BaCuSi2O6 Research Articles

Preliminary investigations into the use of the ancient pigments Han blue and Han purple as luminescent dusting powders for the detection of latent fingermarks

Here we present our preliminary studies into the inorganic pigments Han blue (BaCuSi4O10) and Han purple (BaCuSi2O6) as near-infrared luminescent fingerprint dusting powders. These pigments were developed in ancient China around 800 BCE and both show luminescence in the NIR region. There remains, however, ambiguity in the literature concerning their photophysical properties. Samples of Han blue and Han purple artist’s pigments were characterized by optical microscopy, infrared, ultraviolet-visible absorbance and luminescence spectroscopy. Their performance as fingerprint dusting powders, without any further treatment, on non-porous surfaces were compared to exfoliated lipophilic coated Egyptian blue and commercial fluorescent powders in a pilot study. These results demonstrate for the first time that both ancient pigments show promise as alternative dusting powders for latent fingermarks.

Study of barium copper silicate pigments on painted pottery from the Qinhan Xincheng, Western Han Dynasty (207 B.C.–8 A.D.), Xi’an, Shaanxi province, China

Lead-barium silicate system products, represented by barium copper silicate and lead-barium glass, epitomize a unique artistic craftsmanship of ancient China. Specifically, barium copper silicate products were the only known artificially synthesized blue-purple inorganic pigments in ancient China. Painted pottery decorated with barium copper silicate pigment, predominantly found in elite tombs after 2nd century B.C., is exceedingly rare and holds immense archaeological significance. This case employed multi micro-scale analytical techniques, such as ultra-depth-of-field microscopy, Raman spectroscopy, µ X-ray Diffraction, and electron probe microanalysis, for comprehensive microscopic examination of a rare Chinese Purple (CP, BaCuSi2O6) pigments on painted pottery. The analytical results confirm that the purple pigment is BaCuSi2O6, accompanied by cinnabar for the red and bone white for the white sections, suggesting the probable use of organic residues as an adhesive. Additionally, the study reveals microstructural characteristics in CP faience and CP pigments, notably the encapsulation of CP particles by quartz particles. Therefore, it can be hypothesized that the process of manufacturing purple pigment was achieved by grinding faience into fine particles and then using an organic-based adhesive to adhere these particles to the pottery. This implies that the evolutions in CP products circa the 2nd century B.C. were driven not by technological advances from lead-barium glass, but rather by shifts in application methods, reflecting an adaptation process among different cultures. This study provides new perspectives and significant insights for comprehending the interplay between barium copper silicate and lead-barium glass, reconstructing ancient pottery painting techniques, and exploring the era’s technological and cultural interactions.

НАУЧНЫЙ АНАЛИЗ ФИОЛЕТОВОГО ВОСЬМИУГОЛЬНОГО СТОЛБЧАТОГО ИЗДЕЛИЯ, НАЙДЕННОГО НА МОГИЛЬНИКЕ ХЭЦЗЯ, СЯНЬЯН, ШЭНЬСИ, И СВЯЗАННЫЕ С ЭТИМ ВОПРОСЫ

In this paper, we chose late war purple octagonal prismatic ware excavated at the Hejia Cemetery in Xianyang as the object of study, and carried out scientific analysis using ultra-deep field microscopy, scanning electron microscopy and energy spectrum analysis, X-ray diffraction, and microscopic Raman spectroscopy. First of all, the features of the formation and weathering process were determined, then the samples of unweathered areas obtained by the sectioning method were examined, and it was confirmed that all 12 samples are barium copper silicate with the main phases of Chinese violet (BaCuSi2O6) and Chinese dark blue (BaCu2Si2O7) colors. Based on compositional characteristics, etc. it was also found that this group of purple octagonal vessels embodies two different manufacturing processes and may represent an evolution of the process from lead-barium glass to cupro-barium silicate. On this basis, issues such as the population, distribution area and functional characteristics of this type of dish are discussed in order to obtain new ideas and evidence for relevant research.

