Gem Grading

The “Four Cs” of gem grading stand for colour, clarity, cut, and carat (weight). Gemologists grade gemstones based on these properties. 

Even though we may use the term “quality” when describing the properties of gems, that doesn’t necessarily mean that one gem is better than another. Ultimately, you’ll purchase the gem that’s best for you personally. What’s best for you may not necessarily be the “top” or rarest grade of the gem.


Feature Rarity and Gem Grading

Gemstone deposits will yield pieces with a wide variety of qualities. For instance, let’s say somaeone just mined 100 pounds of amethyst and brought them to a gemologist for grading. One of the first things the grader will notice is the size variation. The smaller stones will settle at the bottom of the pile. This leaves the larger stones on top, demanding the most attention. Since there are fewer large stones, they’ll receive a higher grade in the size category than the smaller ones.
For amethysts, a 100-carat stone is rarer than a one-carat stone. Therefore, that feature will add to an amethyst’s value. However, simply being larger doesn’t make it better. A small person couldn’t wear such a huge stone gracefully. It wouldn’t be the best gem choice for someone with a slight build.
The same principle applies to the other grading factors, too. As the grader continues going through the amethysts, only a few gems of the absolute deepest and richest colouring emerge. These will command special attention and pricing due to their rarity. Once again, however, consider what you want as a consumer. Bold coloured gems aren’t the best matches for every complexion or personality. Softer pastels may suit some people much better.
Gem grades reflect the rarity of the feature. They don’t measure beauty. With only one exception (cut), gem grades won’t indicate which gem better suits your needs.  When choosing a gem, use gem grades to help you look for a stone that will give you the most enjoyment.
Gemologists describe gem colour by referring to three properties: hue, tone, and saturation.
When most people describe colours, they most likely mean hue. The basic hues are red, orange, yellow, green, blue, violet, and purple. Black, white, and brown refer to tones and saturation, not hues.  
A gem’s tone refers to a gem’s relative lightness or darkness. Black and white are tones, from darkest to lightest.  A gem’s saturation refers to the intensity of its hue. Colours can be strong or soft. Pink is desaturated red. Warm colours, like red and orange, become shades of brown as their saturation decreases.
Generally speaking, highest values go to stones with pure hues and strong, rich colours.
With high-value gems, subtle variations make a significant difference in price. For example, a slightly orangish ruby won’t be worth nearly as much as a pure red. Most people can’t see the difference. To an expert grader, however, it makes a significant difference.


What colour Gems are Right for You?

The colour that suits you best is a personal matter. Your personality, complexion, and even the clothes you want to coordinate with a gem will influence your choice. Look at a lot of gems. You’ll find that subtle colour variations can significantly affect how they look on you as well as your emotional reaction.
For connoisseurs of fine-quality gems, higher grades are important. On the other hand, average consumers can find just as much beauty in modestly priced stones. Remember, quality doesn’t mean better, it means rarer.


Gemstones contain a wide variety of inclusions. In faceted gems, inclusions are defined as anything that will interfere with the free passage of light. These can include little bits of minerals, hollow areas, and fractures. Clarity gem grading addresses the visual and structural impact of these things.
Gemologists simply grade most coloured stones either “eye clean” (inclusions invisible to the naked eye), slightly, moderately, or heavily included. Eye visible inclusions always lower a gem’s value, but the change isn’t applied equally. coloured gems are also grouped into three clarity types:

Type I, usually eye clean
Type II, usually included
Type III, almost always included.

Emeralds are Special Cases

Emeralds fall into the Type III category. However, you can’t compare their clarity with any other gems. If you want an emerald without any eye visible inclusions, you’re limited to small stones. Otherwise, if you want a larger emerald, you must accept the inclusions and find value in the colour.
If this compromise doesn’t appeal to you, consider other green stones, like tourmaline and diopside. Their colour can equal that of fine emeralds, without the inclusions, and at a much lower price. Now, you must choose between having the name “emerald” or a premium green colour.


Balancing Clarity and Price

Although eye visible inclusions always affect value, you can sometimes use this to your advantage. I remember one young woman showing off her diamond engagement ring. She had me look real close to see three tiny black dots. By accepting those small inclusions, invisible from further away than six inches, her fiancé could afford a much larger diamond.  You can also find just slightly visible inclusions in coloured stones. Even some moderately included gems, like a dark garnet, will look fine when viewed from a normal jewellery distance. You’ll have to decide if this will interfere with the joy you get from the stone.

