CENTRAL GEM LABORATORY Co., Ltd.
The Japanese trade uses CGL for diamond grading reports and for gem identification, including analytical reports on unheated corundum, jade and pearl.
The record
What it covers
Reports it publishes
Named as the laboratory names them on its own site. Report contents and wording are set by the laboratory, not by us.
- Grading Report
- Diamond Report
- Diamond Data Report
- Heart & Cupid Proportion Report
- Colored Stone Identification
- Unheated Corundum Report
- Beryllium Diffusion-Treated Corundum Analysis Report
- Paraiba Tourmaline Analysis Report
- Alexandrite Analysis Report
- Jade Analysis Report
- Pearl Layer Thickness Measurement Report
- Non-Nucleated Pearl Report
Worth knowing
The primary site is in Japanese with a reduced English section. CGL states that from November 2025 it accepts origin determination for corundum, emerald, Paraiba tourmaline and alexandrite, and that some localities are too similar for a specific origin to be stated. The diamond report lookup and the gem identification report lookup are separate tools.
Compiled from cgl.co.jp, read on August 16, 2026.
We verify dealers, not stones. A laboratory report describes one stone on one date; it is not a guarantee of value, and it is not ours to stand behind.