Investigating field-induced magnetic order in Han purple by neutron scattering up to 25.9 T

BaCuSi$_2$O$_6$ is a quasi-two-dimensional (2D) quantum antiferromagnet containing three different types of stacked, square-lattice bilayer hosting spin-1/2 dimers. Although this compound has been studied extensively over the last two decades, the critical applied magnetic field required to close the dimer spin gap and induce magnetic order, which exceeds 23 T, has to date precluded any kind of neutron scattering investigation. However, the HFM/EXED instrument at the Helmholtz-Zentrum Berlin made this possible at magnetic fields up to 25.9 T. Thus we have used HFM/EXED to investigate the field-induced ordered phase, in particular to look for quasi-2D physics arising from the layered structure and from the different bilayer types. From neutron diffraction data, we determined the global dependence of the magnetic order parameter on both magnetic field and temperature, finding a form consistent with 3D quantum critical scaling; from this we deduce that the quasi-2D interactions and nonuniform layering of BaCuSi$_2$O$_6$ are not anisotropic enough to induce hallmarks of 2D physics. From neutron spectroscopy data, we measured the dispersion of the strongly Zeeman-split magnetic excitations, finding good agreement with the zero-field interaction parameters of BaCuSi$_2$O$_6$. We conclude that HFM/EXED allowed a significant extension in the application of neutron scattering techniques to the field range above 20 T and in particular opened new horizons in the study of field-induced magnetic quantum phase transitions.

Preparation, properties and applications of near-infrared fluorescent silicate nanosheets.

The layered silicates Egyptian Blue (CaCuSi4O10, EB), Han Blue (BaCuSi4O10, HB) and Han Purple (BaCuSi2O6, HP) are known as historic pigments, but they also possess novel optoelectronic properties with great potential for fundamental research and technology. They fluoresce in the near-infrared (NIR) range and can be exfoliated into two-dimensional (2D) nanomaterials (i.e. nanosheets, NS) which retain the photophysical properties of the bulk materials. These and other characteristics fuel the growing excitement of the scientific community about these materials. EB-, HB- and HP-NS have been used in various applications ranging from smart inks, energy storage, bioimaging, to phototherapy and more. In this review article, we report the fundamental properties of these low-dimensional silicate nanomaterials, discuss applications and outline perspectives for the future.

Revealing three-dimensional quantum criticality by Sr substitution in Han purple

Classical and quantum phase transitions (QPTs), with their accompanying concepts of criticality and universality, are a cornerstone of statistical thermodynamics. An exemplary controlled QPT is the field-induced magnetic ordering of a gapped quantum magnet. Although numerous "quasi-one-dimensional" coupled spin-chain and -ladder materials are known whose ordering transition is three-dimensional (3D), quasi-2D systems are special for several physical reasons. Motivated by the ancient pigment Han Purple (BaCuSi$_{2}$O$_{6}$), a quasi-2D material displaying anomalous critical properties, we present a complete analysis of Ba$_{0.9}$Sr$_{0.1}$CuSi$_{2}$O$_{6}$. We measure the zero-field magnetic excitations by neutron spectroscopy and deduce the magnetic Hamiltonian. We probe the field-induced transition by combining magnetization, specific-heat, torque and magnetocalorimetric measurements with low-temperature nuclear magnetic resonance studies near the QPT. By a Bayesian statistical analysis and large-scale Quantum Monte Carlo simulations, we demonstrate unambiguously that observable 3D quantum critical scaling is restored by the structural simplification arising from light Sr-substitution in Han Purple.

Exfoliated Silicate Nanosheets As Novel Near-Infrared Fluorophores for (Bio)Photonics

