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 Click here to download the sample report (PDF, 967Kb).

 

How to Determine the Quality of a Colored Gemstone

In 1977, Cap Beesley of American Gemological Laboratories (AGL) became the first laboratory in the world to evaluate and classify colored stones in a linear, comparative manner. In 2009, new AGL President, Chris Smith, modified the grading system with the introduction of a new grading report, The Prestige Gemstone Report. Both have enjoyed a position of leadership in gemstone documentation and have extensive experience in consumer protection programs.

Some every important changes have been made to the document. The grading system which they devised is comprehensive and requires some study to realize a workable understanding of the process. However, once you grasp the basic principles, you will wonder how anyone could buy a gemstone without using this kind of vocabulary. The following "walk through" of a 3.04 Burma sapphire grading report will help you understand the various components of the Prestige Gemstone Report.

Ideal Parameters

• Carat Weight: 1 carat or larger
• Color: Good (6) or better
• Tone: Ideal tone for ruby, sapphire and emerald ranges from medium to dark (65-85). Ideal tone for other gem types varies from light to medium (20-65).
• Clarity: Moderately Included Two (MI2) or better
• Average Brilliancy: 50% or more
• Cutting/Finish: Good (6) or better

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LEFT

Imaging

The upper left depicts a high resolution color digital image of the stone. This image assists in verifying the gemstone matches the grading report. Please note the image is for representational purposes and may not be the exact actual color or size.

Accu-Vu Imaging

The Accu-Vu is the side view facet arrangement and relevant measurements of the actual stone. AGL uses a Sarin device to obtain a three-dimensional recreation of the actual stone. It also includes key measurements and proportions.

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CENTER

Document Number

The upper left shows the document number. The lab assigns individual, consecutive numbers for each grading report issued.

Identification

In this sample, the AGL has determined the stone is a natural sapphire.

Validation Date

This is the date the gemstone report was completed.

Mineral Type / Variety

This describes the mineral type and variety of the gemstone. In the sample, the gemstone is a natural corundum sapphire.

Carat Weight

Colored stones are weighed with an extremely accurate scale. In the sample, the sapphire weighs 3.04 carats.

Measurements

The measurement of the gemstone in millimeters.

Color Description

A verbal description of the main color of the gemstone.

Shape and Cutting Style

The stone is an oval mixed cut in this sample.

Origin / Provenance

This is where you will find the country of origin of the material. In the sample, the gem is Burma (Myanmar) sapphire. Next to this information is a world map with the country of origin highlighted.

Comments

Here is the full laboratory comment regarding the country of origin.

Enhancement

This section allows for standard and additional enhancement information. The document allows for the type of treatment and the degree of treatment. If not treated, this section should say none. The graph on the bottom left shows the degree of clarity enhancement and its relative rarity. Finally, the gemstone report has a graph showing the stability index of a treatment. This is vital information for consumers attempting to make an informed decision. All AGL declarations meet or exceed State and Federal Trade Commission (FTC) rules and requirements. The sample shows no treatment and no clarity enhancement. Of course, these are the preferred comments.

Comments

Here is the full laboratory comment regarding treatments.

Degree of Clarity Enhancement and Relative Rarity

AGL indicates the extent of enhancement using its ten category classification system.

 

Enhancement Stability Index

This section defines the stability of enhancements under normal wear and tear for the consumer.

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UPPER RIGHT

Color Grade

The color grade is simply based upon the purity of primary color. For example, the greener the emerald, the redder the ruby, or the bluer the sapphire, the lower the numerical grade on an AGL scale. The reason the 3.04 sapphire is a 3.5 in this sample is the fact the stone has 65% blue as its primary color. It is that simple. The less primary color, the higher the numerical color grade. For example, a 60% primary color would probably be graded a 4 color.

The color scan will generally break down into three perceived colors that total 100%. In the sample, the sapphire is 65% blue, 20% violet and 15% green. As a general rule, you will only see the first two colors or the stone will appear violetish blue. With the AGL Prestige Report, we are seeing changes compared to the older AGL colored grading system. Top grades are being pushed upwards. For example, in the old system, a 70% primary color or 3.5 color would probably be the best color grade you would receive. Also, in the past grading system, the top of the line 1.00 and 2.00 color grades were impossible to obtain and these grades were a theoretical standard. The new AGL grading system now allows for for 1.00 and 2.00 color grades.

Tone / Tone Scale (AGL)

In the sample above the sapphire's tone is 75-80, or technically 77.5. Basically, tone describes the lightness or darkness of a gemstone. Color considered alone without taking into account the tone will lead to errors in interpretation. If a stone is too light in tone, the color will not be rich enough. Conversely, if a stone is too dark, it will sacrifice transparency and brilliancy.

Clarity / Clarity Scale (AGL)

Clarity is defined as the degree to which the stone is free of inclusions under 2.5x magnification. In the sample the clarity is LI2-MI1. Here is a good rule of thumb to remember: You will probably not see inclusions in a Lightly Included (LI) gem, you may see some inclusions in a Moderately Included (MI) gem, and you will probably see inclusions in a Highly Included (HI) gem. Excessively Included (E) gems have durability problems and should be avoided.

Cutting/Finish / Cutting/Finish Scale (AGL)

The cutting of a gemstone numerically describes the proportions and geometry of a gem. The finish grade refers to the polish of a gem. In the sample the cutting grade is Good (5) and the finish is Very Good to Good (4-5). Unlike diamonds which are cut according to strict mathematical parameters, most colored gemstones are cut for weight retention.

Depth

The depth of the gemstone.

Average Brilliancy

Brilliancy is the amount of flash the gem returns to your eyes. Most diamonds are 100% brilliant. Brilliancy in the sample is 70%. An average brilliancy of 50% means half of the stone returns flash.

Total Quality Integration Rating

This comment integrates a summary of the visual impact of the gem into a easy-to-use and understand verbal description.

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• For more information on the older AGL Colored Grading Report, click here.

• For more information, visit AGL's web site.