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Regina N. Tempel - One of the best experts on this subject based on the ideXlab platform.
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Geochemical modeling of arsenic sulfide oxidation kinetics in a mining environment
Geochimica et Cosmochimica Acta, 2005Co-Authors: Maggy F. Lengke, Regina N. TempelAbstract:Abstract Arsenic sulfide (AsS (am), As2S3 (am), Orpiment, and realgar) oxidation rates increase with increasing pH values. The rates of arsenic sulfide oxidation at higher pH values relative to those at pH∼2 are in the range of 26–4478, 3–17, 8–182, and 4–10 times for As2S3 (am), Orpiment, AsS (am), and realgar, respectively. Numerical simulations of Orpiment and realgar oxidation kinetics were conducted using the geochemical reaction path code EQ3/6 to evaluate the effects of variable DO concentrations and mineral reactivity factors on water chemistry evolution during Orpiment and realgar oxidation. The results show that total As concentrations increase by ∼1.14 to 13 times and that pH values decrease by ∼0.6 to 4.2 U over a range of mineral reactivity factors from 1% to 50% after 2000 days (5.5 yr). The As release from Orpiment and realgar oxidation exceeds the current U.S. National Drinking Water Standard (0.05 ppm) approximately in 200–300 days at the lowest initial dissolved oxygen concentration (3 ppm) and a reactivity factor of 1%. The results of simulations of Orpiment oxidation in the presence of albite and calcite show that calcite can act as an effective buffer to the acid water produced from Orpiment oxidation within relatively short periods (days/months), but the release of As continues to increase. Pyrite oxidation rates are faster than Orpiment and realgar from pH 2.3 to 8; however, pyrite oxidation rates are slower than As2S3 (am) and AsS (am) at pH 8. The activation energies of arsenic sulfide oxidation range from 16 to 124 kJ/mol at pH∼8 and temperature 25 to 40°C, and pyrite activation energies are ∼52 to 88 kJ/mol, depending on pH and temperature range. The magnitude of activation energies for both pyrite and arsenic sulfide solids indicates that the oxidation of these minerals is dominated by surface reactions, except for As2S3 (am). Low activation energies of As2S3 (am) indicate that diffusion may be rate controlling. Limestone is commonly mixed with sulfide minerals in a mining environment to prevent acid water formation. However, the oxidation rates of arsenic sulfides increase as solution pH rises and result in a greater release of As. Furthermore, the lifetimes of carbonate minerals (i.e., calcite, aragonite, and dolomite) are much shorter than those of arsenic sulfide and silicate minerals. Thus, within a geologic frame time, carbonate minerals may not be present to act as a pH buffer for acid mine waters. Additionally, the presence of silicate minerals such as pyroxenes (wollastonite, jadeite, and spodumene) and Ca-feldspars (labradorite, anorthite, and nepheline) may not be important for buffering acid solutions because these minerals dissolve faster than and have shorter lifetimes than sulfide minerals. However, other silicate minerals such as Na and K-feldspars (albite, sanidine, and microcline), quartz, pyroxenes (augite, enstatite, diopsite, and MnSiO3) that have much longer lifetimes than arsenic sulfide minerals may be present in a system. The results of our modeling of arsenic sulfide mineral oxidation show that these minerals potentially can release significant concentrations of dissolved As to natural waters, and the factors and mechanisms involved in arsenic sulfide oxidation warrant further study.