The near-infrared (NIR) region of the electromagnetic spectrum presents optimal characteristics for imaging of complex (biological) samples: this is mainly due to reduced light scattering, absorption, phototoxicity and autofluorescence. However, despite their clear potential over commonly employed visible fluorophores, only few NIR fluorescent materials are known so far, and even less are suitable for biomedical applications. For this reason, it is of great interest to search for novel materials that can enrich the so far poor library of NIR fluorophores.We exfoliated a class of layered silicates: Egyptian Blue (CaCuSi4O10, EB), Han Blue (BaCuSi4O10, HB) and Han Purple (BaCuSi2O6, HP). These pigments fluoresce in the NIR (λ emi ≈ 920-950 nm) with a long excited state lifetime (τ ≈ 10-100 µs). By milling, tip sonication and several centrifugation steps, small and monodisperse 2D nanosheets (NS) could be exfoliated. Most interestingly, the intense NIR fluorescence emission of the bulk counterparts is retained. In comparison to state-of-the-art fluorophores, EB-NS show no bleaching while displaying outstanding fluorescence intensity. Such qualities of EB-NS enabled us to inject them into systems of biological relevance such as developing Drosophila embryos, and perform in vivo single-particle tracking and microrheology measurements. Furthermore, it is possible to successfully detect EB-NS in plants. [1] In general, all the above mentioned three silicate NS prove bright enough to be imaged through several cm of tissue phantoms, which demonstrates the potential for (bio)photonics. Finally, we used the microsecond fluorescence lifetimes of EB-NS, HB-NS and HP-NS for micro- and macroscopic fluorescence lifetime imaging (FLIM). The results show that lifetime engineering of these silicate nanostructures is possible and can be used for lifetime-encoded imaging. [2]In summary, we present a new exfoliation route that yields NIR fluorescent nanosheets of high promise as novel NIR fluorophores for bioimaging and photonics.Literature:[1] G. Selvaggio et al., Nat. Commun. 2020, 11, 1495.[2] G. Selvaggio et al., in preparation.

Photophysical properties and fluorescence lifetime imaging of exfoliated near-infrared fluorescent silicate nanosheets.

The layered silicates Egyptian Blue (CaCuSi4O10, EB), Han Blue (BaCuSi4O10, HB) and Han Purple (BaCuSi2O6, HP) emit as bulk materials bright and stable fluorescence in the near-infrared (NIR), which is of high interest for (bio)photonics due to minimal scattering, absorption and phototoxicity in this spectral range. So far the optical properties of nanosheets (NS) of these silicates are poorly understood. Here, we exfoliate them into monodisperse nanosheets, report their physicochemical properties and use them for (bio)photonics. The approach uses ball milling followed by tip sonication and centrifugation steps to exfoliate the silicates into NS with lateral size and thickness down to ≈ 16–27 nm and 1–4 nm, respectively. They emit at ≈ 927 nm (EB-NS), 953 nm (HB-NS) and 924 nm (HP-NS), and single NS can be imaged in the NIR. The fluorescence lifetimes decrease from ≈ 30–100 μs (bulk) to 17 μs (EB-NS), 8 μs (HB-NS) and 7 μs (HP-NS), thus enabling lifetime-encoded multicolor imaging both on the microscopic and the macroscopic scale. Finally, remote imaging through tissue phantoms reveals the potential for bioimaging. In summary, we report a procedure to gain monodisperse NIR fluorescent silicate nanosheets, determine their size-dependent photophysical properties and showcase the potential for NIR photonics.

Scientific analysis of some glazed pottery unearthed from Warring States Chu tombs in Jiangling, Hubei Province: Indication for the origin of the low‐fired glazed pottery in China

A portable energy dispersive X‐ray fluorescence spectrometer and a micro‐Raman spectrometer are used for the nondestructive analysis of a batch of glazed pottery ornaments unearthed from Warring States Chu (楚) tombs (B.C.475–B.C.221) in Jiangling, Hubei Province, China. According to the chemical compositions obtained, all of the glazes belong to the lead–barium–silicate (PbO–BaO–SiO2) system and contain certain levels of copper. The man‐made barium copper silicate pigment crystals, such as Chinese blue (BaCuSi4O10) and Chinese purple (BaCuSi2O6), are identified from several samples by micro‐Raman spectrometer. Besides, gypsum and hematite are found in the white and brown regions of two eye beads. Combined with other glazed pottery and the related silicate artifacts (e.g., lead–barium glass and faience, potash–lime glass and glazed pottery, high‐lead glazed pottery, etc.), the origin, development, and affected factors of ancient Chinese low‐fired glazed pottery have been discussed preliminarily. The present study provides principal evidences for the technological provenance, raw material recipes, and the relationship between low‐fired glazed pottery and related vitreous materials of ancient China. It also provides some significant clues for the origin and the development of ancient Chinese lead–barium glass.

