This is not a paid promotion. I am a UK-based antique dealer, and I personally purchased this gem tester for both business and personal use. This is my honest review of the product, where I’ll explain what it is, why you might need it, and how it can not only save you a significant amount of money but also help you make a substantial profit.
What is the Presidium Gem Tester?
The Presidium Gem Tester is a scientific instrument designed to identify gemstones by measuring their thermal conductivity. It works using a handheld probe with a copper nib at the tip. When this nib makes contact with a gemstone, the device measures how quickly heat is drawn away from the probe. Different gemstones conduct heat at different rates, allowing the tester to accurately identify the type of stone you’re examining.
This straightforward yet effective method makes the Presidium Gem Tester a valuable tool for both professionals and hobbyists, eliminating much of the guesswork involved in gemstone identification without the need for advanced gemology knowledge.
Understanding the Thermal Conductivity Testing Process
The Presidium Gem Tester II operates by measuring the thermal conductivity of gemstones — essentially, how quickly a material draws heat away from a heated probe. The device uses a fine copper nib that gently heats up when in contact with a stone. As the stone draws heat from the nib, the tester measures the rate of heat transfer and displays the result on its dial.
Different gemstones conduct heat at different rates, which allows the machine to distinguish between materials like glass, quartz, sapphire, and diamond. For example, diamonds, being composed of pure carbon, have exceptional thermal conductivity and quickly draw heat away from the nib, sending the needle into the “diamond” section on the display.
However, this process has its limitations. Moissanite, a popular diamond simulant, conducts heat at a rate similar to diamonds, often producing identical readings. For this reason, users may need an additional tool — such as a diamond/moissanite tester — to confirm results when the tester indicates a diamond.
Understanding this underlying principle helps you get more reliable results from the machine and avoid misidentifying high-quality simulants as precious stones. Clean, dry stones will yield the most accurate readings, while dirt or grease can interfere with heat transfer and skew results.
Why Would You Need A Gem Tester?
To explain why a gem tester can be essential, let me share a bit about my experience. As a UK-based antique dealer, I spend a lot of time at flea markets, yard sales, car boot sales, and auction houses, hunting for antiques, collectibles, and jewelry. While I can easily identify whether a ring is gold or sterling silver, I’ve often struggled to identify the gemstones set within the jewelry. For years, I relied on jewelers to identify and value these stones — a process that was both time-consuming and costly. I simply didn’t have the time to study gemology, so investing in a gem tester was the logical next step.
If you’re in a similar position, you really have three choices:
- Pay a jeweler to identify each gemstone — a recurring expense that quickly adds up.
- Buy a gem tester to handle the identification yourself, saving both time and money.
- Sell jewelry without identifying the stones — for example, listing an item as a ‘9ct yellow gold dress ring’ without specifying the gemstones. While this approach may seem simpler, it often results in lower sale prices, and guessing can lead to returns and unhappy buyers.
For anyone dealing with second-hand or vintage jewelry, knowing exactly what stones you have is crucial. It not only helps maximize your profits but also builds buyer confidence by providing accurate descriptions.
Need To Know Gems.
For antique dealers, knowing which gemstones are set in our jewelry is essential for providing accurate descriptions and determining a fair market value. An accurate identification not only helps establish trust with buyers but also ensures you don’t leave money on the table when pricing your pieces.
In the past, I always had to rely on jewelers to identify the gemstones in my finds. The cost of these valuations varied depending on the jeweler and location. Some charged a flat fee, while others took a percentage of the item’s value. On average, it could cost anywhere from £20 to £30 just to confirm the stones in a single ring or necklace — and when you deal with multiple pieces regularly, these costs quickly add up.
This is where the Presidium Gem Tester comes in. If it performs as promised, it can identify gemstones accurately from the comfort of your own home. That means no more repeated visits to the jeweler and no more ongoing fees — just straightforward gemstone identification whenever you need it. Over time, the machine has the potential to pay for itself while giving you more control over your business.
How to Value gems?
Once the Presidium Gem Tester helps you identify the gemstones in your jewelry, the next step is determining their value. Pricing jewelry accurately requires a combination of understanding the materials involved and researching the market.
For instance, if you have a ring made of 9ct gold with a large amethyst and small diamond chips, you can begin by looking for comparable items on popular selling platforms. While diamond chips don’t significantly increase value unless they reach around half a carat or more, a well-cut amethyst can still add appeal and boost the final price.
Understanding Base Value:
Jewelry always has a baseline value derived from the precious metal content, known as the scrap or spot price. This value fluctuates daily with the stock market, so it’s essential to check updated rates regularly.
As an example, on August 21, 2020, the spot price for 9ct gold was approximately £18 per gram. If your amethyst ring weighs six grams, you’ll need to deduct the stone’s weight — leaving around 5.5 grams of gold. At that time, the base value for the gold alone would be around £90. From there, you can add the gemstone’s value and any additional premium for the ring’s design or age.
