When you buy or sell a gemstone, you want to know it’s the real thing. Who wouldn’t? But how do you distinguish one gemstone from another? With tests, of course! Gemologists use a number of tools for gemstone testing. These tests measure key features including the structure, light refraction, color variation, and more. Every test offers a piece of the entire puzzle and takes you one step closer to identifying the gemstone.
If you’re interested in learning how to test gemstones yourself, we’re here to help you find the best equipment for the job. For each tool, we’ll go over how it works, the function it serves, and how to use it. Let’s start at the beginning!
Where to Start
The two crucial aspects of testing gemstones are education and practice. You don’t have to have a Ph.D. in Gemology to get an eye for identifying gems, as long as you have the knowledge and practice.
The most reputable courses come from the Gemological Institute of America, notably their Gemstone Identification Lab course. Courses are offered both in-person and online with their Distance Education program. A typical course will cost about $250. Although no one compares to GIA, there are some more affordable alternatives.
The International Gem Society (IGS) has a comparable reputation to GIA and offers mini-courses in different gemstones that are about $25 each.
And of course, you’ll find an assortment of resources and knowledge here on the Seda Gems Blog.
Have A Reference Book
Unlike the many college textbooks we never touch again, a gemstone reference book is one you’ll come back to over and over. In fact, we’d recommend it as one of your first tools for gemstone testing. To save you some time, we’ve rounded up the best three options below.
- Tables of Gemstone Identification by Roger Dedeyne and Ivo Quintens
- Internal World of Gemstones by Eduard Josef Gübelin
Alright, you chose a course, you’ve got your reference book, and you’re ready to uncover the secrets of your gemstones. Now, all you need are the tools!
Best Tools For Gemstone Testing
The first step in identifying a gemstone is getting a closer look at it. The best tool for this is a loupe.
A loupe is a pocket-sized magnifier that allows you to see details more closely. Why not use a magnifying glass instead? Well, a loupe is more portable and it has a protective cover to prevent any particles from obstructing the view. Most importantly, a smaller magnifier like a loupe gives a sharper, closer, and more accurate view. But are all loupes made the same?
Types of Loupes
- Singlet or Simple: The singlet loupe is essentially a small magnifying glass. It’s inexpensive, but the image is a bit more distorted.
- Doublet or Compound: The doublet loupe has two lenses attached together to create a bigger, sharper image.
- Triplet or Prismatic: The triplet loupe is the industry standard. It has a whopping three lenses attached together for the very sharpest view. This is the only type that corrects color, too, making it crucial for identifying a gem correctly.
The other factors to keep in mind are magnification power and size. Loupes come in 10-power, 20-power, and 30-power magnification. And the higher the power, the smaller the lens.
While having the highest power might seem like the best option, you’ll want to stick with the 10-power. Anything higher can be difficult to use because the field of view decreases and it’s harder to see the stone from different angles.
So how do you use one? First, swivel out the cover and hold the lens up to your eye. Then, hold the gem in front of the lens. You can move the gem around to see different facets or change the focus.
If you like collecting gems on your travels, consider a dark field loupe, too. It attaches to a flashlight and shows the gem’s color against a black background, lit from the side. This can make inclusions easier to spot and help you figure out if the stone is worth keeping.
Although a loupe can give you a better view of the color—a key identifier—you’ll need more tests to narrow it down. Another key identifier here is the refraction index, and there’s a gemstone testing tool for that!
Once you’ve done a visual analysis with a loupe, you’ll want to measure its refractive index with a refractometer. But what is a refractive index exactly?
A stone’s refractive index gauges the way light bends after entering it. Every gemstone’s refractive index, or RI, is constant.
For instance, both sapphires and rubies have RIs between 1.76 and 1.77 because they’re both corundum. The color, determined with your loupe or the naked eye, could help narrow down which one you have.
So how does a refractometer work? The device has a glass hemicylinder that holds the stone in refractometer fluid. With a light source, a shadow line will appear against a calibrated scale, similar to a ruler, inside. The number on the scale is your refractive index.
This is where your reference book comes in. You can narrow down the possibilities based on the visual color analysis (from the loupe) and the refractive index you just measured.
It doesn’t stop there, though. You’ll also need to examine how many colors your stone reflects with a dichroscope.
Have you ever tilted a stone and seen a different color than before? That’s because of a trait called “pleochroism,” when a gem shows different colors at different angles. A dichroscope can help determine whether a stone is pleochroic and narrow down the gemstone testing process further.
The dichroscope works by showing two colored blocks at the end of its tube. If the blocks have the same color, your gemstone is singly refractive. In other words, not pleochroic. If the blocks are different colors, you have a doubly refractive, pleochroic gemstone.
It’s important to note that not all doubly refractive gems are pleochroic. Sometimes, the variation is caused by other factors, like colored inclusions. The dichroscope can narrow these down so long as you view the stone through at least three viewing directions.
Two types of dichroscopes exist: calcite and polarizing. Calcite dichroscopes are a better option than polarizing dichroscopes, as calcite is colorless while polaroid filters have a green tint, which could distort a stone’s true colors.
Ready to Identify Gemstones? Now You’ve Got The Tools!
Gemstone identification requires patience and curiosity. Just like any science, using various testing methods provides the most accurate results. With quality tools, a good education, and lots of practice, you can test your stones right at home. Start studying, practicing with tools for gemstone testing, and soon, you’ll be an expert gemstone handler!