Diamond has inclusions and its appearance could be affected by factors like cutting. What could affect the scintillation of diamond? The scintillation of both lab grown diamond and natural diamond could be affected by following factors.
1. Refractive index and dispersion
Refractive index and dispersion are fixed physical properties which cannot be controlled artificially whether for natural diamond or lab grown diamond. Diamond has a refractive index of 2.42 and a dispersion rate of 0.044. The higher the refractive index, the higher the ability to reflect light, and thus the more scintillation. Diamond has a high refractive index (2.42) and that is also the highest among all natural gemstones (glass has a refractive index of about 1.5).
Dispersion rate means when white light passes through the facets of a diamond, the light could be divided into spectral colors (red, orange, yellow, green, cyan, indigo, violet), which is what people refer to as “diamond fire”. The scintillation of diamond comes from its refractive index and dispersion.
2. Cutting style
Cutting style is an important artificial factor affecting the scintillation of a diamond. The most common cutting style we see nowadays is brilliant cut. Its cutting proportion is deemed as the one which can present the shininess and brightness of a diamond the most. Under this kind of cutting, the number and size of facets allows the light passing through a diamond to have enough reflection and retain enough brightness. This means the spark of the diamond would not be too faint when viewed with naked eyes. Diamonds of different shape (like round, oval, heart and princess) are also cut with brilliant cut, and are categorized by their outline and referred to as fancy cut.
Step cut is another common cutting style, but it could not create the level of diamond scintillation as brilliant cut does. However, step cut could emphasize the clarity of diamond. Step cut exists because of emerald, so it is also called emerald cut, which is usually used on rectangular gemstones.
3. Cut grade
Cut grade is the artificial factor which affects diamond’s scintillation the most. Cutting decides whether the facets of a gemstone are symmetrical and the facets can accurately reflect all the light. The more the light is reflected inside a diamond, the higher the overall diamond scintillation. The better the cut grade, the more glittering a diamond is.
Common cutting for diamond can be classified into Ideal*, Excellent, Very good, Good, Fair and Poor, with Ideal being the highest grade. Ideal cut originated in 1919 when Mr. Marcel Tolkowsky proposed the formula for diamond ratio based on optical theories. The formula accurately points out the value range of diamond ratio where a diamond would be the brightest when being cut according to this ratio. This is considered the most beautiful diamond cutting worldwide, so the standard for Ideal cut is extremely strict.
*The highest grade of cutting for GIA certificate is Excellent, while the highest grade of cutting for IGI certificate is Ideal, followed by Excellent
4. Clarity
Clarity could affect the scintillation of a diamond to some extent, yet the effect on grade SI or above is negligible. Diamonds of clarity grade I carry obvious flaws, and these flaws could affect the light passing through diamonds, thus affecting the scintillation as a result. Therefore, diamonds of clarity grade I should be avoided unless you have a really tight budget.