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reaction rates of natural Orpiment oxidation at 25 to 40 c and ph 6 8 to 8 2 and comparison with amorphous as2s3 oxidation
Geochimica et Cosmochimica Acta, 2002Co-Authors: Maggy F. Lengke, Regina N. TempelAbstract:The oxidation rate of natural Orpiment from Carlin-type deposits was measured at 25 to 40°C in a mixed flow reactor as a function of pH (6.8 to 8.2) and dissolved oxygen concentration (6.4 to 17.4 ppm) with a starting ionic strength of 0.01 M NaCl. All experiments ran for approximately 30 h, where steady-state conditions were reached after 20 h at a flow rate of 10 mL/min. The stoichiometric ratio of As/S was observed once steady state was reached. The rate law of Orpiment oxidation is as follows: where R signifies the rate of Orpiment destruction (mol m−2 s−1), [DO] is the concentration of dissolved oxygen (M), and [H+] is the concentration of proton (M). The activation energy for the Orpiment oxidation by dissolved oxygen at a temperature range of 25 to 40°C is 59.1 kJ/mol. Oxidation reactions of Orpiment show incomplete oxidation of arsenic and sulfide in solution. At a pH range of 6.8 to 8.2, As(III) exists as H3AsO3 and As(V) is present as HAsO42− and H2AsO4−. Sulfite, sulfate, and thiosulfate are present as small fractions of total sulfur. The possible major sulfur species are intermediate oxidation state species. The oxidation rate of natural Orpiment oxidation is slightly lower by a factor of 0.002 to 0.560 than that of As2S3(am) at the considered pH 7 to 10 and DO concentrations of 1 to 10 ppm. The dependence factors on pH for natural Orpiment oxidation are lower by a factor of 0.37 compared with As2S3(am). However, the calculated activation energy is much larger for natural Orpiment than As2S3(am) by a factor of 3.5. As(III) and As(V) are the major products for both As2S3(am) and natural Orpiment oxidation along with intermediate sulfur species. The rate of Orpiment oxidation increases with pH and results in an increase in the release of As. In mining-impacted environments with alkaline waters, as may be found in carbonate-hosted ore deposits, the natural attenuation of As oxyanions by sorption to oxide/hydroxide mineral surfaces is minimized because of a negative surface charge at a higher pH range. Thus, As concentrations may increase in mining-impacted waters at higher pH values (>8).
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Reaction rates of natural Orpiment oxidation at 25 to 40°C and pH 6.8 to 8.2 and comparison with amorphous As2S3 oxidation
Geochimica et Cosmochimica Acta, 2002Co-Authors: Maggy F. Lengke, Regina N. TempelAbstract:The oxidation rate of natural Orpiment from Carlin-type deposits was measured at 25 to 40°C in a mixed flow reactor as a function of pH (6.8 to 8.2) and dissolved oxygen concentration (6.4 to 17.4 ppm) with a starting ionic strength of 0.01 M NaCl. All experiments ran for approximately 30 h, where steady-state conditions were reached after 20 h at a flow rate of 10 mL/min. The stoichiometric ratio of As/S was observed once steady state was reached. The rate law of Orpiment oxidation is as follows: where R signifies the rate of Orpiment destruction (mol m−2 s−1), [DO] is the concentration of dissolved oxygen (M), and [H+] is the concentration of proton (M). The activation energy for the Orpiment oxidation by dissolved oxygen at a temperature range of 25 to 40°C is 59.1 kJ/mol. Oxidation reactions of Orpiment show incomplete oxidation of arsenic and sulfide in solution. At a pH range of 6.8 to 8.2, As(III) exists as H3AsO3 and As(V) is present as HAsO42− and H2AsO4−. Sulfite, sulfate, and thiosulfate are present as small fractions of total sulfur. The possible major sulfur species are intermediate oxidation state species. The oxidation rate of natural Orpiment oxidation is slightly lower by a factor of 0.002 to 0.560 than that of As2S3(am) at the considered pH 7 to 10 and DO concentrations of 1 to 10 ppm. The dependence factors on pH for natural Orpiment oxidation are lower by a factor of 0.37 compared with As2S3(am). However, the calculated activation energy is much larger for natural Orpiment than As2S3(am) by a factor of 3.5. As(III) and As(V) are the major products for both As2S3(am) and natural Orpiment oxidation along with intermediate sulfur species. The rate of Orpiment oxidation increases with pH and results in an increase in the release of As. In mining-impacted environments with alkaline waters, as may be found in carbonate-hosted ore deposits, the natural attenuation of As oxyanions by sorption to oxide/hydroxide mineral surfaces is minimized because of a negative surface charge at a higher pH range. Thus, As concentrations may increase in mining-impacted waters at higher pH values (>8).
