Open-licensed, citation-grade reference data for jewelry — purity hallmarks, gemstones, assay offices, gemological laboratories, alloy compositions, and British date-letter cycles. JSON, CSV, SQLite. MIT licensed. JSON Schema validated.
A structured, machine-readable, source-cited reference covering six interlocking jewelry datasets. Built originally to power a phone-based jewelry identifier app; published as open data because no canonical equivalent existed.
Each record:
- Cites primary sources (ISO standards, national assay offices, FTC Jewelry Guides, gemological references)
- Validates against a published JSON Schema
- Cross-references related records by stable ID
- Includes Wikidata QIDs where available, for linked-data alignment
| Dataset | Records | Description |
|---|---|---|
hallmarks.json |
120 | Purity stamps and assay marks worldwide. Metal, purity, fineness, karat, region, aliases, alloy components, density, melting point, ISO reference, validity dates. |
gemstones.json |
49 | Gemstone reference: Mohs hardness, refractive index, specific gravity, crystal system, cleavage, common treatments, simulants, birthstone and zodiac associations. |
assay-offices.json |
15 | Current and historical assay offices: location, founding/closing dates, office mark, operator, address. |
gemological-laboratories.json |
15 | Major gem-grading laboratories (GIA, AGS, IGI, HRD, AGL, Gübelin, SSEF, GRS, CGL, GAAJ, AIGS, GIT, etc.) with scope, founding, and report types. |
karat-alloys.json |
15 | Typical alloy compositions per karat × color variant (K18YG, K18WG palladium/nickel, K18RG, K14YG, K14WG, etc.). |
british-date-letters.json |
5 | Date-letter cycle metadata for London, Birmingham, Sheffield, Edinburgh, and (closed) Chester assay offices. |
Also available:
- CSV mirrors of every dataset (auto-generated via
tools/build.py) - Minified JSON for fetch-based clients
- SQLite database combining all datasets (
dist/jewelry-reference.sqlite)
There was no canonical open dataset for jewelry hallmarks, even though the information is scattered across dozens of national assay office PDFs, gemological textbooks, and trade-press references. Software that needs to identify or describe jewelry (marketplace listing tools, valuation apps, e-commerce catalogs, museum collection systems, identification CV pipelines, LLM retrieval bases) ends up re-deriving the same tables.
This repository publishes one canonical, versioned, schema-validated, source-cited reference so downstream tools can stop reinventing it.
Single hallmark lookup with curl + jq:
curl -fsSL https://raw.githubusercontent.com/Gradient-Flow-Lab/jewelry-hallmark-reference/main/data/hallmarks.json \
| jq '.[] | select(.stamp == "K18" or (.aliases // [] | index("K18")))'Python:
import json, urllib.request
url = "https://raw.githubusercontent.com/Gradient-Flow-Lab/jewelry-hallmark-reference/main/data/hallmarks.json"
data = json.loads(urllib.request.urlopen(url).read())
k18 = next(h for h in data if h["stamp"] == "K18")
print(k18["metal"], k18["purity"], k18["alloy_components"], k18["notes"])TypeScript / Node:
const res = await fetch("https://raw.githubusercontent.com/Gradient-Flow-Lab/jewelry-hallmark-reference/main/data/hallmarks.json");
const hallmarks = await res.json();
const k18 = hallmarks.find((h: any) => h.stamp === "K18");
console.log(k18.metal, k18.purity, k18.alloy_components, k18.notes);SQL via SQLite:
sqlite3 dist/jewelry-reference.sqlite
> .tables
hallmarks gemstones assay_offices gemological_laboratories karat_alloys british_date_letters
> SELECT stamp, metal, fineness FROM hallmarks WHERE metal = 'gold' ORDER BY fineness DESC;See examples/ for runnable lookup scripts in Python, TypeScript, and bash.
Gold standards from 333 (8K, Germany) through 999.9 (four-nines bullion). Includes:
- Japanese K-prefix system (K9 through K24)
- US karat marks (10K, 14K, 18K, 22K, 24K)
- UK/Commonwealth karat marks (9ct, 18ct, 22ct, 24ct + historical 15ct)
- Continental European fineness (333, 375, 416, 417, 500, 583, 585, 625, 750, 833, 875, 916, 990, 995, 999)
- Soviet/Russian historical (583, 875)
- Hong Kong/Chinese (chuk kam 990, 1000 gold)
- Indian BIS hallmarks
- Platinum (Pt500 through Pt1000, plus international 850, 950, 1000)
- Palladium (Pd500, Pd950)
- Silver (800, 835, 900, 925, 950 French, 958 Britannia, 999) plus the STERLING, SV925, SILVER 925 word marks
- Gold-plated/filled/rolled variants (GP, GEP, HGE, GF, RGP, 1/20 14K GF, 1/30 GF, vermeil, plaqué or)
- Alternative metals (titanium, tungsten carbide, zirconium, niobium, ceramic, palladium)
- Mixed-metal techniques (mokume-gane, shakudo, shibuichi)
- Color modifiers (YG, WG, RG, PG, GG, blue gold, purple gold)
- Base metals (brass, bronze, copper, nickel silver, pinchbeck, tombac)
- British assay office symbols (lion passant, Britannia, lion's head erased, leopard's head, anchor, castle, rose, three wheatsheaves)
- National assay marks (JIS, BIS, Minerva head, eagle head, kokoshnik, Common Control Mark)
- Decorative/organic materials (jet, marcasite)
Diamond, corundum (ruby, sapphire), beryl (emerald, aquamarine, morganite, heliodor), garnet group (tsavorite, demantoid, spessartine, hessonite, rhodolite), topaz, tourmaline, spinel, tanzanite, opal, pearl, lapis, turquoise, moonstone, labradorite, iolite, zircon, chrysoberyl (including alexandrite), kunzite, hiddenite, peridot, apatite, diopside, sphene, andalusite, jade (jadeite and nephrite), coral, amber, and the major diamond simulants (moissanite, cubic zirconia, synthetic sapphire) plus lab-grown diamond.
