How Colored Stones are Graded

Color is the dominant feature of a colored stone, and thus is weighted in the grading process. Color grading is subjective. The color is described in terms of Hue, tone, and saturation.

Generally speaking, highest values go to stones with pure hues and strong rich colors. With high value gems, subtle variations make a significant difference in price. For example, a slightly orangish ruby will not be worth nearly as much as one that is pure red. Most people cannot see the difference, but to the expert grader it is significant.

On moderate priced gems, color has less affect on value. For example, tourmaline comes in every possible color. Unless it is an exceptionally pure green, red or pink, they are all about the same value. It is the other factors of size, clarity and cutting that determine the gem’s value.

Diamonds are graded on how close they are to being colorless. There are three grades of “colorless” that only vary by subtle differences in transparency. Then there are four grades of “white.” These are gems that will appear colorless when set in jewelry. It takes an expert in a laboratory setting to distinguish between these grades, but each represents a change in value.

The color that is best for you is a personal matter. Strong, bold colors correspond with strong personalities; others prefer something softer and brighter. The color of your complexion and the color of the clothing you prefer also have a significant effect on your gem choice.

To find what colors are best for you, look at a lot of gems. You will find that subtle variations in color can have a significant affect on both how they look on you and your emotional reaction to them.

If you are a connoisseur of fine gems, the higher grades are significant. On the other hand, the average consumer will find just as much beauty in the more modestly priced stones. Remember, quality does not mean better, it means rarer.

Transparent colored stones are divided into three type classifications depending on crystal growth characteristics, and then graded within their type class, for clarity.

The G.I.A. grading system for colored stones lists clarity type classifications as Type I, Type II, and Type III. The classifications are defined as follows:

• Type I- These are gems that grow extremely clean in nature and usually have no eye-visible inclusions. An example is Aquamarine.
• Type II- These are gems that typically grow with some minor inclusions in nature and the inclusions may be eye-visible. An example is ruby.
• Type III- These are gems that typically grow with many inclusions in nature and the inclusions are usually eye-visible. An example is emerald.

Colored stones are also graded for cut. Cut grading includes observance and qualification of brilliance, proportions, bulge, overall symmetry, and finish.
The cut of a gemstone, the workmanship that went into fashioning it, is one of the most important factors in its appearance. It is also one of the most difficult factors for the non-professional to judge because of the number of variations involved.

The first thing to do is to look at the shape of the stone. Some gems are cut “freeform” but most are intended to be a regular shape. If so, 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, it is up to you to determine how much it will affect your appreciation of the stone.

Good Cut vs. Poor Cut Gemstone

When considering a gem, insist on inspecting it with magnification. Look at areas where light is being reflected from the surface. They should be smooth and mirror like. If you see pitting, scratches, or dull areas, the gem is not well polished. It may look good in the store, but someday you will compare it with a well polished gem and be disappointed with your purchase.

If it is a faceted gem, look at the facets junctions also. On a well cut stone, they will be crisp and come together in a single point. You may see facets that are slightly rounded and not quite meeting where they should. Just how far off they are will affect the brilliance of the gem.

The other factors in a faceted gem are too complex for the lay-person. However, you can get a good idea of the cutting quality simply by comparing it with other gems. When you do this, make sure you are comparing similar stones. An amethyst will never have the brilliance of a topaz and dark stones will not be as bright as light colored ones.

When comparing like stones, what you want to look for is the overall light return, the brilliance and sparkle of the gem. It is entirely possible to look at two gems with the same size and coloring, but one having much more brilliance and sparkle than the other. This is the result of cutting.

One thing to pay special attention to is “windowing.” That is where light passes straight through the center, rather than being reflected back. It is easy to spot; 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.

This is another example of something that might look good in the store, but someday you will compare it with a well cut gem and be disappointed with your purchase.

Cabochons are easier to judge. Begin by checking the polish under magnification. Then hold the stone a short distance from your head and rotate it slowly. Notice how the light passes across the surface. On a well cut gem, it will flow smoothly from one side to the other. If it is poorly shaped the light will not flow smoothly, but snake across the surface. Surface irregularities and poorly polished areas will also show up this way.