper Acetate | Copper Oxalate | Basic Copper Chloride | Copper(II) Oxide | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Cu(CH3COO)2·H2O | CuC2O4·nH2O | Cu2(OH)3Cl | Cu2O | ||||||||
231 | m | ν(CuO) | 209 | m | ν(CuO) | 119 | w | 218 | vs | ν(CuO) | |
322 | vs | 556 | vs | 147 | w | δ(OCuO) | 418 | w | |||
703 | m | δ(OCO) | 585, 610 | sh | 513 | w | ν(CuO) | 630 | w | ||
948 | s | ν(CC) | 831 | m | δ(OCO) | 911 | w | δ(CuOH) | |||
1418 | sh | δ(CH3) | 924 | m | ν(CC) | 3329 | w | ν(OH) | |||
1440 | m | ν(COO−) | 1486 | sh | ν(CO) | 3350 | m | ||||
2941 | s | ν(CH) | 1518 | s | 3435 | vs | |||||
2989, 3024 | sh | 1615 | w |
Copper Acetate | Copper Oxalate | Basic Copper Chloride | ||||||
---|---|---|---|---|---|---|---|---|
Cu(CH3COO)2·H2O | CuC2O4·nH2O | Cu2(OH)3Cl | ||||||
629 | m | δ(COO−) | 824 | m | ν(CC) | 849 | w | |
692 | m | δ(COO−) | 1320 | s | νs(COO−)/ | 894 | w | |
1033 | w | δ(CH3) | 1364 | s | δ(OCO) | 949 | w | δ(OH) |
1052 | w | δ(CH3) | 1677 | vs | νa(COO−) | 986 | w | |
1445 | s | δ(CH3) | 1655 | w | ||||
1602 | vs | ν(COO−) | 3341 | vs | ν(OH) | |||
3475, 3375, 3272 | m | ν(OH) | 3443 | sh |
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Buse, J.; Otero, V.; Melo, M.J. New Insights into Synthetic Copper Greens: The Search for Specific Signatures by Raman and Infrared Spectroscopy for Their Characterization in Medieval Artworks. Heritage 2019, 2, 1614-1629. https://doi.org/10.3390/heritage2020099
Buse J, Otero V, Melo MJ. New Insights into Synthetic Copper Greens: The Search for Specific Signatures by Raman and Infrared Spectroscopy for Their Characterization in Medieval Artworks. Heritage. 2019; 2(2):1614-1629. https://doi.org/10.3390/heritage2020099
Chicago/Turabian StyleBuse, Juliana, Vanessa Otero, and Maria J. Melo. 2019. "New Insights into Synthetic Copper Greens: The Search for Specific Signatures by Raman and Infrared Spectroscopy for Their Characterization in Medieval Artworks" Heritage 2, no. 2: 1614-1629. https://doi.org/10.3390/heritage2020099