Posted on November 11, 2015 by

How to Use a Loupe: The Guide to Grading Diamonds Like a Pro


A diamond loupe is a gemologist’s best friend. If you’re new to the world of diamonds and diamond jewelry, the first thing you’ll want to familiarize yourself with – perhaps even before getting a basic understanding of The Four Cs – is knowing how to use a loupe. This skill, more than any other, can mean the difference between walking out the door with a straightforward jewelry purchase in hand or being fabulously ripped off. Today we give a handy lesson on how to use a loupe – and what exactly a loupe is.




Jeweler looking at loose pink diamond through loupe

If you prefer, you can also hold your loupe by grasping onto the frame with your index finger and thumb.


How to Use a Loupe

What is a Loupe?


A loupe (pronounced “loop”) is a small hand-held magnifier that allows for the examination of small details in and on diamonds, gemstones and jewelry. Gemologists and jewelers typically use a loupe with 10X magnification to view details of diamond clarity and to do their diamond grading. Anything with higher magnification, such as 20X or 30X, will make the gemstone or jewelry harder to view through the loupe because it causes a smaller field of view and depth of field. Field of view is the area that is visible through the loupe while depth of field refers to the area that is in focus as the loupe is moved toward or away from the item being observed. Diamond loupes can be folded into a protective cover that doubles as the handle.


A loupe will usually have three kinds of lens with a diameter of either 18 millimeters or 21 millimeters combined to correct distortion and color issues. This kind of loupe is known as a “triplet.”


How Do You Use a Loupe?


Jeweler holding loupe for diamonds

Step #1: Hold your loupe by “unfolding” it (i.e., sliding it out) from the protective cover and slipping the index finger on your dominant hand through the opening while bracing the back of the loupe “handle” (protective cover) against your middle finger.


Unfold the loupe from the protective cover. Slide your index finger through the opening and brace the back of the loupe handle against your middle finger. Your dominant hand should be the one holding the loupe as it will align with your dominant eye to view the item. For many, if not most, people, they will use their right hand to grasp the loupe while viewing with the corresponding eye. In your other hand, gently pick up a loose diamond or gemstone (if jewelry is being examined, hold the piece with your bare hand) with a pair of diamond tweezers. As with a loupe, it’s best to practice handling a loose diamond or gemstone using tweezers as much as possible so that you don’t repeatedly fumble the attempt. Once you feel comfortable handling loose stones with tweezers, it’s on to the next step – viewing the stone through a loupe.


Jeweler holding diamond loupe

Step #2: With your other hand, gently pick up the loose diamond or gemstone with a pair of diamond tweezers. You’re now ready to “loupe” your diamond! Here we are louping a 0.79 ct. Fancy Intense Pink-Purple diamond –


Find a good light source. Daylight, or simulated daylight, is highly recommended. A fluorescent desk lamp is sufficient if you do not have access to daylight. The light source you use to view your diamond, gemstone or jewelry should not be excessively bright or dark. With the diamond or jewelry in one hand and the loupe in the other (dominant hand), bring the lens of the loupe to your eye. At first glance, the item under the loupe will most likely appear blurry through the lens. Bring it into focus by slowly and carefully moving the item – not the loupe ­– around until it clearly appears. This will require a bit of patience especially if you have never or only rarely used a loupe to view diamonds. Generally, the distance required between the item under observation and the loupe is half an inch, although this can certainly vary from person to person. If you find your hands wobbling, sitting down to inspect your diamond or jewelry may be best. To ensure maximum stability of your hands, rest both elbows on a desk or similar hard flat surface.



Jeweler inspecting loose pink diamond under loupe

Final Step: Bring the loose diamond up to the lens of the loupe, leaving about half an inch of space between the two, until the diamond is in focus. Having the diamond in focus may require some effort and patience. If so, make sure you move the diamond around – not the loupe itself.


If you are louping a diamond for clarity, make sure to first wipe its surface with a clean diamond cloth. This will remove all traces of dust and skin oil so that you don’t mistake them for inclusions and blemishes. Look at the diamond through the top and bottom to be sure you have covered all the locations of its inclusions and imperfections. Rotate the diamond continuously with your tweezers, and as you do so, tilt your diamond from side to side, to view it from every angle. When looking at diamond inclusions, a common rookie mistake is to misinterpret the prongs of the tweezers as inclusions – avoid this misstep by rotating the diamond, as well as viewing it from the bottom, to check whether the perceived inclusion is still there. If in doubt, ask an experienced pair of eyes to verify that what you’re seeing is actually present.


Final Recommendations


If you’re just starting out with the diamond louping process, the most important thing you can do for yourself is to practice looking at diamonds, gemstones and jewelry through a loupe. Practice truly makes perfect. Be patient and take your time. Microscopic imperfections and flaws are easy to miss if you rush so spend as much time as you need until you’re confident you’ve seen everything.


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