Maggy F. Lengke - One of the best experts on this subject based on the ideXlab platform.
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Geochemical modeling of arsenic sulfide oxidation kinetics in a mining environment
Geochimica et Cosmochimica Acta, 2005Co-Authors: Maggy F. Lengke, Regina N. TempelAbstract:Abstract Arsenic sulfide (AsS (am), As2S3 (am), Orpiment, and realgar) oxidation rates increase with increasing pH values. The rates of arsenic sulfide oxidation at higher pH values relative to those at pH∼2 are in the range of 26–4478, 3–17, 8–182, and 4–10 times for As2S3 (am), Orpiment, AsS (am), and realgar, respectively. Numerical simulations of Orpiment and realgar oxidation kinetics were conducted using the geochemical reaction path code EQ3/6 to evaluate the effects of variable DO concentrations and mineral reactivity factors on water chemistry evolution during Orpiment and realgar oxidation. The results show that total As concentrations increase by ∼1.14 to 13 times and that pH values decrease by ∼0.6 to 4.2 U over a range of mineral reactivity factors from 1% to 50% after 2000 days (5.5 yr). The As release from Orpiment and realgar oxidation exceeds the current U.S. National Drinking Water Standard (0.05 ppm) approximately in 200–300 days at the lowest initial dissolved oxygen concentration (3 ppm) and a reactivity factor of 1%. The results of simulations of Orpiment oxidation in the presence of albite and calcite show that calcite can act as an effective buffer to the acid water produced from Orpiment oxidation within relatively short periods (days/months), but the release of As continues to increase. Pyrite oxidation rates are faster than Orpiment and realgar from pH 2.3 to 8; however, pyrite oxidation rates are slower than As2S3 (am) and AsS (am) at pH 8. The activation energies of arsenic sulfide oxidation range from 16 to 124 kJ/mol at pH∼8 and temperature 25 to 40°C, and pyrite activation energies are ∼52 to 88 kJ/mol, depending on pH and temperature range. The magnitude of activation energies for both pyrite and arsenic sulfide solids indicates that the oxidation of these minerals is dominated by surface reactions, except for As2S3 (am). Low activation energies of As2S3 (am) indicate that diffusion may be rate controlling. Limestone is commonly mixed with sulfide minerals in a mining environment to prevent acid water formation. However, the oxidation rates of arsenic sulfides increase as solution pH rises and result in a greater release of As. Furthermore, the lifetimes of carbonate minerals (i.e., calcite, aragonite, and dolomite) are much shorter than those of arsenic sulfide and silicate minerals. Thus, within a geologic frame time, carbonate minerals may not be present to act as a pH buffer for acid mine waters. Additionally, the presence of silicate minerals such as pyroxenes (wollastonite, jadeite, and spodumene) and Ca-feldspars (labradorite, anorthite, and nepheline) may not be important for buffering acid solutions because these minerals dissolve faster than and have shorter lifetimes than sulfide minerals. However, other silicate minerals such as Na and K-feldspars (albite, sanidine, and microcline), quartz, pyroxenes (augite, enstatite, diopsite, and MnSiO3) that have much longer lifetimes than arsenic sulfide minerals may be present in a system. The results of our modeling of arsenic sulfide mineral oxidation show that these minerals potentially can release significant concentrations of dissolved As to natural waters, and the factors and mechanisms involved in arsenic sulfide oxidation warrant further study.
