Last updated on June 15, 2021
A jeweller’s loupe can tell you a lot about a diamond you are going to buy. It will help you examine any defects that may not be visible with the naked eye and avoid potential disappointment after the purchase. In this guide, you will find out how to inspect a diamond with a loupe and make a good buying decision.
What Is a Jeweller’s Loupe?
A loupe is a small magnifying glass used by jewellers to inspect gemstones and jewellery. The tool ranges from 10x to 30x magnification and usually folds in on itself for easy carrying.
The loupes jewellers usually use have 10 times magnification because diamond grading is done under 10x. Besides, higher power lenses have a reduced focal length (the distance between the object and the loupe to get the best focus) and a very narrow field of view (the size of the area visible through the lens), making it very difficult to inspect a diamond under such conditions.
There are different types of jeweller’s loupes that are designed with a different number of lenses. The more common ones are doublets and triplets; however, there are also loupes made with a single lens with restricted magnification allowed. A loupe featuring three optical elements/lenses is the best option as more lenses allow better inspection. The most popular lens diameters are 18mm and 21mm. Larger lenses give a better image quality as more light can enter through them.
How to Inspect a Diamond With a Loupe
The proper way to use a jeweller’s loupe is to hold it close to your eye with your hand making contact with your face. You can hold the diamond or the gemstone you are going to inspect with the other hand. However, you should make sure your hands are clean before touching diamonds with your bare hands. The professional way to handle gemstones is using tweezers, but this requires some practice.
It is recommended to put your elbows on a table to steady yourself and to be able to move the diamond in and out to change the distance between the gem and the loupe to get the best focus.
At first, the image you see through the magnifying glass looks blurry and out of focus. To adjust the focusing, you will want to move the diamond inwards and outwards until you get a sharp image. Remember to keep your louping hand still all the time. Once the image is in focus, check the diamond’s face-up appearance, then inspect the gem from different angles. Finally, verify whatever you see against the grading report. If you see flaws that cannot be identified, ask your jeweller for clarification.
What to Look for When Inspecting a Diamond
Diamond inclusions are natural birthmarks that develop when a stone is formed in the earth’s mantle layer at a depth of 80 – 120 miles. Some types of inclusions can be potentially harmful to diamond structure, while others can be annoying but harmless. For example, black dots, which are simply areas where carbon has not crystallized, apart from being an optical flaw, do not present any real danger to the structure of diamonds. However, dark crystals can block the light entering the stone, resulting in reduced fire, brilliance and scintillation.
Inclusions like cracks and feathers may be dangerous. If they are big enough, they can weaken the stone’s internal structure. With this in mind, you will want to avoid diamonds with long feathers, especially the ones with lines that reach the surface of the stone. Such inclusions make the stone even more prone to damage, meaning the diamond will most likely crack if hit hard enough.
Always check the surface of the diamond for chips and cavities. If the stone has chips it is more vulnerable to stress, and in case of a strong hit, it may just split along the cracks.
Make sure to check the certificate of the stone. It should contain a diagram of the diamond showing all the visible inclusions. This will help to check if the flaws showed on it match the ones you see with a loupe. This is also a good way to identify if the certificate describes the same diamond you have.
Inspect the diamond for signs of clarity enhancement, such as laser drilling or fracture filling.
Laser drilling is a technique used to remove inclusions such as black spots or foreign crystals embedded within a diamond’s crystalline structure. Such diamonds have tiny channels inside them visible under 10x magnification. These channels used to have an inclusion inside, which was dissolved with heat or acid. You will be able to see small hollows that have remained after the flaw was removed. Sometimes these hollows are filled with a glass-like substance in a process called fracture filling. The filled substance reflects the light differently from the rest of the diamond, and it is easy to spot with a loupe.
The drilled channels in a clarity-enhanced diamond are not critical unless they are numerous. In this case, they may weaken the internal structure of the stone, especially if the removed flaws took up a lot of space. Fracture-filled diamonds are more problematic. The filling can melt and crack if the piece of the jewellery is repaired using heat.
It is important to mention that jewellers are required by law to fully disclose if the diamond has been clarity enhanced regardless of the improvement type. So do not hesitate to ask if the diamond has been treated because many jewellers are not quick to disclose that info before making the sale.