Gem Testing Equipment Overview
Introduction to gemmological instruments, testing workflow, and which tool to use for different identification tasks.
Introduction
Gemmological testing relies on a suite of standard instruments that measure optical and
physical properties. Mastering these tools is fundamental to gem identification and
forms the core practical skills tested in the FGA Foundation examination.
A systematic approach using multiple instruments provides the most reliable identification.
No single test is definitive—results should be correlated across several methods.
The Gemmological Toolkit
A well-equipped gemmological laboratory includes the following core instruments:
Essential Instruments
| Instrument | Primary Function | Difficulty |
|---|---|---|
| Refractometer | Measure refractive index and birefringence | Moderate |
| Polariscope | Determine optic character (SR/DR) | Easy |
| Dichroscope | Observe pleochroism in coloured stones | Easy |
| Spectroscope | View absorption spectrum | Moderate |
| UV Lamp | Observe fluorescence reactions | Easy |
| Microscope | Examine inclusions and features | Moderate |
| Chelsea Filter | Quick screening for emeralds | Easy |
Supporting Equipment
Beyond the core instruments, a complete toolkit includes:
- Specific gravity balance: For density measurement
- Thermal conductivity probe: Diamond screening
- Loupe (10×): Field examination standard
- Tweezers and stone holders: Safe manipulation
- Cleaning supplies: Cloth, brushes, solvents
- Reference materials: Master stones, comparison samples
Instrument Selection Guide
| Question | Primary Instrument | Supporting Tests |
|---|---|---|
| What is the RI? | Refractometer | SG measurement |
| Is it isotropic or anisotropic? | Polariscope | Refractometer (two readings?) |
| What causes the colour? | Spectroscope | Dichroscope, Chelsea filter |
| Is it natural or synthetic? | Microscope | UV lamp, spectroscope |
| Is it treated? | Microscope | UV lamp, spectroscope |
| What is the origin? | Microscope | Spectroscope, chemistry |
Testing Workflow
High-RI Stones
Recording and Documentation
Accurate documentation is essential for professional practice:
What to Record
For each stone examined, document:
- Date and reference number
- Description: Weight, dimensions, cut style, colour
- All test results: RI, optic character, pleochroism, spectrum, fluorescence
- Inclusions observed: With photomicrographs if possible
- Conclusion: Identification with confidence level
Professional Standards
Follow these documentation principles:
- Record observations objectively, without interpretation bias
- Note any limitations or uncertainties
- Keep equipment calibration records
- Maintain chain of custody for valuable items
- Store records securely with appropriate confidentiality