The open jewelry reference dataset

At a glance

License

MIT (free for commercial use)

Records

219

Datasets

6

Format

JSON · CSV · SQLite

Schema

JSON Schema validated

Linked data

Wikidata QIDs

The dataset is published on GitHub at Gradient-Flow-Lab/jewelry-hallmark-reference and mirrored here under /data/ so you can fetch any file directly over HTTPS. Source files are JSON; a CSV mirror and a built SQLite database are available in the repository.

The datasets

Six files, 219 records. Each one is downloadable from this site and from GitHub.

Jewelry hallmarks · 120 records

Purity stamps used worldwide — metal, purity, fineness, karat, region, aliases, alloy components, density, melting point, ISO reference, validity dates, and Wikidata QIDs.
Download: hallmarks.json · hallmarks.csv · GitHub

Gemstones · 49 records

Mohs hardness, refractive index, specific gravity, crystal system, cleavage, common treatments, known simulants, and birthstone / zodiac associations.
Download: gemstones.json · GitHub

Assay offices · 15 records

Current and historical assay offices — location, founding and closing dates, office mark, and operating authority.
Download: assay-offices.json · GitHub

Gemological laboratories · 15 records

The major grading labs — GIA, AGS, IGI, HRD, Gübelin, SSEF, GRS, CGL and others — with scope, founding year, and the report types they issue.
Download: gemological-laboratories.json · GitHub

Karat alloys · 15 records

Gold alloy compositions broken out per karat and per color, with the metals that make up each blend.
Download: karat-alloys.json · GitHub

British date letters · 5 records

Date-letter cycle metadata for the London, Birmingham, Sheffield, Edinburgh, and Chester assay offices — for dating British silver and gold.
Download: british-date-letters.json · GitHub

How to use it

Every file is plain JSON served over HTTPS — fetch it from anything.

# Download the hallmarks file
curl https://identifyjewelry.app/data/hallmarks.json

// Fetch and use it in JavaScript
const hallmarks = await fetch("https://identifyjewelry.app/data/hallmarks.json").then((r) => r.json());

Prefer a relational workflow? The repository ships a build step that compiles the JSON into a single SQLite database, plus the JSON Schemas that every record is validated against — so you can verify your own copy or extend the data with confidence.

How to cite

A CITATION.cff file lives in the repository. For convenience, here is a BibTeX entry and a plain APA-style citation.

@misc{jewelryhallmarkreference2026,
  title  = {Jewelry Hallmark Reference},
  author = {GradFlowLab},
  year   = {2026},
  url    = {https://github.com/Gradient-Flow-Lab/jewelry-hallmark-reference},
  note   = {Open dataset, MIT License}
}

GradFlowLab. (2026). Jewelry Hallmark Reference [Data set]. https://github.com/Gradient-Flow-Lab/jewelry-hallmark-reference

License & sources

The dataset is released under the MIT License. You may use it freely — including in commercial products — modify it, and redistribute it. Attribution is appreciated but not required.

Accuracy matters: each record cites its primary sources — ISO standards, national assay office publications, the FTC Jewelry Guides, and established gemological references — and validates against the published JSON Schemas. Wikidata QIDs are included throughout so the data slots cleanly into linked-data graphs. Found an error or have a source to add? Open an issue or a pull request on GitHub.