The tools on this site are our own software. The ideas behind them are not. This page lists the people and publications they rest on, and the open-source components they are built from.
The round brilliant: Tolkowsky, 1919
Marcel Tolkowsky, Diamond Design: A Study of the Reflection and Refraction of Light in a Diamond (London: E. & F. N. Spon, 1919). The first worked calculation of round brilliant proportions from the path of light through the stone. The crown and pavilion angles it arrived at are still the reference point for every proportion we grade against. Our name takes its year.
The physics in the ray tracer
- Reflection and refraction at each facet follow Snell's law and the Fresnel equations (Augustin-Jean Fresnel, 1820s). Light that meets a facet from inside the stone at a shallow enough angle is reflected entirely; this is what makes a diamond bright.
- Dispersion, the splitting of white light into colours, comes from the refractive index of diamond changing with wavelength. We use a Sellmeier-form fit of diamond's index across 400–700 nm (Wilhelm Sellmeier, 1871) and trace several wavelengths per ray.
- Colour on screen is produced from the traced wavelengths with the CIE 1931 colour-matching functions.
Light-performance research
- José M. Sasián, Jason Quick, Jacob Sheffield, James Caudill and Peter Yantzer, "Evaluation of brilliance, fire, and scintillation in round brilliant gemstones", Optical Engineering 46(9), 093604 (2007), doi:10.1117/1.2769018. This peer-reviewed paper describes mapping which directions of incoming light a stone returns to the viewer, and why proportions near Tolkowsky's perform well. Our Light return map is our own implementation of that idea: light arriving from each band of angles is given a colour, and the picture shows which facets return it.
- José Sasián, Peter Yantzer and Tom Tivol, "The Optical Design of Gemstones", Optics & Photonics News, April 2003. An introduction to the same approach.
- T. S. Hemphill, I. M. Reinitz, M. L. Johnson and J. E. Shigley, "Modeling the Appearance of the Round Brilliant Cut Diamond: An Analysis of Brilliance", Gems & Gemology 34(3), 1998. An earlier computer model of brilliance across a range of proportions.
The ASET® idea and who invented it
The three-colour angular map was developed by the American Gem Society Laboratories' cut-grading research team, with José Sasián of the University of Arizona and Peter Yantzer, and is sold by the American Gem Society as the Angular Spectrum Evaluation Tool, ASET®. The instrument was covered by US patents 7,372,552 and 7,382,445 (filed December 2004), which public records show as expired; the computer-generated versions of the map are covered by US patents 8,098,369 and 9,599,570, held by the Gemological Institute of America and still in force. We credit that work here, and it is why the public viewer on this site does not compute such a map: the light-return pictures of our stones are made in advance in Singapore. We are not affiliated with, endorsed by or licensed by the American Gem Society or the Gemological Institute of America; see Legal notices.
Hearts and arrows
The hearts-and-arrows viewer, a dark tube with a bright ring of light around the eyepiece, was described in European patent application EP 0412168 A1 (1989). Trade sources credit Kinsaku Yamashita with its development. Our Hearts and arrows view models that geometry: a bright band from about 4° to 15° off the viewing axis and a dark wall beyond it, which is what makes the pattern appear.
What our own work adds
- A ray tracer written for this site. On the Compare & viewer page it runs on the graphics processor of your own device, so the side-by-side comparison is computed live from the two certificates. The pictures and loops on each stone's page are made by the same ray tracer in advance, on our machines in Singapore, when the stone is listed.
- A grading model that reads the proportions printed on an IGI certificate, checks them against hard gates, and scores the stone. The gates and scoring are ours. They are described in How we grade.
- The studio, spotlight and worn lighting set-ups, the precession motion, and the flash map.
Open-source software used on this site
- pdf.js (Mozilla), Apache License 2.0 — reads the text of certificate PDFs in your browser.
- tesseract.js, Apache License 2.0 — reads certificate pictures in your browser.
- JSZip, MIT License — packs files for download.
- mp4-muxer, MIT License — writes the precession videos.
- Inter typeface (Rasmus Andersson), SIL Open Font License 1.1.
Nothing you drop into the tools leaves your browser. Certificates are read on your device; the site never contacts a grading laboratory.