han blue han blue han blue han blue han blue han blue han blue

han blue

BaCuSi₄O₁₀

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background

Han Blue is one of the earliest known synthetic pigments, developed in China approximately 2,500 years ago during the Warring States period. It was prominently used to decorate the famous Terracotta Warriors of Xi'an and appears in numerous artifacts from the Han Dynasty, from which it derives its name. The pigment represents a remarkable achievement in ancient chemistry, requiring precise control of temperature and atmosphere during synthesis.

preparation

Mixes cleanly with earth tones and other mineral pigments. Creates sophisticated grays when combined with raw umber. Pairs beautifully with Han Purple for historically accurate palettes. Avoid mixing with sulfide-based pigments.

safety

see research material safety brief

GHS Classificationref
Not classified as hazardous under CLP/GHS per analog SDSKremer Pigmente MSDS 10071; treat conservatively as particulate
Hazardsref
Inhalation (primary): respirable dust; mechanical eye/skin irritation; avoid ingestioninsoluble ceramic pigment; acids may increase Ba/Cu bioavailability
Recommended PPEref
N95 minimum; P100 for milling/transfers; nitrile gloves; safety glasses; lab coatuse LEV or fume hood; HEPA vacuum for cleanup; no compressed air
Exposure Notesref
Wet methods preferred; avoid dry sweeping; wash hands after handling; no eating/drinking in work areahigh-dust ops: milling, sieving, compressed air cleanup
Storageref
Sealed container, cool/dry; segregate from strong acids/bases; secondary containment recommendedstore away from food prep and living areas
Disposalref
Dispose as inorganic pigment waste per local regulations; do not drain; bag contaminated wipes/filtersif acid-exposed, treat as heavy-metal-containing waste

ec data (coming soon)

The following measurements are pending elemental color laboratory analysis:

  • GHS Classification
  • Hazards
  • Recommended PPE
  • Exposure Notes
  • Storage
  • Disposal
  • Category
  • Opacity Class
  • ASTM / ISO References
  • Lightfastness (Std.)
  • Oil Absorption (Std.)
  • Chemical Formula
  • Crystal Structure
  • Particle Size
  • Refractive Index
  • Specific Gravity
  • Phase / Identity
  • Family
  • Synthesis Class
  • Hue Bias
  • Opacity
  • Scattering Regime
  • NIR Response
  • Fluorescence
  • Oil Absorption
  • Binder Compatibility
  • Chemical Stability

identifiers

Categoryref
Bluestore taxonomy bucket
Opacity Classref
Opaque to semi-opaque (particle-size dependent)qualitative classification

standards

ASTM / ISO Referencesref
ASTM/ISO references listed here are method references only unless EC measurements are presentkeeps the page honest
Lightfastness (Std.)ref
ASTM D4303 (method family reference)reference standard only — not yet tested on EC material to date
Oil Absorption (Std.)ref
Commonly reported via standardized oil absorption methods (method reference)reference only — not yet tested on EC material to date

chemical

Chemical Formularef
BaCuSi₄O₁₀literature / phase designation
Crystal Structureref
Tetragonalreported crystal system for BaCuSi₂O₆
Particle Sizeref
5–15 µmtypical pigment grind (literature / supplier range)
Refractive Indexref
1.636literature value (conditions often reported near 589 nm)
Specific Gravityref
3.8typical / literature density
Phase / Identityref
BaCuSi₂O₆ (Han Blue)target phase / identity
Familyref
Barium copper silicatematerials family
Synthesis Classref
Solid-state (historically high-temperature synthesis)process class (not a batch claim)

optical

Hue Biasref
Cool blue with slight violet bias under daylightqualitative descriptor
Opacityref
High (mineral pigment; particle-size dependent)qualitative; depends on grind and binder
Scattering Regimeref
Mie-dominant (particle-size dependent)qualitative; depends on PSD and binder RI
NIR Responseref
NIR luminescence (~900 nm) under red excitation (~650 nm)well-known diagnostic property used in heritage science
Fluorescenceref
Occasional weak UV-A fluorescence reported in some preparationsbatch/process dependent; treat as qualitative