Man-made blue and purple barium copper silicate pigments and the pabstite (BaSnSi3O9) mystery of ancient Chinese wall paintings from Luoyang

Man-made ancient Chinese barium copper silicate pigments: Chinese (Han) Purple, BaCuSi2O6; Chinese (Han) Blue, BaCuSi4O10; Chinese Dark Blue, BaCu2Si2O7 (in summary called Chinese blues), and platelet-like crystals of BaSnSi3O9 were detected on mural paintings of a tomb in Luoyang City, Henan Province, China, dated to Western Han Dynasty (206 BC–8 AD). The pigments of the LY01 and LY02 samples were analyzed by archaeometrical methods: powder X-ray diffractometry (XRD), scanning electron microscopy (SEM–EDX) and micro-Raman spectroscopy. While the artificial nature of the ancient barium copper silicates was undoubted, the synthetic or mineral origin of BaSnSi3O9 of these murals had to be clarified. Involvement of the rare mineral pabstite Ba(Sn,Ti,Zr)Si3O9 from the Tian Shan mountains could be ruled out due to absence of Ti and Zr in the elemental composition. Tin compounds as admixtures to the lead minerals—the latter required as flux additive for the preparation of the Chinese blues—or tin admixtures to pristine barium starting minerals could be excluded, as well as the use of tin containing mineral mushistonite (CuSn(OH)6), primarily intended to be applied as copper source. Related to the findings for the production of Egyptian Blue (CaCuSi4O10), bronze or bronze scrap including also corroded material was used intending copper recycling. For the synthesis of the Luoyang Chinese blues only low amounts of bronze or bronze scrap were required providing the additional advantage to form in presence of air a tin/lead oxide flux with lowered vitrification temperatures and viscosities. This marked the advent of an ‘innovative production technology’ avoiding addition of large amounts of lead minerals as an effective lead-only flux. Despite of the chemical similarity to production of Egyptian Blue, the tin/lead based developments for the Chinese blues were anticipated to be independent excluding technology transfer from ancient Egypt. For further substantiation of the appearance of pabstite in the Luoyang Chinese blues a contemporary independent synthesis was sought, carried out under conditions similar to those of the barium copper silicate syntheses (1000 °C, but absence of a flux) starting from cassiterite (SnO2), quartz (SiO2) and witherite (BaCO3).

Identification of PbO (BaO) faience from an early and middle Warring States period cemetery at Zhaitouhe, northern Shaanxi, China

Low‐temperature vitreous materials fluxed with lead (and barium) appeared in the early Warring States period (c.fifth century bce) in ancient China. A range of lead vitreous products fluxed with the same agent, including faience/glass beads, glazed pottery and Chinese blue (purple) pigment, were developed subsequently. This study carries out scientific analysis of six vitreous beads unearthed from the Zhaitouhe cemetery site in northern Shaanxi dating to the early and middle Warring States period to investigate their chemical composition, microstructure and coloration. The lead (and barium) vitreous beads identified here are some of the earliest lead vitreous materials discovered in China so far, and therefore important for the study of the development of lead vitreous technologies in ancient China. This paper also points out that it is meaningful to evaluate the lead glass, glazed pottery and barium copper silicate pigments as a whole technological assemblage given their close relationships.

An Exfoliated 2D Egyptian Blue Nanosheet for Highly Selective Enrichment of Multi-phosphorylated Peptides in Mass Spectrometric Analysis.