Each gemstone record includes Mohs hardness range, refractive index range, specific gravity range, crystal system, cleavage, luster, dispersion (where significant), typical colors, common treatments, birthstone month, zodiac sign, Wikidata QID, common simulants, and source citations.
UK (London, Birmingham, Sheffield, Edinburgh, Chester closed 1962, Newcastle closed 1884, York closed 1858, Exeter closed 1883), Ireland (Dublin), France (Paris/Garantie), Italy (Vicenza as exemplar of provincial system), Sweden, Japan (Mint), India (BIS), UAE (Dubai Central Lab).
GIA, AGS, IGI, HRD, GCAL, AGL, Gübelin, SSEF, GRS, CGL, GAAJ-ZENHOKYO, AIGS, GIT, EGL, DCA.
Cycle structure metadata for London, Birmingham, Sheffield, Edinburgh, and Chester. We provide the cycle pattern (alphabet length, anniversary date, font conventions between cycles) rather than year-by-year mappings, because (a) authoritative year-letter lookup belongs in primary sources like Bradbury's Book of Hallmarks, and (b) cycle structure is what software needs to PARSE a hallmark — the year lookup is downstream of that.
See SOURCES.md for the full source list, methodology, and per-dataset provenance notes.
Primary authorities consulted include:
- ISO 9202:2019 (precious metal fineness)
- ISO 4523:2009 (gold-coating thickness)
- US FTC Jewelry Guide 16 CFR Part 23 (US labeling rules)
- UK Hallmarking Act 1973 and predecessors
- CIBJO Blue Books (Diamond, Coloured Stone, Pearl, Gemmological)
- LBMA Good Delivery Rules
- Vienna Convention on Control of Articles of Precious Metals 1972 (Common Control Mark)
- Public reference materials of: Goldsmiths' Company London, Birmingham Assay Office, Sheffield Assay Office, Edinburgh Assay Office, Dublin Assay Office, Japan Mint, Bureau of Indian Standards, Dubai Central Laboratory
- Public reference materials of: GIA, AGS, IGI, HRD, AGL, Gübelin, SSEF, GRS, CGL
- Trade press: Rapaport, JCK, GemGuide
- Standard gemological reference: Schumann's Gemstones of the World, Mindat.org
Semantic versioning by git tag. See SOURCES.md.
- Patch (X.Y.Z) — corrections, source additions
- Minor (X.Y) — new entries, new optional fields
- Major (X) — schema-breaking changes
If you use this dataset in a publication or product, please cite per CITATION.cff or:
@misc{jewelry-hallmark-reference,
author = {GradFlowLab},
title = {Jewelry Hallmark Reference: an open dataset of jewelry purity stamps, gemstones, assay offices, and gemological laboratories},
year = {2026},
url = {https://github.com/Gradient-Flow-Lab/jewelry-hallmark-reference},
license = {MIT}
}- Jewelry-identification apps and CV/OCR pipelines that map a recognized stamp to its meaning
- Marketplace listing tools (eBay, Mercari, Etsy, Vinted, Yahoo Auctions) auto-populating material fields
- E-commerce product catalogs needing consistent metal-purity metadata
- Estate-sale and auction-house cataloging software
- Insurance and appraisal tools
- Museum / collection management systems
- Educational sites and reference apps
- LLM retrieval / RAG knowledge bases for jewelry-related queries
- Academic research on hallmarking history and trade-mark evolution
PRs welcome. See CONTRIBUTING.md. All entries are validated against JSON Schema in CI; CSV mirrors must be regenerated via python3 tools/build.py and committed in-sync with JSON changes.
This dataset is maintained by the team behind Jewelry Expert AI Identifier — an iOS app that identifies gemstones, metal hallmarks, antique era, and estimated market price from a phone photo. Built by GradFlowLab.
For longer-form Japanese-language reference articles (hallmark identification, diamond authenticity, antique jewelry eras, inheritance jewelry valuation, marketplace selling), see 宝石鑑定.com/ja/learn.
MIT. Use freely in commercial and non-commercial work. Attribution appreciated but not required.