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reaction rates of natural Orpiment oxidation at 25 to 40 c and ph 6 8 to 8 2 and comparison with amorphous as2s3 oxidation
Geochimica et Cosmochimica Acta, 2002Co-Authors: Maggy F. Lengke, Regina N. TempelAbstract:The oxidation rate of natural Orpiment from Carlin-type deposits was measured at 25 to 40°C in a mixed flow reactor as a function of pH (6.8 to 8.2) and dissolved oxygen concentration (6.4 to 17.4 ppm) with a starting ionic strength of 0.01 M NaCl. All experiments ran for approximately 30 h, where steady-state conditions were reached after 20 h at a flow rate of 10 mL/min. The stoichiometric ratio of As/S was observed once steady state was reached. The rate law of Orpiment oxidation is as follows: where R signifies the rate of Orpiment destruction (mol m−2 s−1), [DO] is the concentration of dissolved oxygen (M), and [H+] is the concentration of proton (M). The activation energy for the Orpiment oxidation by dissolved oxygen at a temperature range of 25 to 40°C is 59.1 kJ/mol. Oxidation reactions of Orpiment show incomplete oxidation of arsenic and sulfide in solution. At a pH range of 6.8 to 8.2, As(III) exists as H3AsO3 and As(V) is present as HAsO42− and H2AsO4−. Sulfite, sulfate, and thiosulfate are present as small fractions of total sulfur. The possible major sulfur species are intermediate oxidation state species. The oxidation rate of natural Orpiment oxidation is slightly lower by a factor of 0.002 to 0.560 than that of As2S3(am) at the considered pH 7 to 10 and DO concentrations of 1 to 10 ppm. The dependence factors on pH for natural Orpiment oxidation are lower by a factor of 0.37 compared with As2S3(am). However, the calculated activation energy is much larger for natural Orpiment than As2S3(am) by a factor of 3.5. As(III) and As(V) are the major products for both As2S3(am) and natural Orpiment oxidation along with intermediate sulfur species. The rate of Orpiment oxidation increases with pH and results in an increase in the release of As. In mining-impacted environments with alkaline waters, as may be found in carbonate-hosted ore deposits, the natural attenuation of As oxyanions by sorption to oxide/hydroxide mineral surfaces is minimized because of a negative surface charge at a higher pH range. Thus, As concentrations may increase in mining-impacted waters at higher pH values (>8).
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Reaction rates of natural Orpiment oxidation at 25 to 40°C and pH 6.8 to 8.2 and comparison with amorphous As2S3 oxidation
Geochimica et Cosmochimica Acta, 2002Co-Authors: Maggy F. Lengke, Regina N. TempelAbstract:The oxidation rate of natural Orpiment from Carlin-type deposits was measured at 25 to 40°C in a mixed flow reactor as a function of pH (6.8 to 8.2) and dissolved oxygen concentration (6.4 to 17.4 ppm) with a starting ionic strength of 0.01 M NaCl. All experiments ran for approximately 30 h, where steady-state conditions were reached after 20 h at a flow rate of 10 mL/min. The stoichiometric ratio of As/S was observed once steady state was reached. The rate law of Orpiment oxidation is as follows: where R signifies the rate of Orpiment destruction (mol m−2 s−1), [DO] is the concentration of dissolved oxygen (M), and [H+] is the concentration of proton (M). The activation energy for the Orpiment oxidation by dissolved oxygen at a temperature range of 25 to 40°C is 59.1 kJ/mol. Oxidation reactions of Orpiment show incomplete oxidation of arsenic and sulfide in solution. At a pH range of 6.8 to 8.2, As(III) exists as H3AsO3 and As(V) is present as HAsO42− and H2AsO4−. Sulfite, sulfate, and thiosulfate are present as small fractions of total sulfur. The possible major sulfur species are intermediate oxidation state species. The oxidation rate of natural Orpiment oxidation is slightly lower by a factor of 0.002 to 0.560 than that of As2S3(am) at the considered pH 7 to 10 and DO concentrations of 1 to 10 ppm. The dependence factors on pH for natural Orpiment oxidation are lower by a factor of 0.37 compared with As2S3(am). However, the calculated activation energy is much larger for natural Orpiment than As2S3(am) by a factor of 3.5. As(III) and As(V) are the major products for both As2S3(am) and natural Orpiment oxidation along with intermediate sulfur species. The rate of Orpiment oxidation increases with pH and results in an increase in the release of As. In mining-impacted environments with alkaline waters, as may be found in carbonate-hosted ore deposits, the natural attenuation of As oxyanions by sorption to oxide/hydroxide mineral surfaces is minimized because of a negative surface charge at a higher pH range. Thus, As concentrations may increase in mining-impacted waters at higher pH values (>8).