Inclusions and Structural Integrity

While beauty lies in the eye of the beholder, fractures and veils can lie deeper in the gem. Pay special attention to these inclusions. They represent a weakness in the gem, which may be prone to breakage. Earrings, pendants, and brooches don’t receive much abuse. Ring stones, however, take a constant barrage of bumps and bangs. If you’re looking for a ring stone, avoid a weak gem.
Non-professionals will find identifying these inclusions difficult, let alone determining their impact on structural integrity. The old saying, “If you don’t know your gems, know your gemologist,” applies here.


A gemstone’s cut, the workmanship that went into fashioning it, is one of the most important factors in gem grading. It has a tremendous effect on a gem’s appearance. The cut is also one of the most difficult qualities for the non-professional to judge, due to the variations involved. Nevertheless, consumers can conduct some basic examinations.


First, look at the shape of the stone. Of course, some gem cutters carve gems into beautiful “freeform” shapes. Most gems, however, are intended to have regular shapes. If this is what you’re looking for, look at the symmetry. Does it bulge here or there, or is it symmetrical in all directions? Look at the stone from the side and the ends. Again, it should be symmetrical in all directions. If not, you must decide how much that will affect your appreciation of the stone.


Insist on inspecting any gem you’re considering buying under magnification. Look at the surface areas that reflect light. They should be smooth and mirror-like. Pitting, scratches, or dull areas indicate a poor polish. Such a gem may look good in the store, but someday you’ll compare it with a well-polished gem. You’ll be disappointed with your purchase.
If you’re examining a faceted gem, look at the facet junctions, too. On a well-cut stone, they’ll be crisp and come together at a single point. You may see slightly rounded facets not quite meeting where they should. Just how far off will affect the gem’s brilliance.

Compare Similar Stones

While other cut factors may be too complex for non-professionals, you can get a good idea of a gem’s cutting quality simply by comparing it with other gems. When you do this, make sure to compare similar stones. For example, an amethyst will never have the brilliance of a topaz. Dark stones don’t have the brightness of light coloured ones, etc.
When comparing like stones, judge the overall light return. Let’s say you examine two like gems of the same size and colour. If you find one has much more brilliance and sparkle, you’re seeing the impact of cutting.


Pay particular attention to windowing, a condition where light passes straight through the gem’s center rather than reflecting back. You can spot this easily. The center will be much lighter than the outside of the gem and have no flashes of light. Some windows are small. Others are quite large and hideous.Like a poorly polished gem, a gem with a large window might look good in the store. Eventually, however, you’ll notice the difference between a well-cut stone and what you bought.


Choosing Large or Small Gems

Choosing the right gem size is a personal matter. Bold personalities might prefer large gemstones. Someone with delicate sensibilities might prefer smaller gems. Most people will likely fall between these extremes.
For tighter budgets, smaller stones have a significant advantage. Not only do they cost less per weight, the “amount of gem” you see is disproportionate to size. This is because gem volume goes up faster than outside dimensions. For example, a ½-carat, round diamond measures 5 mm in diameter. A ¾-carat diamond measures 6 mm. A full carat diamond measures 6.5 mm.
To a casual observer, the ½ and ¾ carat stones seem about the same size. The ¾ and full carat stones also look about the same size. However, their price differences can be considerable.


Jewelers often cluster small gems to give the illusion of more gemstone.  Seven 1.6 mm diamonds, set close together, will take up as much space as a whole carat diamond. If set on white gold, distinguishing the separate stones proves difficult. Hence, these settings are often called “illusion settings.” While these seven stones approach the visual appeal of a one-carat diamond, they only weigh 0.14 carats. Considering that the price per carat for small diamonds is also much lower, you’ll see a significant cost difference. A cluster ring’s price could range in the hundreds of dollars, rather than the thousands.
You’ll find coloured gems often clustered for the same reason. You’ll get more “visible gem” for less money. If your budget can’t accommodate your first gem choice, consider a setting with several smaller gems. You might just find the look and emotional appeal you wanted at a price you can afford.



Now you know the factors that go into gem grading. Remember that rarer features don’t necessarily mean the stone is “better quality.” Stones smaller or lighter than the top grades may be just right for you.
However, keep in mind that clarity can have an impact on a gem’s durability and jewellery use. Also, cutting can greatly affect a gem’s appearance, so examine cut gems carefully. Always choose the best cut you can afford. (No personality will find a poorly cut stone appealing).
Nature doesn’t always provide perfect gems, nor do lapidaries always produce perfect work.  Be ready to make compromises. You may not be able to afford your first choice of gems.  When shopping for a gem, find what suits your personality best, within your budget.
Finally, the most import factor to consider when gem buying is the joy you’ll get from your gem. 

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