Diamond Cut: How Do You Know If Your Diamond is a Good Cut?

wedding diamond ringIn an earlier post located here, the importance of purchasing your diamond that is accompanied by a grading report done by a reputable and highly competent lab such as the GIA (Gemological Institute of America) was stressed and highlighted. This report assures you that the Color and Clarity grades and measurements are accurate.

But this level of information is not enough to tell you if the diamond you’re interested in has been properly proportioned so that it is not too spread and shallow nor narrow and deep in relation to it’s carat weight. A diamond in the first case is referred to as a “fish-eye” and in the second case a “nailhead.”

Above: Two examples of poorly proportioned diamonds that have been “swindled” (diamond-cutter term) for maximum weight retention at the expense of correct proportion. Result: You are paying more for “less”. Note the difference between the ideal proportioned diamond versus the shallow and deep stones.

In both instances the diamond will display significant amounts of light leakage, look glassy, and be visually unattractive.

There are two machines on the market today that do a very good job of measuring a diamond’s proportions and providing you with critical information on a Diamond’s Cut. They are the OGI Scope manufactured by OGI Ltd. and the Sarin machine, manufactured by Sarin Technologies.

Let’s take a look at the OGI machine.

ogi diamond system

The diamond is centered on the pedestal, lid closed, and software activated. The pedestal rotates for approximately 45 seconds allowing the internal camera to map the proportions of the diamond.

The MegaScope accurately and reliably measures the cut of your loose diamonds. Basic measurement accuracy is: 0.02 mm. Keep in mind that there may very well be a slight but statistically insignificant difference between the Megascope measurement of Table and

Depth percentage compared to that of the GIA report. This is because:

1. There is a very slight variability inherent in the Megascope itself,

2. Pedestal Placement varies ever so slightly from one run to the next, and

3. GIA graders take the average of four measurements and round off to the next highest number.

Overall, both the GIA and the Megascope and Sarin proportion analyzers are in agreement.

The properties analyzed in loose diamonds are Weight, Diameter, Crown Angle and Height, Pavilion Angle and Depth, Culet Size, Culet Off Center, Table Size, Table Off Center, Total Depth, and Girdle Thickness.

An additional feature is the Top/Down Report, which shows you the cutting angle and percentage for each of the 8 Crown and 8 Pavilion facets. This information affords you more specificity than just the “averages”, by providing detailed information regarding the cut precision and tolerances of the diamond.

Additionally, the MegaScope is set according to the American Gem Society (AGS) scale for what would qualify as an AGS scale from 0-4 level cut diamond. This Cut Grade is inversely proportional to the level of Cut excellence with 0 being the best.

Above: Detailed Megascope Report. First Report at the top of the page are the averaged numbers for the Table, 8 Crown, 8 Pavillon facets, the girdle facet and the culet facet.

Bottom: Detailed analytical report which displays level of cut precision of each of the upper 8 Crown and lower 8 Pavillon facets.

The less variance in cut angle between facets, the greater is the cut precision of the stone and greater probability that the diamond will refract maximum light to your eye. Note that the above diamond shows incredible Cut precision with variance between upper and lower facet angles of less than one degree ( Facet angles are indicated in Red, facet slope percentages in Blue)

Ask your jeweler to provide you with either a Megascope or Sarin Proportion Analysis of any diamond you are considering for purchase.

Knowledge is the power to make an informed decision and get value for your hard-earned money. You wouldn’t buy a house without a comprehensive and detailed engineer’s report. A diamond should be no different. A reputable jeweler will want to make sure you are fully informed.