Koen Janssens - One of the best experts on this subject based on the ideXlab platform.
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Combined Micro- and Macro scale X-ray powder diffraction mapping of degraded Orpiment paint in a 17th century still life painting by Martinus Nellius
Heritage Science, 2019Co-Authors: Jonas Simoen, Geert Van Der Snickt, Steven De Meyer, Frederik Vanmeert, Nouchka Keyser, Ermanno Avranovich, Annelies Loon, Katrien Keune, Koen JanssensAbstract:The spontaneous chemical alteration of artists’ pigment materials may be caused by several degradation processes. Some of these are well known while others are still in need of more detailed investigation and documentation. These changes often become apparent as color modifications, either caused by a change in the oxidation state in the original material or the formation of degradation products or salts, via simple or more complex, multistep reactions. Arsenic-based pigments such as Orpiment (As_2S_3) or realgar (α-As_4S_4) are prone to such alterations and are often described as easily oxidizing upon exposure to light. Macroscopic X-ray powder diffraction (MA-XRPD) imaging on a sub area of a still life painting by the 17th century Dutch painter Martinus Nellius was employed in combination with microscopic (μ-) XRPD imaging of a paint cross section taken in the area imaged by MA-XRPD. In this way, the in situ formation of secondary metal arsenate and sulfate species and their migration through the paint layer stack they originate from could be visualized. In the areas originally painted with Orpiment, it could be shown that several secondary minerals such as schultenite (PbHAsO_4), mimetite (Pb_5(AsO_4)_3Cl), palmierite (K_2Pb(SO_4)_2) and syngenite (K_2Ca(SO_4)_2∙H_2O) have formed. Closer inspection of the cross-sectioned paint layer stack with μ-XRPD illustrates that the arsenate minerals schultenite and mimetite have precipitated at the interface between the Orpiment layer and the layer below that is rich in lead white, i.e. close to the depth of formation of the arsenate ions. The sulfate palmierite has mostly precipitated at the surface and upper layers of the painting.
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Artificial Orpiment, a new pigment in Rembrandt’s palette
Heritage Science, 2017Co-Authors: Annelies Van Loon, Petria Noble, Anna Krekeler, Yoshinari Abe, Izumi Nakai, Koen Janssens, Geert Van Der Snickt, Joris DikAbstract:This paper reports on how the application of macro X-ray fluorescence (MA-XRF) imaging, in combination with the re-examination of existing paint cross-sections, has led to the discovery of a new pigment in Rembrandt’s palette: artificial Orpiment. In the NWO Science4Arts ‘ReVisRembrandt’ project, novel chemical imaging techniques are being developed and applied to the study of Rembrandt’s late paintings in order to help resolve outstanding questions and to gain a better understanding of his late enigmatic painting technique. One of the selected case studies is the Portrait of a Couple as Isaac and Rebecca, known as ‘The Jewish Bride’, dated c. 1665 and on view in the Rijksmuseum. During the re-installation of the Rijksmuseum in 2013, the picture was scanned using the Bruker M6 Jetstream MA-XRF scanner. The resulting elemental distribution maps made it possible to distinguish many features in the painting, such as bone black remains of the original hat (P, Ca maps), and the now discolored smalt-rich background (Co, Ni, As, K maps). The arsenic (As) map also revealed areas of high-intensity in Isaac’s sleeve and Rebecca’s dress where it could be established that it was not related with the pigment smalt that also contains arsenic. This pointed to the presence of a yellow or orange arsenic-containing pigment, such as realgar or Orpiment that is not associated with the artist’s palette. Subsequent examination of existing paint cross-sections from these locations taken by Karin Groen in the 1990s identified isolated, almost perfectly round particles of arsenic sulfide. The round shape corresponds with published findings on a purified form of artificial Orpiment glass obtained by dry processing, a sublimation reaction. In bright field, the particles characteristically exhibit a dark cross in the middle caused by internal light reflections. The results of additional non-invasive techniques (portable XRD and portable Raman) are discussed, as well as the implications of this finding and how it fits with Rembrandt’s late experimental painting technique.
