The discrimination of synthetic and natural red ochres is an intriguing topic, being the synthesis of these pigments probably known since Prehistory[1,2]. The present work is a systematic study to define the best, less invasive methodology in the discrimination of synthetic and natural red ochres. After the laboratory synthesis of Mars yellow and the collection of commercial or museum samples, all yellow samples were heated following two different pathways to obtain synthetic red ochres. The sample-set has been characterized by different analytical techniques: X-ray powder diffraction (XRPD), scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), thermal analysis and Fourier transform infrared spectroscopy (μ-FTIR). The synthetic pathway was also reproduced and followed through differential thermal analysis (DTA and TG). This multi-analytical approach was set to understand which technique – or a combination of more than one – has higher efficiency in the distinction of synthetic and natural red ochres. XRD remarked the different origin of precursory samples. SEM-EDS showed typical morphological features of Mars yellow that are partially retained even after heating, leading to the recognition of both Mars pigments. DTA and TG highlighted that the process sensibly differs from Mars yellow to natural ochres. Mars yellow is in fact characterized by a double-peak with minima at 551 and 577 K, while dehydration is a single-step process in natural ochres. Finally, μ-FTIR proved to be very effective to discriminate a soft heating from the hard one. In particular, hydroxyl and FeO6 bands in the fingerprint region were the most useful for the task. Distinctive features of Mars products were for the first time characterized thanks to this combined methodology. [1] Helwig K. (2014): in Artists’ pigments: a handbook of their history and characteristics, 4. National Galleryof Art and Archetype Publications. [2] Salomon H. et al. (2015), J. Archaeol. Sci. 55, 100.
New insights on the discrimination of synthesized ochres by μ-FTIR: Mars yellow and calcinated red ochres recognition criteria / Botticelli, M.; Candeias, A.; Maras, A.. - (2019). (Intervento presentato al convegno 9th European Conference on Mineralogy and Spectroscopy tenutosi a Prague, Czech Republic).
New insights on the discrimination of synthesized ochres by μ-FTIR: Mars yellow and calcinated red ochres recognition criteria
M. Botticelli
;A. Maras
2019
Abstract
The discrimination of synthetic and natural red ochres is an intriguing topic, being the synthesis of these pigments probably known since Prehistory[1,2]. The present work is a systematic study to define the best, less invasive methodology in the discrimination of synthetic and natural red ochres. After the laboratory synthesis of Mars yellow and the collection of commercial or museum samples, all yellow samples were heated following two different pathways to obtain synthetic red ochres. The sample-set has been characterized by different analytical techniques: X-ray powder diffraction (XRPD), scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), thermal analysis and Fourier transform infrared spectroscopy (μ-FTIR). The synthetic pathway was also reproduced and followed through differential thermal analysis (DTA and TG). This multi-analytical approach was set to understand which technique – or a combination of more than one – has higher efficiency in the distinction of synthetic and natural red ochres. XRD remarked the different origin of precursory samples. SEM-EDS showed typical morphological features of Mars yellow that are partially retained even after heating, leading to the recognition of both Mars pigments. DTA and TG highlighted that the process sensibly differs from Mars yellow to natural ochres. Mars yellow is in fact characterized by a double-peak with minima at 551 and 577 K, while dehydration is a single-step process in natural ochres. Finally, μ-FTIR proved to be very effective to discriminate a soft heating from the hard one. In particular, hydroxyl and FeO6 bands in the fingerprint region were the most useful for the task. Distinctive features of Mars products were for the first time characterized thanks to this combined methodology. [1] Helwig K. (2014): in Artists’ pigments: a handbook of their history and characteristics, 4. National Galleryof Art and Archetype Publications. [2] Salomon H. et al. (2015), J. Archaeol. Sci. 55, 100.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
