Diamonds are forever.
If you walk into a pawnshop or jeweler to invest in a diamond, you’ll want to ensure you’re getting a gemstone worth your money. Apart from using PawnGuru to find a reputable pawnshop or jeweler, knowing what to look for in a diamond cut can save you time and make your search much easier. If you know the terminology and fundamentals of the diamond industry, you can refer to the specific qualities you’re looking for in a diamond’s shine.
Diamond cut is the hands-down most important factor to consider when buying a diamond. The other 3Cs—carat, color, and clarity—are important too, but a diamond’s cut affects radiance more than the other three. Most diamond cutters want to preserve as much carat weight as possible when cutting. This means there is an abundant number of poor cuts on the market which supplement buyers interested in higher carat weight. Even high-quality diamonds with bad cuts will appear dull and lifeless compared to a diamond with an ideal cut.
Read on to understand the fundamentals of diamond cut and how this affects price, light performance, and how it should influence your diamond shopping decisions.
What is a Diamond Cut?
Diamond cut is different from a diamond’s shape. Diamond cut refers to a diamonds interaction with light and how well the diamond performs with light refraction & reflection. An ideal cut will not be too deep or shallow—allowing light to properly refract from the top of the diamond, known as the crown. A diamond which is cut too shallow will leak light from the bottom. A deep cut will disperse light from the side. Since diamonds are set in jewelry this escape of light decreases the diamond’s value. The perfect diamond cut will disperse all light refraction to the crown.
The artistry of cutting and polishing a precious gemstone directly impacts a diamond’s grade along the diamond cut scale. The diamond cut scale was developed by the Gemological Institute of America (GIA). This scale determines a standard for diamond radiance. There are five cut grades ranging from excellent to poor in the scale.
GIA specialists place diamonds in a measuring device which rotates the stone 360-degrees. The device optically captures thousands of measurements to generate a 3-d graphic. With a range of criteria, gemologists factor proportions, culet size, girdle thickness, polish, and symmetry descriptions. Using these parameters, the GIA will give a diamond a cut grade.
Aside from using high-tech instrumentation, gemologists also observe diamonds along three measurable interactions with light: brightness, fire, and scintillation.
A diamond cut will make a diamond’s brightness much more apparent. Brightness is the internal and external white light that reflects from the diamond. The more perfect a diamond’s proportions, the less light leakage and the higher quality of shine. The best environment to observe brightness is outside in the natural light.
Light disperses will appear in a rainbow spectrum as the light reflects from the diamond’s surface. Fire is best observed in dimly lit rooms with warm lighting.
Scintillation is the pattern of dark and light facets that sparkle from refraction from within the diamond. Typical offices and other well-lit rooms’ lighting will give a good demonstration of a diamond’s scintillation.
The GIA Diamond Cut Scale
The top 3% of diamond cuts have the proportions to place a diamond in this diamond cut grading. Virtually all light that enters the diamond will be properly refracted through the crown and into the viewer’s eye.
The top 15% of diamonds will rank into this diamond cut grading. Diamonds ranked as very good will reflect the majority of the light that enters the diamond. An asymmetrical pattern of light and dark spots will be visible, but dullness is also possible.
The top 25% of high-quality diamonds will have a good cut grade. Light reflection occurs but scintillation, fire, and brightness will appear dull with less reflective light interaction.
A fair cut represents the top 35% of diamonds. A cut of this grading will have trouble retaining and refracting light from the stone.
Diamonds with a poor grade are low value and will appear glossy, dull, or glassy to the naked eye.
The proportions of a diamond cut are challenging measurements to evaluate without in-depth knowledge of diamond artistry and the mathematical principles behind light reflection & refraction. Typically, the GIA will use machine instruments to measure a diamond’s proportions.
Without access to this kind of equipment, your best bet is to use tools like the GIA Cut Estimator. Plug in the given proportions of the diamond you’re thinking of buying. The Cut Estimator will give you an analysis of the diamond cut grade. All GIA certified diamonds will have corresponding paperwork outlining proportions.
Table Size: The top horizontal facet of a diamond which should measure between 54-57%.
Depth Percentage: A diamond’s composite depth from the surface of the table to the culet should measure between 57-64%.
Crown Angle: The upper section of a diamond, from the top edge of the girdle, extending to the table. The crown angle should measure between 33.7-35.8 degrees.
Pavilion Angle: The average of the angles formed by the diamond’s pavilion, main facets, and its girdle plane make up the pavilion angle. The ideal pavilion angle measurement is between 40.2-41.24 degrees.
Girdle Thickness: The middle section of a diamond. The girdle is a narrow row which separates the crown from the pavilion. The girdle functions as the diamond’s setting edge. A perfect girdle thickness should be classified between thin and medium.
Culet: A culet is a small point at the bottom which is intended to prevent chipping. The culet size should be none, meaning it’s small enough not to register or inhibit light reflection.