There is a lot of information about what constitutes a perfect diamond, but in reality, such stones are very rare and expensive. It is much more practical to take a look at what makes diamonds less valuable in order to avoid overpaying for low-quality stones.
Below are the most important characteristics that detract from the value of a diamond.
Visible Internal Flaws
One of the things that determine the value of a diamond is the number of internal flaws (inclusions) such as black spots, lines, crystals, etc.
Diamonds are graded for clarity based on how visible these imperfections are when looked at with a loupe or with the naked eye.
The flaws that detract the most from the value of a stone are those that are easily seen from a normal viewing distance and are located prominently, e.g., close to the center of the diamond when viewed from the top.
Also, keep in mind that the closer a flaw such as a crack or line is to the surface of the stone, the more likely the inclusion is to weaken the diamond’s structure.
Chips and Nicks
If a diamond’s surface has been chipped or nicked, the value of the stone will go down depending on how big and numerous the resulting surface flaws are.
For example, if your diamond happens to be chipped, the bigger the chip, the more likely the stone is to break further in the same place if hit again, and this risk diminishes the value of the diamond.
There is no way to repair chipped diamonds without causing the damaged stone to lose value.
One option is to have the diamond recut into a smaller stone so as to eliminate the chip, but since this process involves removing a significant amount of diamond, the resulting stone has a lower carat weight and is worth less.
The most sought-after diamonds are the ones that are completely or nearly colorless. A visible yellowish tint in a stone lowers its color quality grade.
Diamonds with yellow tints sell for less than colorless stones do, and the stronger the yellow coloring, the greater the drop in value is compared with the price of perfectly white stones.
The yellow tint in a diamond with a low color grade can be masked by setting the stone in gold: The tint will blend with the yellow color of the metal and become less visible, making the stone look whiter against the gold backdrop.
The proportions of a diamond’s cut determine how light entering the stone will be reflected back to the eye of the observer.
For example, if a round diamond is cut too shallow or too deep, most of the light will leak out of the stone without being reflected, resulting in low brilliance and sparkle.
The closer a diamond is to the proportions that maximize light reflection and brilliance, the more valuable it will be.
In general, stones whose cut is rated Fair or Poor on the scale introduced by the G.I.A. (Gemological Institute of America) tend to be cheaper than those with an Excellent, Very Good, or Good cut, all else being equal.
However, it is rarely worth it to save money by buying a poorly cut diamond: Not only will it look dull and dark, but its lack of brilliance will also make its other defects (such as internal flaws or yellow tints) more visible.