International Gem Society

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10X Loupe, The Gemologists Best Friend
By Donald Clark CSM

... The simple hand loupe is the most valuable tool of the gemologist. You can learn more with it, and with greater ease, than any other instrument. Add to that the fact that it is your least expensive piece of equipment and it fits easily into a pocket, purse or briefcase and you begin to see why it is called, "the Gemologist Best Friend."
... Loupes come in several varieties. Watch makers prefer the kind that are held by the eye socket. There are loupes that are worn like eyeglasses, or those that clip onto your glasses. Some are illuminated, have built in tweezers and other fancy features. For gem examination, the hand loupe is preferred.
... Ten-power magnification is the most useful for our purposes. Above that the depth of field, the area that is in focus, is so small that they become hard to use. A microscope is the best tool for higher magnification. Lower powered magnification also has its place, but you can't see as much detail. So ten-power has become the standard for hand held gem examination.
... One of the terms used to describe a loupe is "triplet." That means that is has three lenses. This arrangement has no distortion around the edges. Another feature in a high-end loupe is to give the lenses a special coating for "color correction." That means that the colors you see are natural and not distorted by passing the loupe.
... The standard for judging the quality of diamonds is what an expert can see in good lighting, with a 10X, color corrected, triplet loupe. By usage, this has become the standard for professional evaluation of colored stones as well. However, that doesn't mean you need an expensive loupe for study. You can get as much information and enjoyment from a less expensive model.

How to use a hand loupe.

... Using a loupe gracefully takes a bit practice, but soon becomes second nature. When you open a loupe the cover becomes a handle. Slide your index finger through the opening and then rest your hand against your cheek. This is to steady the loupe. Now you only have one hand to move for focusing.
... Before you focus on anything, consider the light around you. If you want to see the surface of the gem, to evaluate the cutting and polishing, you will want the light shining down on the stone. If you are in a room with an overhead light, this is simple. If your best light source is a window, you will need to position yourself so the light is coming over your shoulder. The most important thing is to avoid having your shadow on the stone.
... To see the inclusions in a gem you need the light behind the stone and shining through it. Often you can get to see both the surface and the interior of the gem with a minimum of adjusting. These two conditions are almost always easy to achieve with a little thought. The only limitation is having too little light to see well.
... To focus your loupe, hold your loupe hand firmly against your cheek. Keep both eyes open, (this reduces eye strain,) and hold the gem in front of the loupe. Next, position the gem in front of the loupe. Move it slowly towards and away from the loupe until it comes into focus. Then practice adjusting the focus from the top surface to the far side. On a small gem you can get the entire stone in focus at once. On a larger gem you will have to focus on one area at a time.

Examining the exterior of a gem.

... Begin by studying the surface of the gem. What you are looking for is the quality of lapidary work.
... As you look over the surface, is it smooth and glass like? That is the sign of a perfect polish. You may see pits or scratches. If they are few and not visible without magnification, they will have little effect on the beauty of the gem.
... You will sometimes see stones that have the entire surface covered with small pits. While they aren't visible to the naked eye, they do have an effect on the brilliance of the gem. The reduction of brilliance isn't readily apparent, but takes experience in comparing gems to see.
... At times you may have trouble distinguishing if the marks are on the surface of the gem, or inside of it. To solve this, rotate the gem so the light reflects off the facets. When a facet acts as a mirror, inclusions beneath it disappear, but scratches on the surface are still visible.
... Is the girdle polished? If not, it shows the gem was cut in a hurry. A custom gem cutter would finish this off. Diamonds are an exception to this though. They are cut different than colored stones because of their extreme hardness. A rounded and unpolished girdle is common.
... To further evaluate the quality of cutting, look at the "facet meets". On a well-cut gem, they form sharp corners and all the facets in a row will be the same size and shape. It is common to see facets that vary in size and corners that don't meet or overlap. If the differences are small, they won't have a significant effect on the beauty of the gem. As the problems increase, the brilliance of the gem begins to suffer.
... How sharp are the facet edges? This is an interesting clue to look for. Diamonds, with their incredible hardness, have the sharpest edges. That is a clue to their identity. Your harder colored stones, CZ's, rubies and sapphires come in a close second. Softer gems, those below nine in hardness, will usually have slightly rounded facet edges. Once in a while you will come across a custom cut gem with exceptionally sharp edges in a material that is only 7 or 8 in hardness. Even though you may not be able to appreciate all the subtle decisions that went into cutting a gem like this, you can spot the quality of workmanship by the polish, meets and facet edges.
... Turn the gem upside down and look at the culet. It may well be chipped. This is called "paper damage" and refers to what happens when gems are carried together in paper wrappers. Again, if it isn't visible without magnification, it won't have a significant effect on the beauty of the gem.
... I think that you are beginning to see how the quality of lapidary work affects a gem. A minor imperfection or two is acceptable, but several examples of sloppy workmanship diminish the beauty of the gem. This is true even if they aren't individually visible to the naked eye. If you are a beginner, you may never have had the chance to appreciate this before.
... When you examine a cabochon, you begin by judging the polish, just as you would with a faceted gem. Look for any scratches or pitting that will reduce the amount of light reflected from the surface.
... The next thing to look for is how even the contour is. A cabochon should have an even curvature to its surface. Look at the cab from both ends and both sides. The shape, (the curvature,) should be a mirror image from side to side. No area should be thicker than its opposite and there should be no bulging.
... The second way to judge the shape is to hold the gem so light reflects off its surface. Then move the gem so the light travels across the top. If the surface is properly cut, you will see the band of reflected light glide evenly over its surface. The band of light will begin to snake if there are any irregularities.
... The very top of the gem is where you are most likely to see this. Often a small area will be somewhat flattened. This is hard to see when viewing from the side, but quite obvious as light passes over it. The fact that light doesn't flow smoothly over this area is why it is considered to be second-rate workmanship. However, if you look closely, that area probably doesn't have as good a polish either.

