Color-Grading Diamond: the Master Stones
You know that CZ—cubic zirconia—is not a good replacement for diamond in a ring.
How about using CZ to grade the color of a diamond? Once again, CZ is not an acceptable substitute for diamond.
Color grading a white diamond is really about the absence of color. Any hint of color lowers the value of the diamond, and the stronger the color, the lower the gem's worth. The color grading scale established by GIA, and recognized around the world, has letter grades to describe the increasing presence of color.
Master Set of GIA-graded Diamonds
To grade the color of a diamond, GIA recommends comparing the stone in question to a master set of diamonds previously graded by GIA. Diamonds in a master set are carefully chosen to represent letter grades on the GIA color scale.
A typical master set has 5 GIA-graded diamonds. The photo above shows an expanded set of nine diamonds. A key in front labels the grade of each stone in the set. Of course, the fine color distinctions among the stones are not visible in a photograph on your computer screen. Even in person, it takes a gemologist's trained eye to distinguish the very subtle color difference from one grade to the next.
Because a precise color grade is a crucial ingredient in arriving at the valuation for a diamond, most appraisal organizations (NAJA excepted) require a master set of 5 GIA-graded diamonds, and that is what most serious appraisers use.
A set of diamonds is rather expensive, costing several thousand dollars. To save money, many appraisers use a master set of CZ stones instead. GIA, AGS, AGA and ASA do not accept CZ master stones nor will they certify a lab using CZ.
The CZ Problem
Cubic zirconia available these days is lab-made, and the stones can be produced in various colors. To make a set of master stones for grading, CZ stones are made to match the diamond master stones graded by GIA.
You might think that, since CZ stones more or less match the GIA diamond masters, using CZ masters would be OK. The problem is that, while diamond color is stable, CZ color can drift over time from exposure to heat or light.
To remain accurate, CZ masters must be checked against GIA-graded diamond masters from time to time to be sure they are still true to their stated grade. Stones that have faded should be replaced. But typical appraisers using CZ masters do not "update" their master set.
If the colors in a CZ master set have faded, the appraiser will be grading diamonds higher than their true grade. That is, the color grade on the appraisal will be inflated. Many jewelers, and even many jewelry owners, feel a discrepancy of this kind isn't very important because the appraisal is, after all, "only for insurance."
What it means to insurers
An inflated color grade—whether done deliberately, or through inadequate experience, or because of improper grading tools—can matter a great deal at settlement time. For high-quality diamonds, a difference of one color grade can mean thousands of dollars.
But how can an insurer know whether the appraiser used CZ stones (of questionable accuracy) or GIA-certified diamonds for grading?
Ideally, this information should be given on the appraisal—as it is on the insurance industry's appraisal standard, JISO 78/79. The second side of a JISO appraisal provides much specific information, including the appraiser's credentials, purpose of the appraisal, warranty info, grading charts, and the gem lab equipment used for testing and grading stones.
GEM LAB & TESTING
The appraiser certifies that this appraisal was performed in a lab equipped with the gemological instrumentation necessary for a thorough and complete appraisal of the item(s) being appraised. Such instrumentation includes but is not limited to the following equipment: binocular 10x microscope with dark field illuminator, DiamondLite or comparable equipment, dichroscope, fiber optic lighting, filters and lenses, leverage gauge, millimeter gauge, optical measuring device, calipers, ruler, long and short wave ultraviolet lamp, master set of five color-graded master diamonds certified by the GIA Gem Trade Laboratory, master set of colored stones or color communication system, metal testing acids and gold tip needles, penlight, photographic equipment, polariscope with interference figure sphere or lens, refractometer, scale that gives weights in carats, grams, and/or pennyweight to .001, spectroscope, and dual tester measuring thermal and electro-conductivity.
From JISO 78/79 Appraisal Form
The text on JISO 78/79 explicitly states that the gemologist uses a "set of five color-graded master diamonds certified by the GIA Gem Trade Laboratory."
The majority of insurance appraisals carry no such language. Even those multi-page appraisals, that may expound on the appraiser's education, work résumé, and professional affiliations, or that give tutorials on the 4 Cs of diamond, rarely mention the master set used for color grading.
The truth is that most appraisers use CZ stones for color grading. In fact, some gemologists do not write appraisals on JISO 78/79 specifically because they don't use GIA diamond masters and therefore cannot meet that JISO requirement.
What to do? Pick your battles.
The possibility of a grading error because of faded CZ stones is more important for high-quality diamonds than for stones of lesser value, since the financial risk is greater. So our suggestion is, pick your battles.
- When the appraisal you receive describes a diamond of high quality (high grades in both color and clarity), insist on a grading report from a reliable lab such as GIA to verify the quality.
A reputable lab will use GIA diamond masters for color grading. The lab will also have up-to-date equipment for determining other gem qualities, and it will use the latest means for determining whether the stone in question is a mined diamond or is lab-created. Both are "real" diamond, but lab-made diamond has a considerably lower valuation.
If the lab's grades agree with those on the appraisal, all is well. If they disagree, you would do better to trust the word of GIA's diamond lab. - When the jewelry described on the appraisal is of lesser quality (say, H or lower in color, SI2 or lower in clarity), the price differential from one color or clarity grade to the next is not so great. In such a case, you may want to just go with the appraisal description.
FOR AGENTS & UNDERWRITERS
Labs these days can produce diamonds of fine color and clarity, so be sure the appraisal specifies whether the diamond is mined (sometimes called natural) or lab-made (sometimes called synthetic or man-made). Mined diamonds have a much higher valuation than lab-made gems of similar quality. You don't want to replace a lab-made diamond with a mined one.
Occasionally an appraisal will mention the "color master stones." Be aware that "color master set" does not mean diamond masters. If an appraiser were using a GIA master set of diamonds and chose to reference that on the appraisal, the appraiser would say GIA master diamonds.
For all diamonds of high valuation, ask the insured for a report from a reliable lab such as GIA, AGS or GCAL, to verify the gem's qualities. Where there is a conflict between grading opinions, gemologists and insurers regard GIA as the final arbiter.
If you have a lab report number but do not have the report itself, or if you have a report that you want to verify, you can often get a copy online. Here are the links for verifying reports from the major labs:
GIA
AGL
Gübelin
AGS
GCAL
IGI
EGL
FOR ADJUSTERS
GIA is the most highly regarded authority on diamond grading. Other labs may use more flexible grading.
Whenever a lab report was used for insuring the diamond, your replacement diamond should be certified by the same lab. That is, replace a GIA-graded diamond with a GIA-graded diamond of the same qualities; replace AGS with AGS, IGI with IGI, EGL with EGL, etc. You'll find that GIA stones are more expensive, because GIA has more rigid standards, but getting a stone certified by the same lab ensures that the replacement is the same quality as the original.
If documents on file do not specify whether the stone is mined or lab-made, use every means possible to determine this before settling the claim. Mined diamonds have a significantly higher value than lab-made diamonds of similar quality.
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