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Measuring Cut Proportions

Some content on this page are contributed by Good Old Gold, with thanks.

Where to get Cut Proportion measurements?

Before we can analyse a diamond's proportions, we need to measure its many facets. Fortunately, GIA and AGS provides quite a few of the necessary measurements required on proportions to make an informed decision, even though there is still room for improvement. For example, they do not provide the measurements of the girdle facet angles required to tell if the diamond has dug or painted girdles.

Fortunately for consumers, we do not have to measure the cut proportion ourselves. If it is not found on the diamond's certificate, get the jeweller who is trying to sell you the diamond to measure it for you. If your jeweller does not have the equipment, or does not believe in measuring the diamond, then it is most likely that the diamond is not of premium quality since he did not analyse it sufficiently before purchasing it for his stock. You need these measurements to buy smart, so ignore them at your own peril.

Similarly, a good gem appraiser should have the means to measure it for you.

There are currently three products on the market that are being used by jewellers and gemologists for measuring a diamond's proportion:

The Gemscope Eyepiece Diamond Proportion Analyzer

Gemscope Eyepiece Diamond Proportion AnalyserThis is an eyepiece that plugs right into a gemological microscope and allows the grader to determine all the proportions of any given stone. This device can measure the table, pavilion, crown, girdle, etc.

Basically it can measure everything except pavilion angles. However, we can deduce the range of pavilion angles from the pavilion depth, so it is not such a big problem.

The grader observes and measures all the various scales using the eyepiece. The diamond will be rotated around and measured at 8 different points and an average is taken on all measurements.

The Standard Full Screen Gem Proportion Analyser

Standard Full Screen Gem Proportion AnalyserAnother tool used to measure the proportions of diamond is the Standard Full Screen Gem Proportion Analyser.

Using this tool the grader observes the silhoutte of the diamond on a translucent screen. The grader observes and measures all the various scales on the screen. The diamond will be rotated around and measured at 8 different points and an average is taken on all measurements.

Using the eyepiece or screen is very tedious and takes some time, but since you are buying the diamond, the jeweller is obligated to measure it for you.

Digital Proportion Analysers (or Diamond Scanners)

The two methods above are considered 'old fashioned'. The accuracy of the measurements for traditional methods of measurement is largely dependent on the skill of the grader. Most people in the diamond trade nowadays use a digital proportion analyser.

The Sarin Digital Proportion Analyser (DiaScan S+) shown here is the simplest and most basic of the digital proportion analysers. It is also the least expensive. The Sarin Company specializes in hardware/software solutions that physically measure a diamond's facets and proportion. However, Sarin is only one of many companies that make proportion analysers. It's main competitors are OctoNus (which makes the Helium diamond scanners) and OGI Systems.

This method of grading and determining the proportions is the fastest and most efficient. Human error is also minimised. The only drawback is that the machine must be calibrated properly. Also, the more expensive machines tend to be more accurate and give better information.

A diamond is placed on a small rotating stand inside this piece of hardware which has a camera built into it. The stone is rotated and measured from every angle by the internal camera. This hardware works in conjunction with software which then gives all the results onscreen. The results can also be printed for the consumers to observe.

These diamond scanners are quite impressive. Look at the sample Helium report below. (You will need Adobe's Acrobat Reader to see the report.) It has information on every single facet of a diamond.

[Click here for a sample of a report created with OctoNus' Helium Polish diamond scanner]



Importance of Cut Proportion Measurement

We have learned that an ideal cut diamond performs well in all the elements of light return. It is high in brightness and contrast. It has dazzling fire in the right lighting, and it has amazing scintillation.

We have also seen, with optical analysis tools, just how these diamonds would look like up close.

Your education would not be complete if you do not know exactly how the facets of a diamond cause the light return effects you observed so far. To do so, you will need to measure these facets. Sometimes, these measures are in angles and sometimes these are in length. Whether we use angles or lengths ly depends on which measure is relevant when we analyse that particular facet.

Cut proportion determines the performance of a diamond. Therefore, the measurements correlate to the optical quality of the diamond. I would advice against buying a diamond unless the jeweller or vendor can present you with this set of information. You are spending thousands of dollars and the least the jeweller or vendor can do is to measure the diamond for you. Do not be short changed.

Next, we shall discuss a diamond's Table Bezels and Pavilion Mains. (Do remember to go back to the page on facet names whenever you need a reminder.)


Next: Table, Bezel and Pavilion Mains...