Colored Stone Certificates
are colored stones graded and valued?
What about certificates for colored stones?
Rubies, sapphires, emeralds and other colored stones are a much more complicated world than diamonds. They are more difficult to judge and classify. For diamonds, the most important criterion for value is cut. For colored gems, it is color.
Grading colorless diamonds is fairly straightforward the less color the better. An appraiser can compare any given diamond with a standard set of color grading stones. Based on these grading stones, he assigns a GIA letter grade from D to Z, giving a very precise designation of diamond color.
With other stones, the color differences are much more variable and often quite subtle. Before the 20th century there was no generally accepted system for describing colors. Then Albert H. Munsell, an American painter and art instructor, identified three basic qualities of color hue, tone, and saturation. The GIA adopted Munsell's principles to create gemstone color grading standards.
The GIA specifies 31 gemstone hues. They include terms such as blue, slightly greenish blue, very slightly greenish blue, bluish green, and so forth. The GIA has prepared a color chart showing the hues and their designations.
Tone refers to the lightness or darkness of a color. The GIA has determined 9 levels of tone, ranging from very very light to very very dark.
This is the degree to which a color departs from a neutral (gray) sensation. Saturation can be thought of as the relative purity of a hue. The GIA specifies 9 terms, such as brownish, grayish, moderately strong, and vivid.
The precision of these designations for hue, tone, and saturation (see charts) is important because color accounts for 50% of a colored gem's value.
Colored Stone Certificates
There are several certificates for colored stones. Unfortunately, none of them is up to the quality of diamond certificates (see March & April issues), and the overall value of the reports on colored stones is questionable.
GIA Identification Report
The Gemological Institute of America's report gives shape, measurements, and weight. It mentions whether the stone is natural or synthetic and whether the color is natural. It may also indicate whether the gem has been subjected to treatments. It does not mention clarity. As to color, it gives only hue. It does not give tone and saturation, so the grading for color 50% of the gem's value is worthless!
AGTA Identification Report
The American Gem Trade Association gives shape, measurements, weight and determination as to whether the stone is natural or synthetic. It includes a photo. In our example, the report also mentions that the examined stone was loose (determinations are more likely to be accurate when a stone is examined loose rather than in a setting). Certificates will vary somewhat depending on the stone type (i.e., ruby v. sapphire).
In reporting that a stone was not heat-enhanced, the report adds the comment that it is rare for a ruby/sapphire to not be enhanced by heat. This lack of heat treatment adds value to the stone. AGTA also gives the geographical origin of the ruby, which in some cases can affect value (for example, Burma rubies and Kashmir sapphires have high values). A chart at the bottom of the report shows the tests carried out in the examination of this gem.
However, as to color, AGTA gives the ruby's hue only as red, the sapphire's hue only as blue. These are vague (especially since all rubies are by definition red). The report does not use one of the specific hues from the GIA scale, does not give tone or saturation at all, and does not mention clarity. Therefore, the color grading is worthless!
EGC Gemological Report
The European Gemological Center's report gives shape, weight and measurements, tells us that the stone is natural and there is no evidence of color or clarity enhancement. It gives evaluations for finish, brilliancy and proportions, and includes some cutting information. A photo of the gem is included.
The report includes gemological properties, but these are properties of the gem material in general and not relevant to the grading (or valuation) of this gem. EGC gives a clarity grade based on its own system (not the widely accepted GIA system). No chart is given to show what this grade means, so it is useless. The hue is given only as green. Again there is no indication of tone or saturation, so the color grading is worthless!
AGL Colored Stone Certificate
American Gemological Laboratories' certificate gives shape, weight, measurements, and some cut information, tells whether or not the stone is natural, and gives the country of origin. It grades proportions and gives information on brilliancy and finish.
The certificate includes a labeled diagram of a cut stone. This is not a Sarin report that is, it is not an illustration produced by the machine that measures a stone and calculates its exact proportions. Instead, this is just an illustration showing names for parts of the stone and is not relevant to identifying this stone. The color information and clarity grade follow a system unique to AGL, so it is unreadable to anyone else.
This is unfortunate, as AGL's certificate is by far the best of the certificates available in the USA. Should AGL decide to state the color and clarity grading in GIA nomenclature and include a Sarin report/diagram (both quite easily done), this would be a very good report, worth recommending to insurers.
Unlike diamonds, which are valued primarily on cut proportions, colored stones derive half their value from their color described in terms of hue, saturation and tone. Colors of stones can vary widely. Sapphires, for example, can be not only blue but even variations of pink, orange, purple and green.
Since none of the certificates carries sufficient color information, it is crucial to have an appraisal that does. Look for an appraiser with at least three years experience, who is a Graduate Gemologist and knowledgeable about colored stones. Be certain that all color elements (hue, tone and saturation) are stated. Ideally, have an appraisal on the ACORD 78/79 form.
Colored stones from certain countries have particularly high values. If you are insuring a high-priced stone, have a certificate stating the gem's country of origin. It should also state any treatments (or lack thereof).
Remember that, although GIA's diamond certificate is good (as discussed in the March issue), its colored stone report is not.
While there are fewer claims on colored stone than on diamonds, colored stones usually have much higher markups and generally have inflated valuations. Most buyers are totally unfamiliar with colored stones, and the pricing abuses are great. For example, consider topaz, sapphire or amethyst. How many buyers (or insurers) know that the typical one-carat stone has a replacement cost of about $24.00 for topaz, $174.00 for sapphire or $3.00 for amethyst? Surprised?
Most natural stones are treated, or "enhanced," to make them look more appealing. However, value is based on the real condition of the stone, not its look to the naked eye.
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