{
  "version": "v4",
  "frozen": true,
  "frozen_on": "2026-10-02",
  "current": "current.json names the Trust Index issue and the price snapshot in force. Both are replaced every month; neither replacement changes these rules. A new snapshot must be built by build_reference.py from files archived in evidence/ on the snapshot date.",
  "scope": "Laboratory-grown diamonds, loose, graded by GIA or IGI. Not natural diamonds, not set jewellery.",

  "formula": "value = reference(shape, carat, colour, clarity, cut) × (1 + P5 × share)",

  "reference": {
    "source": "The Diamond Price. (2026). Diamond Price Index [Data set]. https://thediamondprice.com/data/diamond-price-index",
    "licence": "CC BY 4.0",
    "what_it_is": "Median asking prices of lab-grown diamonds listed by United States online retailers. Asking prices, not transaction prices, and not wholesale.",
    "carat": "Piecewise-linear between the published carat points. No figure below the first or above the last point.",
    "carat_range": [0.3, 5.0],
    "ladder_band": "premium",
    "ladder_band_reason": "The dataset states that its default band for lab-grown is 'high'. The ladder agrees with the 'high' medians in the CSV (1.5 ct: 1,440 against 1,511; 2 ct: 2,350 against 2,467 to 2,491) and not with the others.",
    "shape": "The source's 1 ct lab-grown shape table, each shape against round. A shape the source does not publish gets no figure.",
    "band": "Colour and clarity are read together as one quality band, as the source does; it publishes no separate colour or clarity effect. A stone's band is the lower of its colour band and its clarity band.",
    "band_grades": {
      "top":        {"colour": ["D", "E"], "clarity": ["FL", "IF", "VVS1"]},
      "premium":    {"colour": ["F"],      "clarity": ["VVS2", "VS1"]},
      "mainstream": {"colour": ["G", "H"], "clarity": ["VS2", "SI1"]}
    },
    "band_grades_note": "The source names its bands Top (D-E, VVS1-FL), Premium (E-F, VS1-VVS2), Mainstream (G-H, VS2-SI1), Entry (I-J, SI1-SI2). Where two bands share a grade (E, SI1) the stone takes the higher. Entry is not published for lab-grown, so I-K colour and SI2 or lower clarity get no figure.",
    "band_factor": "Median, across every lab-grown row of the CSV that publishes both, of that band's median over the 'high' band's median.",
    "cut": ["Excellent", "Very Good"],
    "cut_note": "The source's bands hold stones of Very Good cut or better. A lower cut gets no figure."
  },

  "dimension_weights": [30, 15, 15, 15, 10, 10, 5],
  "dimension_weights_source": "DIM_MAX in drop/track2-report/score_register.py — the index's own frozen weights, reused unchanged",
  "counts": ["corroborated_t1"],
  "counts_note": "Only an area with a claim confirmed by an independent third party counts.",
  "gate": {"requires_product_fact_t1": true},

  "premium": {
    "id": "P5",
    "pct": 9.7,
    "source": "PwC, 2024 Voice of the Consumer Survey, press release of 15 May 2024",
    "quote": "Consumers are willing to spend an average of 9.7% more on sustainably produced or sourced goods",
    "basis": "Stated willingness to pay across all consumer goods, more than 20,000 consumers in 31 countries and territories. Not specific to diamonds and not a measured transaction premium; the release itself says it may not translate into actual spend.",
    "archived": "evidence/pwc-voc-2024-excerpt.txt"
  },

  "integrity": {"contradicted_product_fact_zero": true, "governance_flag_zero": true},
  "under_review": "A house under review is valued at the stone's market reference with nothing added. No premium is printed while a review is open.",
  "no_figure_when": ["not_in_index", "stone_outside_published_reference"],
  "rounding": "to the nearest 10 USD"
}