Phosphopeptide enrichment is essential for the phosphoprotein profiling, due to the low abundance in complex biological samples. Moreover, selective binding of multi-phosphopeptides over mono-phosphopeptides is rarely established, but strongly needed in real sample analysis, especially for the investigation of cell behaviors with the multisite phosphorylation cascades. Here two-dimensional (2D) nanosheets were synthesized of Egyptian blue (CaCuSi4 O10 ), the well-known ancient pigment, and its analogues (SrCuSi4 O10 and BaCuSi4 O10 ), which were employed in the enrichment of phosphopeptides for the first time. Surprisingly, the 2D CaCuSi4 O10 nanosheet was highly selective towards multi-phosphopeptides without enriching the mono-phosphorylated peptides in a wide range of acidic conditions or buffer compositions. Meanwhile, the SrCuSi4 O10 and BaCuSi4 O10 nanosheet analogues do not exhibit this unique selectivity. Moreover, the ultrathin and well-defined 2D morphology, with abundant CaII , of Egyptian blue nanosheet was applied in cortical samples of forebrain specific PDK1 conditional knockout mice and their age-matched littermate controls, that are associated with Alzheimer's disease. The as-prepared 2D CaCuSi4 O10 nanosheet not only showed specific selectivity, but also exhibited high sensitivity (detection limit of 4×10-7 m).

Quasi-two-dimensional Bose-Einstein condensation of spin triplets in the dimerized quantum magnetBa2CuSi2O6Cl2

We synthesized single crystals of composition Ba$_2$CuSi$_2$O$_6$Cl$_2$ and investigated its quantum magnetic properties. The crystal structure is closely related to that of the quasi-two-dimensional (2D) dimerized magnet BaCuSi$_2$O$_6$ also known as Han purple. Ba$_2$CuSi$_2$O$_6$Cl$_2$ has a singlet ground state with an excitation gap of ${\Delta}/k_{\rm B}\,{=}\,20.8$ K. The magnetization curves for two different field directions almost perfectly coincide when normalized by the $g$-factor except for a small jump anomaly for a magnetic field perpendicular to the $c$ axis. The magnetization curve with a nonlinear slope above the critical field is in excellent agreement with exact-diagonalization calculations based on a 2D coupled spin-dimer model. Individual exchange constants are also evaluated using density functional theory (DFT). The DFT results demonstrate a 2D exchange network and weak frustration between interdimer exchange interactions, supported by weak spin-lattice coupling implied from our magnetostriction data. The magnetic-field-induced spin ordering in Ba$_2$CuSi$_2$O$_6$Cl$_2$ is described as the quasi-2D Bose-Einstein condensation of triplets.

Dual wavelength excitation for the time-resolved photoluminescence imaging of painted ancient Egyptian objects

The scientific imaging of works of art is crucial for the assessment of the presence and distribution of pigments and other materials on surfaces. It is known that some ancient pigments are luminescent: these include pink red-lakes and the blue and purple pigments Egyptian Blue (CaCuSi4O10), Han blue (BaCuSi4O10) and Han purple (BaCuSi2O6). Indeed, the unique near-infrared luminescence emission of Egyptian blue allows the imaging of its distribution on surfaces. We focus on the imaging of the time-resolved photoluminescence of ancient Egyptian objects in the Burri Collection from the Civic Museum of Crema and of the Cremasco (Italy). Time-resolved photoluminescence images have been acquired using excitation at 355 nm for detecting the ns-emission of red lakes and binding media; by employing 532 nm excitation Egyptian blue is probed, and the spatial distribution of its long-lived microsecond emission is imaged. For the first time we provide data on the photoluminescence lifetime of Egyptian blue directly from objects. Moreover, we demonstrate that the use of a pulsed laser emitting at two different wavelengths increases the effectiveness of the lifetime imaging technique for mapping the presence of emissions from pigments on painted surfaces. Laser-induced luminescence spectra from different areas of the objects and traditional digital imaging, using led-based lamps, long pass filters and a commercial photographic camera, complement the results from photoluminescence lifetime imaging. We demonstrate the versatility of a new instrumental setup, capable of recording decay emission kinetics with lifetimes from nanosecond to microseconds. While the combined wavelength approach for the imaging of emissions from different materials has been demonstrated for the study of ancient Egyptian pigments (both organic and inorganic), the method could be extended to the analysis of modern pigments and paintings.

