10 Best Diamond Testers 2025 in the United States

The HMKIS Diamond Tester Pen is designed for both novices and experts who need to verify the authenticity of diamonds quickly and accurately. One of its standout features is the dual power supply option, allowing users to choose between a Type-C or a 9V power source, which enhances accuracy and stability. The tool is user-friendly, requiring no professional knowledge to operate; users simply select the diamond size and place the tester on the gemstone. The audible signals and LED indicators make interpreting results straightforward, which is great for anyone needing quick assessments.

Portability is another strong point, as the device is lightweight (120 grams) and compact, making it easy to carry for on-the-go testing. Additionally, the inclusion of a 60X LED Jeweler's Loupe enhances its functionality, allowing for detailed inspections of not just diamonds, but also various collectibles and antiques.

The HMKIS diamond tester requires careful handling; incorrect use, such as not touching the panel or testing unsuitable items, can lead to inaccurate results. Users must also ensure they select the correct diamond size before testing, which could be a minor hassle for some.

The Presidium Instruments Gem Tester II (PGT II) is a solid choice for anyone needing a reliable diamond tester, particularly hobbyists and professionals in the jewelry field. One of its standout features is the Assisted Thermal Calibration (ATC), which allows users to calibrate the device easily to their environment, enhancing accuracy in testing. This model is designed to be compact and portable, making it easy to transport, which is a significant advantage for gemologists on the go or those attending trade shows.

The tester is simple to operate, featuring a clear analog dial that can differentiate between 16 types of gemstones, including diamonds and moissanites. This ease of use is beneficial for those who may not be very tech-savvy, as it keeps the testing process straightforward.

There are some drawbacks to consider. Despite its user-friendly design, calibration issues can arise during shipping, which may require assistance from the manufacturer. Additionally, the reliance on AA batteries may be seen as a minor inconvenience for some, as it requires regular replacements. While it generally delivers consistent and reliable results, the quality can vary slightly based on calibration and user proficiency. Being aware of this can help manage expectations.

The Valkynos Professional Diamond Tester Pen is a handy tool designed for anyone who wants to quickly check if a diamond is real, whether you're a beginner or more experienced. It uses thermal conductivity to test gems and gives results in just half a second, which is impressively fast. It can accurately identify diamonds as small as 0.02 carats, making it useful for a range of stones. A nice extra is the built-in UV light that helps spot diamond fluorescence, adding another layer of verification. This is something not all testers offer and can help catch fakes that might slip through thermal testing alone.

The tester is straightforward to use: after a short warm-up, you hold the pen properly and look for a red light and buzzer sound to confirm a genuine diamond. Just keep in mind it works best at room temperature and with bare hands, so following these tips will improve accuracy. The device is lightweight and compact, coming with a protective pouch, so it’s easy to carry around for quick checks on the go—great if you travel or visit jewelry stores.

Regarding battery life, it runs on a 9V battery included in the package, which should last a reasonable amount of time, but replacements are easily available. One limitation is the need for a warm-up period of about 25 seconds before testing, which is a bit slower than some instant-read testers. Also, while it is accurate and reliable for diamonds, it may not distinguish every type of gemstone or synthetic diamond perfectly. This diamond tester pen offers a good balance of speed, accuracy, and useful features like UV fluorescence detection, all in a portable design. It’s best suited for casual users, collectors, or small-scale sellers who need a dependable and easy-to-use device without the complexity of professional lab equipment.