Presidium Gem Tester II (PGT II) Coloured Gemstone Tester
Brand: Presidium Instruments
The Presidium Gem Tester II (PGT II) helps assess suspected gemstones by measuring their thermal conductivity. Its analogue dial shows possible gemstone ranges, supporting further identification alongside other gemmological checks.
Understanding the limits
The PGT II is a testing aid and should not be relied upon as the sole means of identification. Some gemstones share overlapping readings. It cannot distinguish diamond from moissanite, or natural gemstones from their synthetic counterparts, including natural and laboratory-grown diamonds. Further tests are needed to confirm identity or origin.
Features
- Thermal conductivity testing for a range of common coloured gemstones.
- Analogue display showing possible gemstone ranges.
- Fine 0.6mm retractable probe tip.
- Built-in Glass and Calibration (CAL) reference discs.
- Audible alert when the probe touches metal.
- Suitable for polished and unpolished gemstones where proper probe contact can be made.
- Powered by two AA batteries or a compatible Presidium mains adaptor.
🎥 See the Product in Action
See the tool in action before reading the full specification.
Watch the PGT II demonstration on YouTube.
Before and during testing
- Connect the probe before switching on. Allow the warm-up period specified in the handbook for your unit.
- Check the Glass and CAL reference discs using the handbook instructions.
- Test clean, dry stones after they have adjusted to room temperature. Presidium recommends 18 to 27°C.
- Hold the probe perpendicular to a suitable facet, away from the setting. Use only enough pressure to retract the tip fully.
- Read the highest needle position. Take several readings, allowing very small stones to cool between tests, and consider every gemstone range crossed by the needle.
PGT II quick help and FAQs
Select a question to see the answer.
Before testing
- Connect the probe with the unit switched off, then allow the handbook warm-up period.
- Check the CAL and Glass reference readings.
- Use clean, dry stones that have reached room temperature.
Do I need to adjust calibration at every startup?
Check the reference readings after warm-up. Adjust calibration only as directed in the matching handbook, such as after a probe replacement or incorrect reference readings.
How should I clean a stone?
- Start with a clean, soft cloth containing no polishing compounds. Avoid silver-polishing cloths.
- For suitable items, use lukewarm water and a very soft brush. Dry thoroughly before testing.
- Unsure about the stone, treatment or setting? Ask for advice before wet cleaning, solvents, steam or ultrasonic cleaning.
Understanding results
Readings indicate possible identities. Overlapping ranges need further tests.
Does a diamond-range reading prove it is diamond?
No. Diamond and moissanite can give similar readings. Further testing is needed to separate them.
Can it separate natural and laboratory-grown stones?
No. The PGT II cannot establish natural or laboratory-grown origin, including for diamonds.
Troubleshooting
Why do readings vary?
- Recheck power, reference readings, cleanliness and temperature.
- Use the probe contact and pressure described in the handbook.
- Allow very small stones to cool before repeating tests.
Why is the metal alert sounding?
The probe may be touching the setting or another metal surface. Reposition it onto the gemstone and repeat the test.
What if the reference checks still fail?
Follow the matching handbook's calibration instructions. If checks still fail or the probe appears damaged, contact Walsh before relying on further readings.
Email the H.S. Walsh team at [email protected] for demonstrations, troubleshooting or repair enquiries. Quote PGT II / TD53.
User handbooks and documents
Download the PGT II user handbook in the following languages from the Related files tab on this page:
- English (PDF in Related files)
- Spanish / Español (PDF in Related files)
- German / Deutsch (PDF in Related files)
The certificate of conformity is also available in Related files.
Other handbook languages
Handbooks are also available on request in Chinese / 中文, French / Français, Italian / Italiano, Russian / Русский.
To request a handbook, email the H.S. Walsh team at [email protected] and tell us which language you need. Please quote PGT II / TD53.
Further help
For help with setup, testing technique or unexpected readings, contact H.S. Walsh and quote product code TD53.
