May 24

Jewelry and Gems The Buying Guide – Diamond Grading Report (1)

Today, few fine diamonds over one carat are sold without a diamond grading report, or certificate, as they are also called, from a respected laboratory. Reports issued by the GIA/Gem trade laboratory are most widely used in the United States and many countries around world.
A grading report does more than clarify the stone’s genuineness, it fully describes the stone and evaluate each of the critical factors affecting quality, beauty, and value. Grading reports can be very useful for a variety of reasons. The information they contain can provide verification of the “facts” as represented by the seller and enable one to make a safer decision when purchasing a diamond. Another, important function of reports is to verify the identity of a specific diamond at some future time, if, for example, it has been out of one’s possession for any reason. For insurance purposes, the information provided on the report will help ensure replacement of a lost or stolen diamond with one that is truly “compatible quality.”

Reports are not necessary for every diamond, and many beautiful diamonds used in jewelry are sold without them. But when considering the purchase of a very fine diamond weighting one carat or more, we strongly recommend that the diamond be accompanied by a report, even if it means having a diamond removed from its setting (no reputable lab will issue a report on a mounted diamond), and then reset. If you are considering a diamond that lacks a report, it is easy for your jeweler to obtain one. Or, now that GIA is issuing diamond grading reports to the public, you may submit a diamond at GIA yourself.

Do not rely on the report alone

The availability and widespread use of diamond grading reports can, when properly understood, enable even those without professional skills to make valid comparisons between several stones, and thus make more informed buying decisions. Reports can be an important tool to help you understand differences affecting price. But we must caution you not to let them interfere with what you like or really want. Remember, some diamonds are very beautiful even though they don’t adhere to establish standards. In the final analysis, use your own eyes and ask yourself how you like the stone.

A customer who was trying to decide between several diamonds. Her husband wanted to buy her the stone with the best report, but she preferred another stone which, according to what was on the reports, wasn’t as good. They decide against the best diamond and bought the one that made her happiest. The important thing is that they knew exactly what they were buying, and paid an appropriate price for that specific combination of quality factors. In other words, they made an informed choice. The reports gave them assurance as to the facts, and greater confidence that they knew what they were really comparing.

Improper use of reports can lead to costly mistakes

As important s diamond grading reports can be, they can also be misused and lead to erroneous conclusions and costly mistakes. The key to being able to rely on a diamond report, and having confidence in your decision, lies in knowing how to read it properly. For example, when trying to decide between two diamonds accompanied by diamond grading reports, buyers all too often make a decision by comparing just two factors evaluated on the reports, color and clarity, and think they have made a sound decision. This is rarely the case. No one can make a sound decision based on color and clarity alone. In fact, when significant price differences exists between two stones of the same color and clarity as the more expensive stone, and often it is not the better value. Having the same color and clarity is only part of the total picture. Differences in price indicates differences in quality, differences you may not see or understand. With round diamonds, the information you need is on the report, but you need to understand what all the information means before you can make valid comparisons.

A word of caution: Do not make a purchase relying solely on any report without making sure the report matches the diamond, and that the diamond is still in the same condition described. Always seek a professional gemologist, gemologist-appraiser, or gem-testing laboratory to confirm that the stone accompanying report is, in fact, the stone described there, and that the stone is still in the same condition indicated on the report. There are instances where a report has been accidentally sent with the wrong stone. And, in some cases, deliberate fraud is involved.

How to read a diamond grading report

Check the date issued. It is very important to check the date on the report. It’s always possible that the diamond has been damaged since the report was issued. This sometimes occurs with diamonds sold at auction. Since diamonds can become chipped or cracked with wear, one must always check them. For example, you might see a diamond accompanied by a report describing it as D – Flawless. If this stone were badly chipped after the report was issued, however, the clarity grade could easily drop to VVS, and in some cases, much lower. Needless to say, in such a case value would be dramatically reduced.