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Artificial Orpiment, a new pigment in Rembrandt's palette
Heritage Science, 2017Co-Authors: Annelies Van Loon, Petria Noble, Anna Krekeler, Yoshinari Abe, Izumi Nakai, Geert Van Der Snickt, Koen Janssens, Joris DikAbstract:This paper reports on how the application of macro X-ray fluorescence (MA-XRF) imaging, in combination with the re-examination of existing paint cross-sections, has led to the discovery of a new pigment in Rembrandt’s palette: artificial Orpiment. In the NWO Science4Arts ‘ReVisRembrandt’ project, novel chemical imaging techniques are being developed and applied to the study of Rembrandt’s late paintings in order to help resolve outstanding questions and to gain a better understanding of his late enigmatic painting technique. One of the selected case studies is the Portrait of a Couple as Isaac and Rebecca, known as ‘The Jewish Bride’, dated c. 1665 and on view in the Rijksmuseum. During the re-installation of the Rijksmuseum in 2013, the picture was scanned using the Bruker M6 Jetstream MA-XRF scanner. The resulting elemental distribution maps made it possible to distinguish many features in the painting, such as bone black remains of the original hat (P, Ca maps), and the now discolored smalt-rich background (Co, Ni, As, K maps). The arsenic (As) map also revealed areas of high-intensity in Isaac’s sleeve and Rebecca’s dress where it could be established that it was not related with the pigment smalt that also contains arsenic. This pointed to the presence of a yellow or orange arsenic-containing pigment, such as realgar or Orpiment that is not associated with the artist’s palette. Subsequent examination of existing paint cross-sections from these locations taken by Karin Groen in the 1990s identified isolated, almost perfectly round particles of arsenic sulfide. The round shape corresponds with published findings on a purified form of artificial Orpiment glass obtained by dry processing, a sublimation reaction. In bright field, the particles characteristically exhibit a dark cross in the middle caused by internal light reflections. The results of additional non-invasive techniques (portable XRD and portable Raman) are discussed, as well as the implications of this finding and how it fits with Rembrandt’s late experimental painting technique.
