Understanding Diamonds - Cut and Proportion

The cut of a diamond and the proportioning of the cut - the make - are of extraordinary importance, because they have the greatest influence on the fire (variety and intensity of rainbow colors seen) and brilliance (liveliness or sparkle) of the stone.

We will discuss cut and proportion of the round brilliant cut stone, since this is the most popular cut. It usually displays the stone's qualities to their greatest potential, and is therefore the best "investment" cut.

The following diagram provides an illustration, in its simplest terms, of the effect of cut and proportion on fire and brilliance in a round brilliant-cut stone. Many times we will send a stone to be recut.

To What Extent Do Cut and Proportion Affect Value In Diamonds?

Excellently cut and proportioned stones cost significantly more per carat than those that are not cut well. The following will give a very basic idea of the monetary effect of some of the most frequently encountered defects in cut and proportion.

• Table is not a reasonably accurate octagon: 2% - 15% off
• Girdle is too thick: 5% - 20% off
• Symmetry of crown facets off: 5% - 15% on round, less on fancy cuts since defect is not so easily seen
• Asymmetrical culet: 2% - 5% off
• Misaligned culet: 5% - 25% off
• Stone too shallow: 15% - 20% off
• Stone too thick: 10% - 30% off
• Slightly thin crown: 5% - 20% off
• Slightly thick crown: 5% - 15% off

As you can see, there is a fairly wide range here, depending upon the severity of the error, and only an experienced professional can determine the extent to which the value of a given stone may be lessened. But a quick computation can show that a stone which suffers from several errors (which is fairly common) could certainly have its price per carat significantly reduced.

How a diamond has been cut, polished, and to what proportions and symmetry, are of utmost importance since these factors determine the life, brilliance and dispersion of the diamond. If these cutting factors fall below standard, the appearance of the diamond will be adversely affected. Reflection Refraction Dispersion A) When a ray of light touches the surface of a diamond, part of the light is reflected back, this is external reflection. B) The rest of the ray penetrates the stone and is then reflected toward the center of the diamond. This is known as refraction. C) The ray of light is reflected to the surface, where it is seen as the colors of the spectrum. This is known as dispersion. Execution of the design, the precision of the cutting details and the quality of the polish are collectively called the finish.