International Gemological Laboratory
GLI® Gemological Laboratories Internacional is a licensed international gemological laboratory in Pilsen, specialising in professional analysis, testing and certification of diamonds, gemstones, gold jewellery and silver jewellery. We work in cooperation with the Assay Office.
We provide expert gemological reports, identification and assessment of precious stones using state-of-the-art instruments and international standards. All expertises are conducted exclusively in person based on a thorough physical examination.
We Buy & Sell
sapphires · rubies · emeralds · diamonds · gold · silver · jewellery
Our Services and Prices
For larger quantities, prices are determined individually in agreement with the gemologist.
Diamond Expertises
- Natural diamonds
- Treated diamonds
- Laboratory-grown diamonds – CVD & HPHT
- Moissanites
- Diamond simulants
- Appraisal
Full assessment using the 4C system (Color, Clarity, Cut, Carat) including a clarity diagram.
Loose diamonds from 0.20 ct, colour range D–J. Set stones from 1.8 mm.
| Service | Price |
|---|---|
| Test report without certificate | €28 |
| Test + diamond certificate | €69 |
| Test + certificate + security blister | €101 |
Gemstone Expertises
- Natural gemstones
- Heated gemstones
- Unheated gemstones
- Synthetic gemstones
- Treated or otherwise enhanced stones
- Appraisal
Rubies, sapphires and emeralds – determination of authenticity, origin and possible treatments.
| Service | Price |
|---|---|
| Test report without certificate | €28 |
| GLI gemstone certificate | €69 |
| Test + certificate + security blister | €101 |
Gold & Silver Expertises
- Visual examination under gemological microscope
- Digital spectrometer analysis
- Reference testers 2026/2027
- Appraisal
Professional testing of gold and silver including full jewellery analysis.
| Service | Price |
|---|---|
| Test report without certificate | €28 |
| Certificate of authenticity | €69 |
GLI® Certificate
GLI® Gemological Laboratories Internacional issues independent gemological certificates confirming the authenticity, quality and properties of a gemstone, diamond or piece of jewellery in accordance with internationally recognised standards.
- Detailed gemological report
- Stone identification
- Photograph (with selected services)
- Online certificate verification code
Security Blister
Professional encapsulation into a tamper-evident security box with certificate. Protects the stone from damage, enables safe storage and preserves certification. Also suitable as gift packaging. Substitution is not possible.
Gemstone Treatments
During analysis we identify any treatments and enhancements that may affect a stone's value. Note – some gemstones may become toxic after certain treatments.
Heat Treatment
Temperatures of 800–1800 °C to improve colour and clarity. Widely accepted in the jewellery trade.
Fracture Filling
Used to fill cracks and increase transparency. Agents include cobalt and beryllium.
Lead Glass Filling
Applied to heavily fractured stones to improve appearance (PB glass, borax).
Surface Diffusion
Chemical elements penetrate the surface of the stone and alter its colour.
Oiling & Dyeing
Temporary enhancements used to improve colour and transparency, typically in emeralds.
Modern Gemological Equipment
Our laboratory uses professional instruments employed in modern gemology, operating in parallel with AI.
- Gemax Trinocular Gems Stereo Microscope, LCD PC
- Gemologis PRO CVD Tester – lab-grown diamond detection, spectrometer
- Gemax Polariscope
- UV Light Box Professional LW/SW
- Refractometer – refractive index measurement
- GIA FacetWare Software
- Ayaz light gem, Switzerland XLR1 Gems, Gem master RI liquid, Grobet USA, Radwag gemologic, gemstone gripper
- Gem pads, diamond sieves, ultrasonic cleaner, Gemax electronic gauges, Presidium gauges, diamond master set, Presidium gem tester
Visit Us or Send Your Stones
Opening Hours
Daily 9:00 AM – 9:00 PM
Zlatnický dům, OC Plaza Pilsen
Radčická 2, 301 00 Plzeň
→ View on map
Sapphires, rubies, emeralds, diamonds and jewellery may also be sent by registered post as insured valuable correspondence.
Consultation with a Gemologist
For a personal consultation, please book an appointment in advance:
Express services are available subject to laboratory capacity and an additional fee. The order of analyses is determined by the gemologist.