This process is exactly why I invested in the Presidium Gem Tester. Knowing which gemstones you’re dealing with allows you to price more accurately, maximize profits, and avoid undervaluing pieces that could be worth far more than just their gold content.
The Presidium Gem Tester Review
How much does the gem tester cost?
I had my eye on the Presidium Gem Tester for a couple of years before finally purchasing one. For a long time, I struggled to find a seller in the UK. While the testers were available overseas, the additional costs of tracked shipping and customs duties made the purchase a risky gamble — especially without knowing whether the machine would perform as expected.
However, this year I noticed they became more accessible in the UK. I eventually purchased mine on eBay, though they might also be available on Amazon or other platforms. When I checked the market at the time, I found only two listings: one priced at over £400 and the other at approximately £250 — quite a significant price difference for the exact same product. I ended up paying £300 for mine, and to my surprise, the same seller increased the price to £500 just a week later.
Given the average cost of a mini valuation is around £20 per item, I calculated that the gem tester needed to successfully test at least 25 pieces to break even — a target I expected to reach within a month. However, for part-time resellers or those with smaller inventories, this break-even point might take a year or more to achieve. For this reason, durability and reliability were key factors for me when deciding to invest in the Presidium Gem Tester.
A Look At The Presidium Gem Tester II
The Presidium Gem Tester arrives well-presented in a sturdy, professional-looking box. Inside, you’ll find a protective pouch with a secure zip closure, perfect for storing the device safely when not in use. This added layer of protection is particularly useful if you plan to take the tester to markets or appraisal appointments.
The tester can be powered in two ways: either by two AA batteries or via the included mains power lead. However, it’s worth noting that the provided plug is a two-prong design, so if you’re in the UK, you’ll need a simple adapter to use it with local sockets. Along with the power lead, the package includes a detailed instruction manual and two warranty cards. If you opt to use batteries, make sure to choose a high-quality brand and remove them during extended periods of inactivity to prevent potential acid damage — an essential step when dealing with sensitive, expensive equipment.
The device itself is surprisingly lightweight, making it easy to carry and use on the go. Setup is refreshingly simple: the pen-like probe plugs into the back of the unit alongside the power lead, and the machine comes factory-calibrated, eliminating the need for any complicated adjustments. There’s no requirement to have specific gemstones on hand to get it ready for use.
Once powered on, you’ll see a red light indicating it’s ready for calibration. To calibrate, simply press the probe firmly against the Cal pad, ensuring the nib is fully depressed. The needle should move to the Cal position on the display. Next, press the probe on the glass pad; the needle should align with the Glass mark. If both steps go smoothly, you’re ready to start testing your gemstones.
This was all the setup that was needed and to be honest, was perfect for me, I need simple to use and not too complicated.
Battery vs. Mains Power Usage
The Presidium Gem Tester II offers two convenient power options: battery operation or mains power. Understanding how to use both effectively can help you get the most reliable performance from the device.
1. Battery Power for Portability
The tester can run on two AA batteries, making it highly portable — perfect for taking to antique fairs, markets, or auctions. However, for accurate and consistent results, it’s essential to use high-quality alkaline batteries. Low-quality or partially drained batteries may cause the nib to heat unevenly, leading to inaccurate gemstone readings.
Tip: If you’re not planning to use the device for an extended period, remove the batteries to prevent corrosion. Battery acid leaks can damage the internal components and significantly shorten the lifespan of the tester.
2. Mains Power for Consistent Use
For those who plan to use the tester regularly in a workshop or home setting, mains power is the more reliable choice. The device comes with a power cable, but it uses a two-prong plug, which is standard in many European countries.
Important: If you’re based in the UK, you’ll need a simple plug adapter to fit British sockets. These adapters are inexpensive and easy to find, but it’s a small detail that can cause frustration if overlooked when setting up the device for the first time.
By choosing the right power source for your needs and taking care of the batteries, you can ensure that your Presidium Gem Tester II remains accurate and reliable for years to come.
Testing Gems.
With the gem tester calibrated and ready, it was time to put it to the test. I documented the process in a video, which you can watch below.
For my initial tests, I used various pieces of jewelry I had on hand:
- A ring set with amethyst and diamond chips.
- An 18ct gold ring with a tourmaline centerpiece.
- A classic diamond solitaire.
- And finally, some glass and paste stones set in sterling silver.
The testing process was straightforward. I simply held the probe against each stone, ensuring the nib was fully depressed. It’s important to remember that gemstones should always be clean and dry before testing, as dirt or moisture can interfere with the accuracy of the readings.
The beauty of this device is that stones can be tested while still set in their jewelry or when placed directly on a testing plate, giving it a level of flexibility that’s incredibly convenient for dealers and collectors alike.