Colinowensite, BaCuSi2O6, a new mineral from the Kalahari Manganese Field, South Africa and new data on wesselsite, SrCuSi4O10

AbstractA new silicate, colinowensite, BaCuSi2O6, has been found in the Wessels mine, Kalahari Manganese Field, South Africa. It is associated with effenbergerite, wesselsite, lavinskyite, scottyite, diegogattaite, as well as with pectolite, quartz, aegirine, richterite, minerals of the garnet group and a number of different manganese and iron oxides, especially hausmannite and hematite. The mineral was named for the mineral collector and finder of the new species, Colin R. Owens, of Somerset West, South Africa. Colinowensite is brittle, with uneven fracture, and the estimated Mohs hardness is ∼4. It occurs as subhedral crystals <100 μm in size. The forms {100} and {110} are observed while {001} is always present in cleavage plates. The calculated density is 4.236 g cm–3. It is the natural analogue of the synthetic pigmentreferred to as Chinese or Han purple, which is found on artifacts from ancient and imperial China. The mineral is of dark blue to purple colour, with a purple streak, and is uniaxial (–), with ω = 1.740 (20), ε = 1.735 (20) (420 nm) and ω = 1.745 (20), ε = 1.730(20) (650 nm). The lustre is vitreous and no fluorescence is observed under either shortwave or longwave ultraviolet radiation. Avery strong pleochroism occurs from purple along the c axis to blue in a perpendicular direction. Colinowensite is not soluble in acids except HF. Electron microprobe analyses gave an average composition (wt.%) of CuO 22.53, BaO 43.43 and SiO2 34.04 yielding the empirical formula (based on 6 O a.p.f.u.) BaCuSi2O6. The new mineral is tetragonal, space group I41/acd with Z = 16, anda = 9.967(1), c = 22.290 (2) Å. Colinowensite is a cyclosilicate with [Si4O12]8– 4-membered single rings, arranged in sheets parallel to (001). The structure is further characterized by CuO4 squares sharing corners with four neighbouring silicate rings within a sheet. Ba2+ cations are bonded to ten O atoms in irregular coordination. Average Si–O, Cu–O and Ba–O bond lengths are 1.619, 1.934 and 2.943 Å, respectively. Colinowensite belongs to subdivision 9. CE of the Strunz Mineralogical Tables. In addition, based on single-crystal X-ray work, new structural data for wesselsite of chemical composition Sr0.9Ba0.1CuSi4O10 are provided.

Visible-induced luminescence imaging: A user-friendly method based on a system of interchangeable and tunable LED light sources

Imaging techniques represent an unavoidable analytical tool for the non-invasive investigation of cultural heritage objects providing useful information for the identification and distribution of materials on the investigated surface. In particular, photo-induced luminescence imaging can give important indications as to the distribution of organic (binders, resins, dyes and lakes) and inorganic (Egyptian blue, Han blue, Han purple, zinc oxide, cadmium based pigments) constituting materials. Recently the use of LEDs, generating a narrow emission band in the Visible range, has been introduced opening up a new perspective in the detection of inorganic luminescent pigments. In this work we propose a user-friendly tool for luminescence acquisition based on the use of a custom made interchangeable and tunable LED light source system, that allows us to select both the power and the wavelength of the excitation light. The study involved the analysis of panel painting replicas prepared applying several pigments and lakes commonly used by artists in different historical periods. The luminescence images were recorded by a high sensitivity CCD camera and a Vidicon camera in the Visible and NIR range, under three excitation narrow bands (red LEDs at 630nm; green LEDs at 517nm and blue LEDs at 465nm). The reliability of the developed experimental setup has been validated by spectrofluorimetric measurements. A very high correspondence between imaging and spectral response has been found concerning emission band position, emission intensity and excitation wavelength effect. Furthermore, the NIR luminescence of a modern yellow pigment, nickel titanate, has been for the first time documented. The defined methodology has been applied to the study of works of art of different historical periods where it has been proved to successfully detect luminescent inorganic and organic pigments, whose presence has been confirmed also by elemental analyses and spectrofluorimetry.

