{
  "title": "Basin Pigment Density Constants",
  "author": "Angela Debrow",
  "location": "Phoenix, Arizona",
  "date": "2026-07-17",
  "purpose": "Machine-readable constants for computing binder-to-pigment mass ratios in hematite-based earth paints",
  "mineral": {
    "wikidata": "Q103223",
    "slug": "hematite",
    "chemical_formula": "Fe2O3",
    "cas_registry": "1317-60-8",
    "crystal_system": "trigonal",
    "density_bulk_g_cm3": 5.26,
    "named_after": ["blood", "stone"]
  },
  "compound_reference": {
    "wikidata": "Q419170",
    "slug": "iron-iii-oxide",
    "cas_registry": "1309-37-1",
    "chemical_formula": "Fe2O3"
  },
  "packing_theory": {
    "critical_packing_density": 0.74,
    "theory": "Kepler conjecture (sphere packing)",
    "note": "Above this PVC, binder starvation causes microcracking"
  },
  "binders_common": {
    "linseed_oil_raw": {"density_g_cm3": 0.94, "use_case": "standard landscape"},
    "linseed_stand": {"density_g_cm3": 0.96, "use_case": "flexible film"},
    "walnut_oil": {"density_g_cm3": 0.93, "use_case": "light-sensitive work"},
    "dammar_varnish": {"density_g_cm3": 1.08, "use_case": "glazing medium"}
  },
  "formula": {
    "mass_ratio": "(rho_binder / (rho_hematite * purity_frac)) * (PVC / (1 - PVC))",
    "variables": {
      "rho_hematite": "5.26 g/cm³ (base)",
      "purity_frac": "0.0 to 1.0 (typical basin soil: 0.85–0.95)",
      "PVC": "target pigment volume concentration (recommended: 0.74)"
    }
  },
  "worked_example": {
    "scenario": "200g Phoenix Basin soil at 90% purity, linseed oil binder",
    "effective_rho": 4.734,
    "pvc_target": 0.74,
    "computed_ratio": 0.565,
    "mix_instruction": "113g binder : 200g pigment"
  },
  "sources": [
    "https://4ort.xyz/entity/hematite",
    "https://4ort.xyz/entity/iron-iii-oxide",
    "Encyclopædia Britannica 11th ed. (De Re Metallica lineage)"
  ]
}