The Need for a Gem Color Chart
While the Presidium Gem Tester II does a great job at identifying gemstones through thermal conductivity, certain challenges arise when dealing with stones that share similar physical properties. Gemstones like garnet, spinel, and ruby, for example, can produce readings in the same range due to their comparable heat conductivity, especially when they’re similar in color. This overlap can make it tricky to confidently identify a stone based solely on the device’s reading.
One potential improvement would be for the manufacturer to include a comprehensive gemstone color chart with the product. Such a chart could display the possible colors for each gemstone and indicate where each would likely fall on the tester’s scale. This visual reference would help users narrow down their findings more accurately without the guesswork.
From my own experience, I’ve found this lack of guidance somewhat limiting, particularly when testing stones with less obvious characteristics. As a result, I’m considering creating my own gemstone color chart to simplify the process. Once complete, I plan to share it on my blog so that others can benefit from a clearer understanding of which colors to expect for various gems.
Until then, my advice is to combine the tester’s results with visual inspection and other clues — such as the stone’s cut, setting, and overall appearance — to improve your identification accuracy. With some practice and the right resources, this limitation becomes more manageable.
Practical Applications for Dealers
For antique dealers, jewelry resellers, and collectors, the Presidium Gem Tester II isn’t just a gadget — it’s a powerful tool for maximizing profits and ensuring accurate, trustworthy listings. Correctly identifying gemstones can make a significant difference when it comes to pricing and marketing jewelry. Here’s how the tester can benefit dealers in practical, day-to-day operations:
1. Accurate Descriptions Prevent Returns
When selling jewelry, accuracy matters. Describing a piece as a “9ct gold dress ring with a blue stone” leaves buyers uncertain about the stone’s true value. If a customer purchases the item expecting a sapphire only to find it’s glass, you could face a costly return. The Presidium Gem Tester II helps avoid this issue by providing reliable gemstone identification, enabling you to list items with confidence.
2. Gemstone Identification Can Double the Value
Jewelry with verified gemstones consistently sells for more than pieces described vaguely. For instance, a 9ct gold ring listed simply as a “dress ring with red stones” might attract scrap-level offers. But if you can identify those stones as garnets, rubies, or spinels, the perceived value increases significantly. In some cases, gemstone identification can double or even triple the sale price.
3. “Gem-Tested” Listings Build Buyer Trust
Adding the phrase “Gem-Tested with Presidium Gem Tester II” to your listings assures buyers that you’ve taken steps to accurately identify the stones. This small addition can build trust, especially on platforms like eBay, Etsy, or private sales websites, where authenticity is often a concern. Buyers are more likely to purchase from sellers who demonstrate professionalism and product knowledge.
4. Saves Time and Money Long-Term
While the tester requires an upfront investment, it quickly pays for itself. Regularly visiting a jeweler to identify stones costs both time and money — often with fees ranging from £20 to £30 per item. By identifying gemstones independently, you save on these recurring expenses and avoid the hassle of booking appointments and waiting for results.
In the competitive world of jewelry resale, knowledge equals profit. The Presidium Gem Tester II provides that knowledge, helping dealers make informed decisions, avoid misidentifications, and boost customer confidence.
Unexpected Discoveries and User Learning Curve
Using the Presidium Gem Tester II isn’t just about confirming what you already suspect — it can also lead to some surprising discoveries. During my testing, I came across a few unexpected results that highlighted the tester’s potential as well as the importance of practice and patience.
1. Surprising Finds in Everyday Jewelry
While testing a ring I originally assumed was set with inexpensive costume stones, I discovered that the pink stones were actually rubies and the purple stones were genuine amethyst. This kind of revelation can significantly impact the value of a piece. What might have been sold as a simple gold dress ring turned out to be a far more valuable item with authentic gemstones.
This experience reinforced just how often valuable stones can go unnoticed, especially in vintage or mass-produced jewelry where assumptions about materials are common. With the gem tester, those hidden treasures become much easier to spot.
2. Practice Makes Perfect
While the tester is relatively easy to use, it does have a learning curve. It takes practice to correctly position the nib on the stone without accidentally touching the metal setting, especially when dealing with smaller stones like diamond chips. Misreads can happen if the nib makes contact with the metal, causing confusion and frustration if you’re unfamiliar with the tester’s behavior.
3. Learning Stone-Specific Patterns
As you use the tester more frequently, you’ll start to notice patterns. For example, gemstones like garnet, spinel, and ruby can display similar readings due to their shared thermal characteristics. Over time, you’ll become better at interpreting results by considering additional factors like color, clarity, and context.
Patience and practice are essential, but the rewards are well worth it. The Presidium Gem Tester II can transform the way you identify and value jewelry, helping you uncover hidden gems — sometimes literally — in your collection.