Who issued the report? Check the name of the laboratory issuing the report. Is the report from a laboratory that is known and respected? If not, the information on the report may not be reliable. Several well-respected laboratories issue reports on diamonds. The best known in the United States include the Gemological Institute of America Gem Trade Laboratory (GIA/GTL or GIA), and the American Gemological Laboratories (AGL). Respected European labs issuing reports include the Belgian Diamond High Council (HRD). Regardless of which report you are reading, all will provide similar information, including:

Identity of the stone. This verifies that the stone is a diamond. Some diamond reports don’t make a specific statement about identity because they are called diamond reports and are only issued for genuine diamonds. If the report is not called a “diamond grading report” then there must be a statement attesting that it is genuine diamond.

Weight. The exact carat weight must be given.

Dimensions. Any diamond, of any shape, should be measured and the dimensions recorded as a means of identification, especially for insurance/identification purposes. The dimensions given on a diamond report are very prices and provide information that is important for several reasons. First, the dimensions can help you determine that the diamond being examined is, in fact, the same diamond described in the report, since the likelihood of having two diamonds with exactly the same carat weight and millimeter dimensions is remote. Second, if the diamond has been damaged and re-cut since the report was issued, the millimeter dimensions may provide a clue that something has been altered, which might affect the carat weight as well. Any discrepancy between the dimension that you or your jeweler get by measuring the stone, and those provided on the report, should be a red flag to check the stone very carefully.

Finally, the dimensions on the report also tell you whether the stone is round or out of round. Out of round diamonds sell for less than those that are more perfectly round.

Fine diamonds are “well-rounded”.

The diamond’s roundness will affect value, so it is determined very carefully from measurements of the stone’s diameter, gauged at several points around around the circumference. For a round diamond, the report will usually give two diameters, measured in millimeters and noted to the hundredth: for example, 6.51 rather than 6.5; or 6.07 rather than 6.0. These indicate the highest and lowest diameter. Diamonds are very rarely perfectly round, which is why most diamond reports will show two measurements. recognizing the rarity of truly round diamonds, some deviation is permitted, and the stone will not be considered “out of round” unless it deviates by more than the established norm, approximately 0.10 millimeter in a one carat stone. In a one carat diamond, if the difference is 0.10 or less, then the stone is considered “round.” If the difference is greater, it is “out-of-round.”

To calculate an acceptable deviation on a particular stone, average the high and the low diameter dimension given and multiply that number by 0.0154. For example, if the dimensions given are 8.20x 8.31, the diameter average is 8.25 ( (8.20 + 8.31)/2). Multiply 8.25 by 0.0154 = 0.127. This is the acceptable deviation allowable for this stone (between 0.12 and 0.13). The actual deviation in this example would be 0.11 (8.31 – 8.20), well within the tolerance, so this diamond would be considered “round.” Some flexibility is permitted on diamonds over two carats.

Depending on degree of out-of-roundness (how much it deviates from being perfectly round), price can be affected. The greater the deviation, the lower the price should be.

Dimensions for fancy shapes

While dimension for fancy shapes diamonds are not as important as they are for round diamonds, there are length to width ratios that are considered “normal” and deviations may result in price reductions. The following reflect acceptable ranges:

Pear shape: 1.50:1 to 1.75:1

Marquise shape: 1.75:1 to 2.25:1

Emerald shape: 1.50:1 to 1.75:1

Oval shape: 1.50:1 to 1.75:1

To better understand what this means, let’s look at a marquise diamond as an example. If its report showed the length to be 15 millimeters and the width to be 10 millimeters the length to width ratio would be 15 to 10 or 1.5:1. This would be acceptable. If, however, the dimensions were 30 mm long by 10 mm wide, the ratio would be 30 to 10 or 3:1. This would be unacceptable; the ratio is too great, and the result is a stone that looks much too long for its width. Note: A long marquise is not necessarily bad, and some people prefer a longer shape, but it is important to understand that such stones should sell for less than those with normal lengths. Always keep in mind the length to width ratio of fancy cuts, and adjust the price for that are not in the acceptable range.


Leave a Reply