For colored stones, buy a tester to support an identification process rather than to supply a guaranteed name for every unknown gem. Gold Kings would begin with the Presidium Gem Tester II for a defined thermal-screening role and consider the Duo Tester II when its additional measurement will be used.
Decide which question matters
“Could this be glass?” is different from “Is this natural ruby?” A device useful for narrowing the material possibilities may not establish natural origin or detect a treatment.
Write down the questions you need answered before comparing models. That makes it easier to see whether a feature actually helps or simply makes the specification list longer.
Compare the methods
The Gem Tester II uses thermal conductivity. The Duo Tester II adds reflectivity measurement to thermal screening.
A reading can overlap with more than one possible material. Interpret it alongside other observations instead of treating the nearest printed name on a dial as a complete identification.
Presidium states that these instruments do not distinguish natural from synthetic colored gemstones. That limitation matters if origin is central to the buying decision.
Match the device to the stones
Consider whether your stones are loose or mounted, whether a suitable test surface is accessible and whether the instrument’s sample requirements can be met.
For the Duo, specifically check the reflectivity procedure. Do not assume that every stone you can touch with the thermal probe can also be measured correctly using the second method.
Ask for a demonstration that resembles your actual work, including how the operator records an uncertain result.
Budget for supporting tools
A suitable loupe, careful handling tools and a good inspection light can make the tester easier to use. Reference material and training help you interpret what you see.
For valuable unknown stones, allow for professional identification as part of the overall cost. A cheaper instrument is not a saving if it encourages an unsupported purchase claim.
Our recommendation
Choose the Gem Tester II when you want a straightforward thermal screening step. Consider the Duo Tester II when you understand the extra method, have suitable samples and will use the added information.
If your main question concerns natural origin, treatments or a high-value attribution, arrange qualified gemological testing. The best purchase is the tool that answers the right part of the question, with a clear plan for what remains unresolved.
Explore the relevant products
- Presidium Gem Tester II PGT II Thermal Gemstone Tester
- Presidium Duo Tester II PDT II Gemstone Screening Instrument
Check the exact model, seller, package contents and current offer on the linked product page before ordering.
Sources and further reading
Explore more Gold Kings buying guides.
As an Amazon Associate I earn from qualifying purchases. The product pages linked in this article contain Amazon affiliate links. This guide is based on published specifications and practical buying considerations, not a controlled hands-on product test.