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The darkening of copper- or lead-based pigments explained by a structural modification of natural Orpiment : a spectroscopic and electrochemical study
Journal of Analytical Atomic Spectrometry, 2017Co-Authors: Marc Vermeulen, Koen Janssens, Jana Sanyova, Gert Nuyts, Steven De Meyer, Karolien De WaelAbstract:A combined Raman and electrochemical study of natural Orpiment (As2S3), an arsenic sulfide pigment, was used to assess the quick formation of oxidized species such as arsenic oxide (As2O3) upon exposing the pigment to 405 nm or 532 nm monochromatic light while simultaneously recording the Raman spectra of the exposed sample. During this process, a distortion of the main band at 355 cm−1, associated with the stretching of the AsS3/2 pyramids of natural Orpiment, was observed as well as an increased intensity of the 359 cm−1 band, corresponding to covalent As–As bonds in natural Orpiment. The distortion was accompanied by an overall decrease of the global Raman signal for natural Orpiment, which could be explained by a loss in the crystal structure. The same phenomena were recorded in reference natural Orpiment model paint samples stored for a long time together with verdigris (Cu(OH)2·(CH3COO)2·5H2O) and minium (Pb3O4) paints, the latter two appearing darkened on their sides closest to the Orpiment sample as well as in several historical samples containing natural Orpiment mixed with various blue pigments. By SEM-EDX and XRPD analysis, respectively on loose material and cast thin-sections of model paint samples, the darkening was identified as dark sulfide species such as chalcocite (Cu2S) and galena (PbS), suggesting the release of volatile sulfide or related species by the natural Orpiment paint. XANES analyses of paint samples presenting As–As bond increase indicated the presence of sulfur species most likely identified as organosulfur compounds formed upon the As–As bond formation and explained the darkening of the Cu- and Pb-based pigments. To the best of our knowledge, this article reports for the first time the light-induced formation of As–As bonds in natural Orpiment used as an artists' pigment and objectively demonstrates the incompatibility between Orpiment and (arsenic) sulfide-sensitive pigments.
Jörg Göttlicher - One of the best experts on this subject based on the ideXlab platform.
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Amorphous As-sulfide precipitates from the shallow-water hydrothermal vents off Milos Island (Greece)
Marine Chemistry, 2015Co-Authors: Athanasios Godelitsas, Roy E. Price, Thomas Pichler, Jan P. Amend, P. Gamaletsos, Jörg GöttlicherAbstract:Abstract Amorphous Orpiment-like As-sulfides (As 2 S 3 ) are the most common As phases precipitating in hydrothermal systems, yet there is a lack of information regarding their solid-state characterization. Using a combination of optical, SEM–EDS, micro-Raman and XANES/EXAFS applications, we investigated yellow-orange As- and S-rich sediments occurring in the shallow-water hydrothermal system off the coast of Milos Island, Greece. The precipitates have several morphologies, but are dominantly colloidal. Intriguing “biological” morphologies also exist (e.g., cell-like (~ 10 μm), spirals (~ 20 μm), and rounded “cinnamon bun” shapes (~ 20 μm)). SEM–EDS data indicated that the precipitates have an As:S ratio similar to Orpiment (average = 0.58, range 0.51–0.63; n = 8). Micro-Raman spectra indicated that orange colored precipitates appear to be dominated by poorly crystalline and/or amorphous arsenic sulfides with micro-amounts of more crystalline Orpiment and impure sulfur. The yellow sediments also contained crystalline elemental sulfur in the form S 8 . Bulk As K -edge XANES spectra of the As-sulfide precipitates proved a valence of As corresponding to Orpiment-type (As 2 S 3 ) compounds (− 1 to + 3). EXAFS fitting results indicated that the studied material exhibits an amorphous Orpiment-like structure with As ions coordinated by 3 sulfur atoms (CN = 3.0). The As–S interatomic distance of the first shell is calculated at 2.279 A and the Debye–Waller factor (σ 2 ) is 0.00427. These data suggest that the modeled structure of the studied precipitates is slightly S-deficient and ordered only in the first shell around As, resembling an Orpiment-type structure, whereas higher shells are not present and must be disordered. The disorder phenomenon may be strictly produced either by the existence of occasional As–S–As bridges with As–As bonds or by the occurrence of As–O–As bridges, causing twisting of the AsS 3 pyramids in the initial Orpiment structure. This distortion in the higher coordination shells of the structural sheets creates the amorphous Orpiment.
Joris Dik - One of the best experts on this subject based on the ideXlab platform.
