How to Use a loupe to Inspect Diamonds and Gemstones

Using a loupe while looking at a diamond or a gemstone can be useful even for the beginner. A loupe in the hands of a gemologist is even more useful because of the knowledge acquired through training and experience.

The trained jeweler can tell if a stone is synthetic, natural, a moissanite, glass, or a composite stone. The trained jeweler will also easily be able to spot flaws, cracks, or blemishes.

The beginner will be able to see

  • If the symmetry of the stone balanced. Look at different stones and compare the different shapes of the stones. Also look at the shapes of the facets cut in the stone to see how proportional the cuts are. Is the stone too shallow from top to bottom or too wide from left to right? Stones are like snowflakes. No two stones are alike. After looking at a good well balanced stone and then a bad stone it will become clear the difference. One stone may look short and fat while the other looks proportionally correct. Something else to note is that some stone cutters take pride in their work and do an excellent job while others may not.
  • Chips, scratches, and cracks. Look for chips around the edges of the table where the prongs are secured against the stone. Rotate the stone in the light looking inside the stone, through the stone, and also on the outer surface and edges. imitation glass stones will often have scratches. Zircon stones may have chips.
  • Inclusions, imperfections, flaws, and bubbles. Rotate the stone in direct light while looking through the stone looking for black dots, clouds, white spots, cracks, or any other visual characteristic that is not clear. Also look on the surface for inclusions. If the inclusion is on the table or top of the stone it will be more visible than if the inclusion is in an area where it can be hidden by a prong our under the stone where it will not be seen once set in the piece of jewelry.

The standard loupe to use for inspecting jewelry is a 10x (10 times) triplet loupe black in color. Other color loupes like gold or silver loupes can alter the color of the stone. 10x is also what is required by the United States Federal Trade Commission to grade stones. Hold the loupe with your forefinger and thumb while pressing the hand holding the loupe against your face for stability. Rest the tweezers against the ring finger of the hand that is holding the loupe. Without tweezers the little finger and ring finger of the hand holding the stone can rest on the hand holding the loupe. Either way you hold the stone and loupe we will want to have the hand holding the loupe stable and pressed against the face and the hand holding the stone to be stable and rested on the hand holding the loupe. This will make it easy to rotate without losing focus.

To use tweezers start out by placing the diamond where it is upside down on its table resting on a flat surface. Use the tweezers to grab the girdle of the stone which is the outer edge of the table. First look at the table side then rotate the stone to look at the sides and bottom.

A Few Tips

  1. Always be sure to clear any debris or oil that may be on the surface before you begin to inspect the stone. This can be done with a fine cloth.
  2. Make sure there is adequate lighting to see through the stone. Many jewelry stores have incandescent lighting. Fluorescent lights are used when grading a stone and is proffered. Look at the stone under different lighting if possible.
  3. Hold the stone with tweezers if possible. Be sure to not drop the stone and position yourself so if the stone does fall out of the tweezers that it doesn’t have far to fall or lands on carpet or something soft. Tweezers are best because oil from fingers can look like imperfections.
  4. Look at an unmounted stone when possible. You will be able to see more angles and the stone will have more lighting going through it.
  5. Look at the stone without the loupe to see if any imperfections can be seen. If imperfections can be seen without the loupe then the stone is graded in a lower category and is worth much less.
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