What is inside?

... One of the most interesting and useful elements of gemology is the study of inclusions. As you begin examining gems, you will encounter quite a variety of internal paraphernalia. The definition of an inclusion is anything that will affect the flow of light. While this sounds negative, you will find that some inclusions are beautiful. Others are nothing short of incredible, as you learn what they are and how they got to be inside the gem.
... One of the easiest categories of inclusions to identify are fractures. Emeralds almost always have internal fractures, while they are uncommon in most gems. Tiny, internal fractures that don't reach the surface will have minimal effect on the durability of the gem. The fact that they have gone through the cutting process without damage attests to that. Larger fractures, or those close to a thin edge, are significant.
... If a fracture reaches the surface of the gem, it has the ability to absorb liquids. Over time this can absorb dirt and skin oils and lose some of its brilliance.
... In emeralds, this feature is used to absorb oil or other substances with the same RI as the gem. This makes them much less visible. To see them, you need to look very closely and get the light on them from just the right angle. If you see a multicolored radiance, like an oil slick, you have spotted a filled fracture.
... Sometimes a fracture will stand out, interrupting the flow of light. Other times the fracture is pressed so tightly together that light will flow right through the fracture. This type will show a bright, multicolored flash when light strikes it from the correct angle.
... Most fractures have at least a slight bit of curvature in them. Look carefully to see this. If you encounter one that is perfectly straight, that is most likely a cleavage fracture. Gems have cleavage planes that are much like the grain of wood. Along the cleavage plane the gem splits easily. Finding a cleavage fracture in a gem is a sign of significant weakness.
... The other most common type of inclusion are other minerals. These can be small bits of debris or miniature, whole crystals. Afghani peridot sometimes has clusters of tourmaline that look like flies. Spinel can be included with tiny spinel crystals arranged in a plane. These are often spectacular!
... Some mineral inclusions are opaque. Their size and number have to do with how much they will interfere with the passage of light. Black, "carbon" spots in diamonds are a common example of this.
... Other inclusions are transparent. How visible they are depends on their RI. If they are significantly different than the surrounding crystal, they will jump right out at you. In other cases, like spinel in spinel, they are nearly invisible. To see them you need to have a dark background behind the gem and light coming in from the sides.
... "Silk" is found in several gems but it is particularly common in corundum, spinel and garnet. This is a pattern of very slender, thread like, crystals. When they are fine enough and all arranged in the same direction, you get the impression that you are looking at the gem through a fine layer of silk, or seeing it inside the gem. The greater saturation of the silk, the more brilliance of the gem will suffer.
... You are also going to see a number of voids in your gems. Some are bubbles of gas that got trapped inside the crystal as it formed. Besides gas, they may contain a liquid or a crystal. Finding two or three of these in one cavity is a rare treat for the gemologist. It can also be a significant clue as to the identity of the gem.
... You may be surprised to see what looks like a fingerprint in a gem. That is called a "healing fracture." At some point in the crystal's history, it got broken. Then the conditions for growth became present and it grew back together, or healed.

... Fractures, minerals and voids are the primary type of inclusions you are going to see. However, there are a few specific ones that are of interest. Peridot is known for its "lily pad inclusions." They are a small black spot surrounded by a curved fracture that looks just like a lily pad. This is common and easy to spot.
... You may see something similar in a ruby or sapphire. They will sometimes have an opaque inclusion with a fracture around it. They won't be as beautiful and symmetrical as in a peridot. This is an indication that the gem has been heat-treated. When it got hot enough the inclusion burst, creating the fracture around it.
... Dematoid garnets are identified by their distinctive "horsetail" inclusions. The name is descriptive and if you ever see one there will be no doubt what you are looking at.

Coloring

... The color in gems may not be evenly distributed. This is most evident in stones like Ametrine and watermelon tourmaline, which are cut to show off the separate colors. In most gems though, you need to look carefully to see it.
... Amethyst is known for its "zoning". It may have areas of dark purple surrounded by lighter purple or even colorless quartz. With careful cutting, orienting the color in the culet, the gem will be evenly colored face up. This brings the gem to its highest beauty and eye appeal. If you can see the zoning face up, or with just slight tipping, it reduces the value of the gem.
... This is also common in sapphire. The same principle applies, if you can't see the zoning face up; it has no effect on the value of the gem.
... The zones of color in an amethyst will be random, while the zoning of a sapphire is in straight bands. They are present even if they aren't distinct enough to be seen with the naked eye. The best way to see them is to view the gem from the bottom with light coming in from behind it.
... You have to be looking directly on to the plane of color to distinguish the banding. Due to the cutting, the banding will only be visible in one facet at a time. It takes a bit of practice to see this, but it is worth learning.
... When you see the banding, check to see if it is straight or curved. If it there is any curvature, it will be subtle so you have to look carefully to perceive it. However, this is very significant. If the striae, the banding, are curved that means it is a flame fusion synthetic. Straight banding can be natural or synthetic.
... So you see how much information you can get from a loupe. If you are a beginner, this will probably bring up dozens of new questions and they will direct you to your next level of study.

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