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Artificial Orpiment, a new pigment in Rembrandt’s palette
Heritage Science, 2017Co-Authors: Annelies Van Loon, Petria Noble, Anna Krekeler, Yoshinari Abe, Izumi Nakai, Koen Janssens, Geert Van Der Snickt, Joris DikAbstract:This paper reports on how the application of macro X-ray fluorescence (MA-XRF) imaging, in combination with the re-examination of existing paint cross-sections, has led to the discovery of a new pigment in Rembrandt’s palette: artificial Orpiment. In the NWO Science4Arts ‘ReVisRembrandt’ project, novel chemical imaging techniques are being developed and applied to the study of Rembrandt’s late paintings in order to help resolve outstanding questions and to gain a better understanding of his late enigmatic painting technique. One of the selected case studies is the Portrait of a Couple as Isaac and Rebecca, known as ‘The Jewish Bride’, dated c. 1665 and on view in the Rijksmuseum. During the re-installation of the Rijksmuseum in 2013, the picture was scanned using the Bruker M6 Jetstream MA-XRF scanner. The resulting elemental distribution maps made it possible to distinguish many features in the painting, such as bone black remains of the original hat (P, Ca maps), and the now discolored smalt-rich background (Co, Ni, As, K maps). The arsenic (As) map also revealed areas of high-intensity in Isaac’s sleeve and Rebecca’s dress where it could be established that it was not related with the pigment smalt that also contains arsenic. This pointed to the presence of a yellow or orange arsenic-containing pigment, such as realgar or Orpiment that is not associated with the artist’s palette. Subsequent examination of existing paint cross-sections from these locations taken by Karin Groen in the 1990s identified isolated, almost perfectly round particles of arsenic sulfide. The round shape corresponds with published findings on a purified form of artificial Orpiment glass obtained by dry processing, a sublimation reaction. In bright field, the particles characteristically exhibit a dark cross in the middle caused by internal light reflections. The results of additional non-invasive techniques (portable XRD and portable Raman) are discussed, as well as the implications of this finding and how it fits with Rembrandt’s late experimental painting technique.
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Artificial Orpiment, a new pigment in Rembrandt's palette
Heritage Science, 2017Co-Authors: Annelies Van Loon, Petria Noble, Anna Krekeler, Yoshinari Abe, Izumi Nakai, Geert Van Der Snickt, Koen Janssens, Joris DikAbstract:This paper reports on how the application of macro X-ray fluorescence (MA-XRF) imaging, in combination with the re-examination of existing paint cross-sections, has led to the discovery of a new pigment in Rembrandt’s palette: artificial Orpiment. In the NWO Science4Arts ‘ReVisRembrandt’ project, novel chemical imaging techniques are being developed and applied to the study of Rembrandt’s late paintings in order to help resolve outstanding questions and to gain a better understanding of his late enigmatic painting technique. One of the selected case studies is the Portrait of a Couple as Isaac and Rebecca, known as ‘The Jewish Bride’, dated c. 1665 and on view in the Rijksmuseum. During the re-installation of the Rijksmuseum in 2013, the picture was scanned using the Bruker M6 Jetstream MA-XRF scanner. The resulting elemental distribution maps made it possible to distinguish many features in the painting, such as bone black remains of the original hat (P, Ca maps), and the now discolored smalt-rich background (Co, Ni, As, K maps). The arsenic (As) map also revealed areas of high-intensity in Isaac’s sleeve and Rebecca’s dress where it could be established that it was not related with the pigment smalt that also contains arsenic. This pointed to the presence of a yellow or orange arsenic-containing pigment, such as realgar or Orpiment that is not associated with the artist’s palette. Subsequent examination of existing paint cross-sections from these locations taken by Karin Groen in the 1990s identified isolated, almost perfectly round particles of arsenic sulfide. The round shape corresponds with published findings on a purified form of artificial Orpiment glass obtained by dry processing, a sublimation reaction. In bright field, the particles characteristically exhibit a dark cross in the middle caused by internal light reflections. The results of additional non-invasive techniques (portable XRD and portable Raman) are discussed, as well as the implications of this finding and how it fits with Rembrandt’s late experimental painting technique.