Origin of the Anomalous Color of Egyptian and Han Blue Historical Pigments: Going beyond the Complex Approximation in Ligand Field Theory

The complex approximation is widely used in the framework of the Ligand Field Theory for explaining the optical properties of crystalline coordination compounds. Here, we show that there are essential features of these systems that cannot be understood with the usual approximation that only considers an isolated complex at the correct equilibrium geometry. We also show that a quantitative understanding of such optical transitions cannot, in general, be reached unless the internal electric field, ER(r), created by the whole crystal on active electrons confined in the complex, is also taken into consideration. Seeking to prove the key role played by this internal field, usually ignored in crystalline transition metal compounds, we focus on the origin of the color displayed by the Egyptian Blue pigment (CaCuSi4O10), the first ever synthesized by humans. This pigment, together with Han Blue (BaCuSi4O10), are chosen as model systems because the anisotropic ER(r) field produces huge shifts, up to ∼0.9 eV, in th...

A Discussion on the Emergence and Development of Ancient Chinese Artificial Barium Copper Silicate Pigments from Simulation Experiments

The ancient Chinese barium copper silicate minerals mainly comprise Chinese purple (BaCuSi2O6) and Chinese blue (BaCuSi4O10), which were widely used from the late Warring States Period to the late Eastern Han Dynasty. In order to clarify the raw material of the pigment, a series of simulation experiments was conducted to produce Chinese purple pigment under varying mineral conditions. The minerals that we applied in the experiment were quartz as the source of silicon, malachite and copper oxide as the sources of copper, barite and witherite as the sources of barium and lead oxide as the source of lead. Simulation experiments showed that the barium copper silicate minerals and the purple pigment can be produced easily when witherite is used as the barium‐containing raw material. From the perspective of mineral resources, the birth of the ancient Chinese pigment associated with a unique barium mineral resource. The Chinese copper‐based pigments are assumed to have been developed independently and are presumably an outcome of historical developments in glazing techniques.

Origin of the Exotic Blue Color of Copper-Containing Historical Pigments

The study of chemical factors that influence pigment coloring is a field of fundamental interest that is still dominated by many uncertainties. In this Article, we investigate, by means of ab initio calculations, the origin of the unusual bright blue color displayed by historical Egyptian Blue (CaCuSi4O10) and Han Blue (BaCuSi4O10) pigments that is surprisingly not found in other compounds like BaCuSi2O6 or CaCuO2 containing the same CuO4(6-) chromophore. We show that the differences in hue between these systems are controlled by a large red-shift (up to 7100 cm(-1)) produced by an electrostatic field created by a lattice over the CuO4(6-) chromophore from the energy of the 3z(2)-r(2) → x(2)-y(2) transition, a nonlocal phenomenon widely ignored in the realm of transition metal chemistry and strongly dependent upon the crystal structure. Along this line, we demonstrate that, although SiO4(4-) units are not involved in the chromophore itself, the introduction of sand to create CaCuSi4O10 plays a key role in obtaining the characteristic hue of the Egyptian Blue pigment. The results presented here demonstrate the opportunity for tuning the properties of a given chromophore by modifying the structure of the insulating lattice where it is located.

Identification of the man-made barium copper silicate pigments among some ancient Chinese artifacts through spectroscopic analysis

This article describes the complementary application of non-invasive micro-Raman spectroscopy and energy dispersive X-ray fluorescence spectrometry to the characterization of some ancient Chinese silicate artifacts. A total of 28 samples dated from fourth century BC to third century AD were analyzed. The results of chemical analysis showed that the vitreous PbO–BaO–SiO2 material was used to sinter these silicate artifacts. The barium copper silicate pigments including BaCuSi4O10, BaCuSi2O6 and BaCu2Si2O7 were widely identified from colorful areas of the samples by Raman spectroscopy. In addition, other crystalline phases such as Fe2O3, BaSi2O5, BaSO4, PbCO3 and quartz were also identified. The present study provides very valuable information to trace the technical evolution of man-made barium copper silicate pigments and their close relationship with the making of ancient PbO–BaO–SiO2 glaze and glass.