physical

Oil Absorptionref
25–30 g oil / 100 g pigmenttypical range; depends on grind and surface area
Binder Compatibilityref
Compatible with common binders (oil, acrylic, gum arabic, egg tempera, casein); lime-safegeneral compatibility claim; verify per binder system if critical
Chemical Stabilityref
High thermal and photochemical stability under normal artist use; decomposes at extreme high temperaturesummary statement; see testing notes

references

core info

literature

  • doi 10.1007/s00216-009-2693-0
    spatially resolved characterisation of Egyptian blue, Han blue and Han purple by photo-induced luminescence digital imaging · 2009 · The photo-induced luminescence properties of Egyptian blue, Han blue and Han purple were investigated by means of near-infrared digital imaging. These pigments emit infrared radiation when excited in the visible range. The emission can be recorded by means of a modified commercial digital camera equipped with suitable glass filters. A variety of visible light sources were investigated to test their ability to excite luminescence in the pigments. Light-emitting diodes, which do not emit stray infrared radiation, proved an excellent source for the excitation of luminescence in all three compounds.
  • doi 10.1016/j.forsciint.2024.112172
    Preliminary investigations into the use of the ancient pigments Han blue and Han purple as luminescent dusting powders for the detection of latent fingermarks · 2024 · 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.
  • doi 10.3791/51686
    Exfoliation of Egyptian Blue and Han Blue, Two Alkali Earth Copper Silicate-based Pigments · 2014 · In a visualized example of the ancient past connecting with modern times, we describe the preparation and exfoliation of CaCuSi4O10 and BaCuSi4O10, the colored components of the historic Egyptian blue and Han blue pigments. The bulk forms of these materials are synthesized by both melt flux and solid-state routes, which provide some control over the crystallite size of the product. The melt flux process is time intensive, but it produces relatively large crystals at lower reaction temperatures. In comparison, the solid-state method is quicker yet requires higher reaction temperatures and yields smaller crystallites. Upon stirring in hot water, CaCuSi4O10 spontaneously exfoliates into monolayer nanosheets, which are characterized by TEM and PXRD. BaCuSi4O10 on the other hand requires ultrasonication in organic solvents to achieve exfoliation. Near infrared imaging illustrates that both the bulk and nanosheet forms of CaCuSi4O10 and BaCuSi4O10 are strong near infrared emitters. Aqueous CaCuSi4O10 and BaCuSi4O10 nanosheet dispersions are useful because they provide a new way to handle, characterize, and process these materials in colloidal form.
  • doi 0.1111/arcm.70083
    A Northern Connection: Spread of Faience, Glass and Han Blue Into the Chengdu Plain During the Warring States Period · 2025 · Eighteen fragments of glass and vitreous materials from the Warring States period Feihu cemetery, Chengdu Plain, were analysed by LA-ICP-MS, SEM-EDS and XRD. The assemblage comprises potassium-silica-lime faience and glass, low-calcium soda-lead-barium faience and glass, and Han blue.
  • doi 0.1016/j.jpcs.2015.04.021
    Heat capacity, thermal expansion and heat transport in the Han Blue (BaCuSi4O10): Observation of structural phase transitions · 2015 · Structural phase transitions at 87K and 103K are reported for single-crystalline Han Blue (BaCuSi4O10) by means of high-resolution thermal-expansion, thermal conductivity and heat capacity measurements. The phase transition at 103K results in differing lengths of the a and b lattice parameters, and thus a lowering of the crystallographic symmetry. Negative thermal-expansion coefficients are observed perpendicular to the c-axis over a wide temperature range (108K
  • doi 0.1021/acs.jchemed.5b00288
    Origin of the Anomalous Color of Egyptian and Han Blue Historical Pigments: Going beyond the Complex Approximation in Ligand Field Theory · 2016 · 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, E R(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 E R(r) field produces huge shifts, up to ∼0.9 eV, in their d–d transitions, which are unusual compared to the majority of compounds containing the same square-planar CuO4 6– chromophore. The relevance of the internal field for explaining phenomena such as the distinct color of ruby and emerald or the optical spectrum of CuF6 4– complexes in layered perovskites is also emphasized.

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