Common Testing Challenges and Tips
While the Presidium Gem Tester II is a straightforward and user-friendly tool, there are a few challenges you might encounter when testing gemstones. During my own experience with the tester, I came across several practical insights that could help you get more accurate and reliable results.
1. Ensure Stones Are Clean and Dry
Thermal conductivity testing relies on the heat transfer between the nib and the stone’s surface. Dirt, grease, or moisture can act as insulators, disrupting this process and leading to inaccurate readings. Before testing, take a moment to clean each gemstone with a lint-free cloth and ensure it’s completely dry.
2. Testing Small Stones Can Be Tricky
The tester’s nib requires full contact with the stone to provide an accurate reading. When dealing with very small gemstones, especially diamond chips, it can be difficult to position the nib without touching the surrounding metal. If the nib makes contact with the setting, the tester may give a false reading or emit an error sound. For tiny stones, try using tweezers to hold the jewelry at an angle that minimizes the risk of nib-to-metal contact.
3. Interpreting Ambiguous Results
Certain gemstones, like garnet and tourmaline, share similar thermal conductivity ranges, which can cause confusion. If the tester’s needle hovers between two categories, consider the stone’s color, clarity, and the type of jewelry it’s set in. For example, a deep red stone in a vintage gold ring is more likely to be garnet than tourmaline.
4. When in Doubt, Recalibrate
The Presidium Gem Tester II comes factory-calibrated, but it’s essential to recalibrate occasionally to maintain accuracy. Use the Cal and Glass reference points as instructed in the manual. If readings seem consistently off, consider testing known stones to verify the machine’s accuracy.
5. Distinguishing Diamond from Moissanite
One limitation of the Presidium Gem Tester is its inability to differentiate between diamond and moissanite, as both materials conduct heat at similar rates. If your tester indicates a diamond but you have doubts, a separate moissanite tester — available for around £8 online — can provide more clarity.
By following these tips and familiarizing yourself with the tester’s behavior, you’ll reduce guesswork and improve the reliability of your gemstone identifications.
My Conclusion.
Based on my experience, I believe the Presidium Gem Tester II delivers on its promises. It did exactly what I needed it to do: identify gemstones accurately, efficiently, and with minimal effort. While the initial cost is on the higher side, it has proven to be a worthwhile investment. For anyone regularly dealing with jewelry, the tester should pay for itself in a relatively short time, especially when you consider the savings from no longer needing to hire a jeweler for basic stone identification. The build quality also gives me confidence that it will last for years to come.
That said, there is room for improvement. I feel the manufacturer could enhance the product by including a gemstone reference chart, displaying both the colors and the corresponding readings for different stones. Since certain gemstones share similar thermal conductivity, having a guide like this would make it easier for users — especially beginners — to narrow down the possibilities and confirm their findings more confidently.
Overall, I’m happy with my purchase. This review is based entirely on my personal experience with a product I bought for my own use — it is not a paid promotion. I hope you found my insights helpful, and if you’re considering investing in a gem tester, this one might just be what you need.”
Recommended Resources for Gem Identification
1. Gem Identification Made Easy: A Hands-On Guide to More Confident Buying & Selling
- Authors: Antoinette Matlins, Antonio C. Bonanno
- ISBN: 978-0757000983
- Overview:
This book is perfect for beginners and professionals alike. It offers step-by-step instructions on identifying gems using simple, inexpensive tools — including thermal conductivity testers like the Presidium. It covers both natural and synthetic stones, helping dealers avoid costly mistakes.
2. The Complete Color Encyclopedia of Gemstones
- Author: Joel E. Arem
- ISBN: 978-0442236515
- Overview:
A classic reference guide, this book features detailed information on hundreds of gemstones, including their physical properties, origins, and identification methods. The clear color photographs make it an invaluable resource for visual comparison when identifying stones.
3. Gems: Their Sources, Descriptions and Identification
- Author: Michael O’Donoghue
- ISBN: 978-0750658563
- Overview:
This comprehensive guide is widely respected in the gemology field. It covers gem materials, treatments, and synthetic stones in detail, making it a useful resource for anyone working with both antique and modern jewelry.
4. Handbook of Gem Identification
- Author: Richard T. Liddicoat
- ISBN: 978-0873110196
- Overview:
Liddicoat, a key figure in modern gemology, provides an in-depth look at gemstone testing techniques. The book discusses thermal conductivity, refractive indices, and other key identification methods, making it particularly useful for those using tools like the Presidium tester.
5. Practical Gemmology: A Study of the Identification of Gemstones
- Author: Robert Webster
- ISBN: 978-0719803611
- Overview:
This practical guide focuses on the fundamental skills required for gemstone identification. It explains various testing methods, including thermal conductivity, and is an excellent companion for anyone regularly testing stones for resale.
